Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at s √ =7 TeV in 2010
aa r X i v : . [ h e p - e x ] A p r EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP-2013-154
Submitted to: EPJC
Muon reconstruction efficiency and momentum resolution ofthe ATLAS experiment in proton–proton collisions at √ s = 7 TeV in 2010
The ATLAS Collaboration
Abstract
This paper presents a study of the performance of the muon reconstruction in the analysis ofproton–proton collisions at √ s = 7 TeV at the LHC, recorded by the ATLAS detector in 2010. Thisperformance is described in terms of reconstruction and isolation efficiencies and momentum res-olutions for different classes of reconstructed muons. The results are obtained from an analysis of
J/ψ meson and Z boson decays to dimuons, reconstructed from a data sample corresponding to anintegrated luminosity of 40 pb − . The measured performance is compared to Monte Carlo predictionsand deviations from the predicted performance are discussed. oname manuscript No. (will be inserted by the editor) Muon reconstruction efficiency and momentum resolutionof the ATLAS experiment in proton–proton collisions at √ s = 7 TeV in 2010 The ATLAS Collaboration Address(es) of author(s) should be giventhe date of receipt and acceptance should be inserted later
Abstract
This paper presents a study of the perfor-mance of the muon reconstruction in the analysis ofproton–proton collisions at √ s = 7 TeV at the LHC,recorded by the ATLAS detector in 2010. This per-formance is described in terms of reconstruction andisolation efficiencies and momentum resolutions for dif-ferent classes of reconstructed muons. The results areobtained from an analysis of J/ψ meson and Z bosondecays to dimuons, reconstructed from a data samplecorresponding to an integrated luminosity of 40 pb − .The measured performance is compared to Monte Carlopredictions and deviations from the predicted perfor-mance are discussed. One of the main components of the ATLAS detectoris its huge Muon Spectrometer (MS). It is based onthe use of three very large air core toroidal magnets,each containing eight superconducting coils, and threemeasuring planes of high-precision chambers. This sys-tem is designed for efficient muon detection even in thepresence of very high particle backgrounds and for ex-cellent muon momentum resolution up to very high mo-menta of ∼ µ m) and the extreme alignment precision of the mea-suring planes (30 µ m). The other very important component of the muonidentification and measurement in ATLAS is the innerdetector (ID) that complements the performance of theMS at momenta below ∼
100 GeV. In ATLAS the veryefficient muon detection and high momentum resolu-tion, with nominal relative momentum resolutions of < .
5% up to transverse momenta p T ∼
200 GeV and <
10% up to p T ∼ J/ψ mesons to access theregion p T <
10 GeV and dimuon decays of Z bosonsto access the region 20 GeV < p T <
100 GeV. The ef-ficiency determination in the region 10 GeV < p T <
20 GeV is not possible due to the limited sample ofmuons with p T higher than 10 GeV in the J/ψ de-cays and difficulties in controlling the backgrounds inthe sample of Z decays that lead to muons with p T smaller than 20 GeV. For these analyses, one of thedecay muons is reconstructed in both detector systemsand the other is reconstructed by just one of the sys-tems in order to probe the efficiency of the other. Thismethod (known as tag-and-probe , and described in moredetail in Sect. 4) is applied to the ATLAS proton–proton ( pp ) collision data recorded at the Large HadronCollider (LHC) in 2010 at a centre-of-mass energy of7 TeV.Muon isolation criteria are used to select muons inmany physics analyses, and measurements of the isola-tion efficiency performed using Z → µ + µ − decays aredescribed in Sect. 9. The invariant mass distributionsfrom these data are also used to extract the muon mo-mentum resolutions. The analysed data sample corre- sponds to the full 2010 pp dataset with an integratedluminosity of 40 pb − [2] after applying beam, detectorand data-quality requirements. A detailed description of the ATLAS detector can befound elsewhere [3]. Muons are independently measuredin the ID and in the MS.The ID measures tracks up to | η | = 2 . exploitingthree types of detectors operated in an axial magneticfield of 2 T: three layers of silicon pixel detectors clos-est to the interaction point, four layers of semiconduc-tor microstrip detectors (SCT) surrounding the pixeldetector, and a transition radiation straw-tube tracker(TRT) covering | η | < . b-layer ) has a radiusof 50 . r ≈ | η | < .
9, far beyond the range over which muons are iden-tified. In the barrel and end-cap, in the region | η | < . λ ) in-cludes 9.7 λ of active calorimeter and 1.3 λ of outer sup-port.The magnetic field of the MS is produced by threelarge air-core superconducting toroidal magnet systems(two end-caps, where the average field integral is about6 Tm, and one barrel, where the field integral is about2.5 Tm). The field is continuously monitored by ap-proximately 1800 Hall sensors distributed throughoutthe spectrometer volume. The deflection of the muontrajectory in this magnetic field is measured via hits inthree layers of precision monitored drift tube (MDT)chambers for | η | < . . ≤| η | < . | η | < .
05) and three layers of ATLAS uses a right-handed coordinate system with its ori-gin at the nominal interaction point (IP) in the centre ofthe detector and the z -axis along the beam pipe. The x -axispoints from the IP to the centre of the LHC ring, and the y -axis points upward. Cylindrical coordinates ( r, φ ) are usedin the transverse plane, φ being the azimuthal angle aroundthe beam pipe. The pseudorapidity is defined in terms of thepolar angle θ as η = − ln tan( θ/ thin gap chambers (TGCs) in the end-caps (1 . < | η | < .
4) are used by the muon trigger (see below).The RPCs, TGCs and CSCs also measure the muontrajectory in the non-bending ( φ ) plane of the spec-trometer magnets. The following text frequently refersto chambers which make a measurement in the bend-ing ( η ) plane as ‘precision chambers’, since these havea much better spatial resolution (important for a goodmomentum resolution) than the chambers used for trig-gering.The chambers are monitored by an optical align-ment system, designed to provide an accuracy of 30 µ min the barrel and 40 µ m in the end-cap [4].The ATLAS detector has a three-level trigger sys-tem: level 1 (L1), level 2 (L2), and the event filter (EF).The MS provides a L1 hardware muon trigger which isbased on hit coincidences in different RPC and TGC de-tector layers within programmed geometrical windowswhich define the muon p T . The L2 and EF muon trig-gers perform a software confirmation of the L1 muontrigger using refined p T measurements from the preci-sion chambers.Figure 1 shows a schematic drawing of the ATLASMS. The barrel muon chambers are installed aroundthe calorimeters in roughly cylindrical rings of approx-imately 5, 7 and 9 m radius. Large barrel chambersare mounted between the barrel toroid coil cryostats.Small barrel chambers are installed on the toroid coilcryostats. The barrel end-cap extra (BEE) chambersare mounted on the end-cap toroid cryostats. The end-cap chambers are arranged in disks with z -axis posi-tions of approximately 7, 13 and 21 m from the centreof the detector, and which are orthogonal to the protonbeams. Muon identification in ATLAS uses independent trackreconstruction in the ID and MS, which are then com-bined. Track reconstruction in the muon spectrometeris logically subdivided into the following stages: pre-processing of raw data to form drift-circles in the MDTsor clusters in the CSCs and the trigger chambers, pattern-finding and segment-making, segment-combining, andfinally track-fitting. Track segments are defined as straightlines in a single MDT or CSC station. The search forsegments is seeded by a reconstructed pattern of drift-circles and/or clusters.Full-fledged track candidates are built from segments,typically starting from the outer and middle stationsand extrapolating back through the magnetic field to
End cap toroid Barrel toroid coil BEE chamber Large barrel chambersSmall barrel chambersFeet End cap chambers
Fig. 1
Schematic drawing of the ATLAS muon spectrometer. the segments reconstructed in the inner stations (thoughother permutations are also explored). Each time a rea-sonable match is found, the segment is added to thetrack candidate. The final track-fitting procedure takesinto account all relevant effects (e.g. multiple scattering,field inhomogeneities, inter-chamber misalignments, etc.).More details about the muon reconstruction can befound in Ref. [1, p.165].A similar approach is followed by the ID track re-construction where the pattern recognition uses space-points formed from the pixel and SCT clusters to gener-ate track seeds. These seeds are then extended into theTRT and drift circles are associated. Finally the tracksare refitted with the information coming from all threedetectors. More details about the ID track reconstruc-tion can be found in Ref. [1, p.19].The analyses presented here make use of three classesof reconstructed muons, as described below.Stand-alone (SA) muon: the muon trajectory is recon-structed only in the MS. The direction of flight andthe impact parameter of the muon at the interac-tion point are determined by extrapolating the spec-trometer track back to the point of closest approachto the beam line, taking into account the energy lossof the muon in the calorimeters.Combined (CB) muon: track reconstruction is performedindependently in the ID and MS, and a combined track is formed from the successful combination ofa SA track with an ID track.Segment-tagged (ST) muon: a track in the ID is iden-tified as a muon if the track, extrapolated to theMS, is associated with at least one segment in theprecision muon chambers.The main goal of this paper is the measurement ofthe reconstruction efficiencies and resolutions for com-bined (CB) and combined-plus-segment-tagged (CB+ST)muons, for which the use of the ID limits the acceptanceto | η | < .
5. Stand-alone muons are employed to mea-sure the muon reconstruction efficiency in the ID.The CB muon candidates constitute the sample withthe highest purity. The efficiency for their reconstruc-tion is strongly affected by acceptance losses in the MS,mainly in the two following regions: – at η ∼
0, the MS is only partially equipped withmuon chambers in order to provide space for servicesof the ID and the calorimeters; – in the region (1 . < | η | < .
3) between the bar-rel and the end-caps, there are regions in φ whereonly one layer of chambers is traversed by muons inthe MS, due to the fact that some chambers werenot yet installed in that region during the 2010-2012data-taking. Here no stand-alone momentum mea-surement is available and the CB muon reconstruc-tion efficiency is decreased. The reconstruction algorithms for ST muons havehigher efficiency than those for CB muons as they canrecover muons which did not cross enough precisionchambers to allow an independent momentum measure-ment in the MS. They are also needed for the recon-struction of low- p T muons which only reach the inner-most layer of the muon chambers. Due to their lowerpurity and poorer momentum resolution, ST muons areonly used in cases where no CB muon can be recon-structed.In the early phase of the LHC operation, ATLASused two entirely independent strategies for the recon-struction of both the CB and ST muons. These twoapproaches, known as chain 1 and chain 2 in the fol-lowing, provide an invaluable cross-check on the per-formance of a very complex system, and allow ATLASto ultimately take the best aspects of both. The chainshave slightly different operating points, with chain 1typically more robust against background, whilst chain 2has a slightly higher efficiency.In chain 1, the momentum of the muon is obtainedfrom a statistical combination of the parameters of thetracks reconstructed by the ID and MS [1, p.166]. SAmuon tracks are required to have a sufficient number ofhits in the precision and trigger chambers, to ensure areliable momentum measurement. In chain 2, the com-bined muon momentum is the result of a simultaneoustrack fit to the hits in the ID and the MS. The require-ments applied to the hit multiplicities in the MS areless stringent than in chain 1 because certain informa-tion, such as the trajectory in the plane transverse tothe proton beams, is better provided by the ID in thesimultaneous fit. In both chains, muon track segmentscan additionally be assigned to ID tracks to form STmuons, based on the compatibility of the segment withthe extrapolated ID track.To illustrate the high purity of the ATLAS muonidentification and the size of the dimuon dataset, Fig. 2shows the reconstructed invariant mass distribution ofopposite-sign muon candidate pairs. The events are se-lected by an unprescaled, 15 GeV p T threshold singlemuon trigger, which is reconfirmed offline by requiringat least one muon to have p T >
15 GeV. Both muonsare required to be of CB type and to pass the ID trackselection criteria of Sect. 6.2. The distance of closestapproach of the muon to the primary vertex is limitedto 5 mm in the transverse plane and 200 mm/sin θ inthe longitudinal direction. The J/ψ , Υ and Z peaks areclearly visible, and the muon reconstruction has the ca-pability to resolve close-by resonances, such as the J/ψ and ψ ′ as well as the Υ (1 S ) and Υ (2 S ). The shouldernear m µµ ≈
15 GeV is caused by the kinematic selec-tion. [GeV] µµ m1 10 ] - [ G e V µµ / d m µµ d N -1
10 [GeV] µµ m1 10 ] - [ G e V µµ / d m µµ d N -1 ATLAS = 7 TeVsData 2010, -1
40 pb ≈ L ∫ ρ / ω φ ψ J/ ’ ψ (1S) Υ (2S) Υ Z Fig. 2
Reconstructed invariant mass, m µµ , distribution ofmuon candidate pairs. The number of events is normalisedby the bin width. The uncertainties are statistical only. As track reconstruction is performed independently inthe ID and MS, the reconstruction efficiency for CB orST muons is the product of the muon reconstructionefficiency in the ID, the reconstruction efficiency in theMS, and the matching efficiency between the ID andMS measurements (which includes the refit efficiencyin the case of chain 2). It is therefore possible to studythe full reconstruction efficiency by measuring these in-dividual contributions. A tag-and-probe method is em-ployed, which is sensitive to either the ID efficiency orthe combined MS and matching efficiency. This tech-nique is applied to samples of dimuons from the
J/ψ and Z decays.For Z → µ + µ − decays, events are selected by re-quiring two oppositely charged isolated tracks with adimuon invariant mass near the mass of the Z boson.One of the tracks is required to be a CB muon can-didate, and to have triggered the readout of the event(see Sect. 6). This muon is called the tag . The othertrack, the so-called probe , is required to be a SA muonif the ID efficiency is to be measured. If the MS recon-struction and matching efficiency is to be measured theprobe must be an ID track. The ID reconstruction effi-ciency is defined as the fraction of SA probes which canbe ascribed to an inner detector track. The combinedMS and matching efficiency is the fraction of ID probeswhich can be associated to a CB or ST muon. Efficiencies determined with the tag-and-probe method, andwith an alternative method based on Monte Carlo generator-level information, were found to agree to within statisticaluncertainties [1, p.221], which also shows that any possiblecorrelations between the tag and probe muons are negligible. m [GeV]70 80 90 100 110 120 C oun t s / G e V Before tag isolation cutAfter tag isolation cutAfter tag isolation cutData 2010=7 TeVs -1 L dt=40 pb ! After tag and probe isolation cut
ATLAS
Fig. 3
Invariant mass, m , distribution of pairs of tag muons(chain 2) and ID track probes for different sets of muon iso-lation requirements for the Z boson analysis, as indicated inthe legend. m [GeV]2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 C oun t s / . G e V -1 Ldt = 40 pb ∫ = 7 TeV sp > 3 GeV 4 GeV ≤ T ≤ | η UnmatchedID probesMatchedID probes
CB Gauss+quadratic fitCB+ST Gauss+quadratic fitCB Gauss+quadratic fitCB+ST Gauss+quadratic fit
ATLAS
Fig. 4
Distribution of the invariant mass, m , of the un-matched (upper distributions) and matched (lower distribu-tions) tag-and-probe pairs for CB and CB+ST muons of chain2, for the J/ψ analysis with a probe muon selection as de-scribed in the legend. Also shown are the results of the fitusing a Gaussian signal and a quadratic background contri-bution.
The invariant mass spectra of Z boson tag-and-probe pairs, shown in Fig. 3, illustrate how muon isola-tion requirements (see Sects. 6 and 9) almost entirely re-move contributions from background processes, result-ing in a relatively pure sample of muon tag-and-probepairs. Monte Carlo studies show that the contributionfrom other sources is below 0.1% when MS probes areused and below 0.7% when ID probes are used. Thesebackgrounds arise from Z → τ + τ − , W ± → µ ± ( ¯ ν ) µ W ± → τ ± ( ¯ ν ) τ b ¯ b , c ¯ c , and t ¯ t . The presence of back-grounds in the data leads to an apparent decrease inthe muon efficiency in the range p T .
30 GeV, forboth reconstruction chains. This is taken into accountby comparing the measured efficiencies to efficienciespredicted using simulated samples which include thesebackground contributions.To investigate the reconstruction efficiency at lowertransverse momenta, dimuon pairs from
J/ψ → µ + µ − decays are used in the same way as those from Z → µ + µ − decays. Because J/ψ mesons are produced in-side jets, isolation requirements cannot be used to se-lect a pure sample. In this case, the invariant massdistribution of the tag-and-probe pairs is fitted usingthe sum of a quadratic background term and a Gaus-sian signal term [5]. This is illustrated in Fig. 4 forprobe muons selected in the range 0 . < | η | < . < p T < The measurements presented in this paper are com-pared with predictions of Monte Carlo (MC) simula-tions. For the efficiency measurements in the region p T >
20 GeV, five million Z → µ + µ − events weresimulated with PYTHIA 6.4 [6], passed through thefull simulation of the ATLAS detector [7], based onGEANT4 [8,9], and reconstructed with the same re-construction programs as the experimental data.During the 2010 data taking, the average number of pp interactions per bunch crossing was about 1.5. This“pile-up” is modelled by overlaying simulated minimumbias events on the original hard-scattering event. It isfound to have a negligible impact for these measure-ments. The following background samples were used: Z → τ + τ − , W ± → µ ± ( ¯ ν ) µ W ± → τ ± ( ¯ ν ) τ b ¯ b , c ¯ c , and t ¯ t .More details can be found in Ref. [10]. η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 [ G e V ] T p CB ATLAS
Simulation η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 [ G e V ] T p CB+ST
ATLAS
Simulation
Fig. 5
The chain 1 muon reconstruction efficiency from sim-ulated
J/ψ decays for CB (top) and CB+ST (bottom) muonsas a function of η and p T for efficiency values above 50%. The reconstruction efficiency at low p T was stud-ied with a simulated sample of five million prompt J/ψ events generated with PYTHIA using the PYTHIA im-plementation of the colour-octet model. In order to in-crease the number of events at the higher end of thelow- p T region, this sample was supplemented with asample of one million pp → b ¯ b events also generatedwith PYTHIA, in which at least one J/ψ decaying intomuons of p T > . b -quarkdecay chain.The reconstruction efficiencies obtained from theanalysis of the J/ψ
Monte Carlo samples are shown inFig. 5, as a function of p T and η , for CB and CB+STmuons from chain 1. The most discernible features arethe areas of lower efficiency at fixed η that result fromthe un-instrumented (‘crack’) region in the MS at η ∼ . < | η | < .
3) and themagnetic field (1 . < | η | < .
7) are rather non-uniform.Also visible is the impact of the energy loss in thecalorimeter on the efficiency, for muons with p T of lessthan 2–5 GeV (depending on the η region), which areabsorbed in the calorimeter. For | η | < .
0, the CB+STmuon reconstruction starts to be efficient at p T valueslower than in the reconstruction of pure CB muons,since it includes muons reaching only the inner layer ofMDT chambers. For | η | > . p T dependence of the reconstruction efficiency atlow p T .For the J/ψ → µ + µ − analysis the measured effi-ciencies are separated into five pseudorapidity intervalsaccording to the different MS regions: | η | < . η = 0 crack region;0 . < | η | < . . < | η | < . . < | η | < . . < | η | < . Z → µ + µ − decays were required to have p T >
20 GeV. In contrast to the case of lower- p T muonsfrom J/ψ decays, the φ deflections of these muons bythe magnetic fields in the detector are so small that onecan use the muon directions of flight at the pp interac-tion point to associate them with specific ( η, φ ) regionsof the MS. Ten different regions are defined, correspond-ing to ten different physical regions in the MS [3]. Ineach of these, the muon traverses a particular set ofdetector layers and encounters a different quality of de-tector alignment, a different amount of material or adifferent magnetic field configuration. The ten regionsare described below (see also Fig. 1). – Barrel large : the regions containing large barrel cham-bers only, which are mounted between the barreltoroid coils. – Barrel small : the regions containing small barrelchambers only, which are mounted on the barreltoroid coils. – Barrel overlap : the regions where small and largebarrel chambers have slight overlaps in acceptance. – Feet : the detector is supported by ‘feet’ on its bot-tom half, which results in a loss of acceptance due to missing chambers, making muon reconstructionmore challenging. – Transition : the region 1 . < | η | < .
3, between thebarrel and the end-cap wheels. – End-cap small : the small end-cap sectors, consistingof MDT chambers. – End-cap large : the large end-cap sectors, consistingof MDT chambers and which (in contrast to the
Barrel large regions) contain the toroid coils. – BEE : the regions containing barrel end-cap extrachambers, which are mounted on the end-cap toroidcryostats. – CSC small : the end-cap sectors consisting of smallCSC chambers. – CSC large : the end-cap sectors consisting of largeCSC chambers.
J/ψ → µ + µ − decays, a combined muon isrequired, with minimum p T thresholds of 4, 6, 10, or13 GeV (as it was necessary to increase the thresholdsduring the year, in order to keep the trigger rate withinlimits). For the studies with Z → µ + µ − decays, eventshave to pass the lowest p T threshold muon trigger thatwas unprescaled. The thresholds of the selected triggersrange from 10 GeV to 13 GeV, well below the transversemomentum threshold of the tag muon in the analysis.To suppress non-collision background events, a recon-structed collision vertex with at least three associatedID tracks is required.6.2 Inner detector track selectionTracks in the ID are required to satisfy requirements onthe number of hits in the silicon detectors for qualify-ing as a muon candidate. They must have at least twopixel hits, including at least one in the b-layer, and atleast six SCT hits. In order to reduce inefficiencies dueto known inoperative sensors, the latter are countedas hits for tracks crossing them. Within | η | < .
9, agood-quality extension of the muon trajectory into theTRT is enforced by requirements on the numbers of as-sociated good TRT hits and TRT outliers. The TRToutliers appear in two forms in the track reconstruc-tion: as straw tubes with a signal from tracks other than The fraction of inoperative sensors was ≈
3% for the pixeldetector and <
1% for the SCT. the one in consideration, or as a set of TRT measure-ments in the extrapolation of a track which fail to forma smooth trajectory together with the pixel and SCTmeasurements. The latter case is typical of a hadrondecay-in-flight, and can be rejected by requiring thatthe outlier fraction (the ratio of outliers to total TRThits) is less than 90%. In the region | η | < . | η | the requirement on the total num-ber of TRT hits and outliers is not applied, but trackswhich do pass it are also required to pass the cut on theoutlier fraction. These quality cuts suppress fake tracksand discriminate against muons from π/K decays.6.3 Tag selectionFor each of the two reconstruction chains, tag muons aredefined as CB muons from the interaction vertex. Dif-ferent selection cuts are applied for the measurementsusing J/ψ → µ + µ − and Z → µ + µ − decays to accountfor the different kinematics and final-state topologies.For the studies with J/ψ → µ + µ − a tag muon has topass the following requirements: – the tag muon triggered the readout of the event; – p T > | η | < . – the distance of closest approach of the muon to theprimary vertex, in the transverse plane, has trans-verse coordinate | d | < . | z | < . | d | /σ ( d ) < | z | /σ ( z ) <
3, respectively.For the studies with Z → µ + µ − decays an additionalquantity is used, namely track isolation T ∆R< . = P p T ( ∆R < . / p T (tag) , (1)where the sum extends over all tracks with p T > ∆R ≡ p ( ∆η ) + ( ∆φ ) = 0 . – the tag muon triggered the readout of the event (re-stricting the tag muon to the trigger acceptance, | η | < . – p T >
20 GeV; – T ∆R< . < . They have to satisfy the following criteria for studiesusing
J/ψ → µ + µ − decays: – an ID track fulfilling the hit requirements describedin Sect. 6.2 (SA muons are not used, as the ID effi-ciency is not measured using these decays); – reconstructed momentum, p > | η | < . – the tag and the probe are oppositely charged; – the tag and the probe must be associated with thesame vertex; – ∆R < . – the invariant mass of the tag-and-probe pair is withinthe range of 2 < m < . Z → µ + µ − decays: – an ID track fulfilling the hit requirements or a SAmuon with at least one φ measurement; – p T >
20 GeV, | η | < . – the tag and the probe are oppositely charged; – the tag and the probe are associated with the samevertex; – azimuthal separation of the tag and the probe, ∆φ > . – T ∆R< . < . – the invariant mass of the tag-and-probe pair is within10 GeV of m Z .6.5 Matching of probes to ID tracks and muonsAfter selecting all tag-and-probe pairs, an attempt ismade to match probe tracks to the objects for whichthe efficiency is to be measured, i.e. SA probe tracks toID tracks in the case of the ID efficiency, or ID tracksto CB or CB+ST muons in the case where the recon-struction efficiencies for these two classes of muons areinvestigated. A match between an ID probe and a recon-structed muon is considered successful if they have thesame charge and are close in ( η, φ ) space: ∆R ≤ . ∆R ≤ . p T reconstruction efficiency measuredwith J/ψ → µ + µ − decays Figures 6 and 7 show the reconstruction efficiencies forchain 1 and chain 2 with respect to ID tracks with mo-mentum p > p T ,for the five bins in probe | η | described in Sect. 5. Alsoshown are the Monte Carlo predictions, which agreewith data within the statistical and systematic uncer-tainties of the measurements. A number of checks were performed to study thedependence of the results on analysis details and as-sumptions.1. Signal shapes: the means and the widths of the two(matched and unmatched) Gaussians in the fit wereallowed to vary independently.2. Background shape: a linear background function wasused in the fit, instead of the quadratic parameter-isation; in this case the fit was performed in thereduced mass range of 2.7–3.5 GeV (instead of 2.0–3.6 GeV).3. Alternative fit: an independent fit to the matchedand the total (matched + unmatched) distributions,rather than to matched and unmatched, was usedand the efficiency estimated as the ratio of the sig-nal normalisations in the two distributions. Whilethis option does not provide for an easy propagationof the uncertainty from the background subtractionand does not directly account for the correlationsbetween the two samples, it profits from a higherstability of the two simpler fits, whereas the defaultmethod needs some care in the choice of the initialconditions, in particular in cases of very high effi-ciency or small overall sample size.The largest positive and negative variations obtainedfrom any of the three checks were taken as systematicuncertainties and added in quadrature to the statisticaluncertainty to obtain the total upper and lower uncer-tainties. The statistical uncertainties were found to beat the level of a few percent. [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 0.1 η | ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 1.1 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 1.3 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 2.0 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 2.5 η ATLAS p > 3 GeV= 7 TeVs −1 Ldt = 40 pb ∫ CB+ST MC Chain 1CB+ST Chain 1CB MC Chain 1CB Chain 1
Fig. 6
Efficiency for chain 1 CB and CB+ST muons with momentum p >
J/ψ decays), as a function of p T , forfive bins in | η | as described in the legend, for data and MC events. The error bars represent the statistical uncertainties whilethe bands around the data points represent the statistical and systematic uncertainties added in quadrature.0 [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 0.1 η | ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 1.1 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 1.3 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 2.0 η ATLAS [GeV] T p0 2 4 6 8 10 E ff i c i en cy | < 2.5 η ATLAS p > 3 GeV= 7 TeVs −1 Ldt = 40 pb ∫ CB+ST MC Chain 2CB+ST Chain 2CB MC Chain 2CB Chain 2
Fig. 7
Efficiency for chain 2 CB and CB+ST muons with momentum p >
J/ψ decays), as a function of p T , forfive bins in | η | as described in the legend, for data and MC events. The error bars represent the statistical uncertainties whilethe band around the data points represents the statistical and systematic uncertainties added in quadrature.1 p T reconstructionefficiencies measured with Z → µ + µ − decays For higher momentum muons, with p T >
20 GeV, Z de-cays are used to measure the reconstruction efficiencies.8.1 Inner detector reconstruction and identificationefficiencyFigure 8 shows the reconstruction and identification ef-ficiency in the ID as a function of η , for data and sim-ulation, as determined using SA probes. The simula-tion includes all considered backgrounds. The scale fac-tors (SF), defined as the ratio of the data efficiency tothe Monte Carlo efficiency, are displayed in the lowerpanel (the smallness of the background correction, asdescribed in Sect. 4, means that its effect on the SF isnegligible).As discussed earlier, the efficiency for the combinedreconstruction varies with the detector region, and with p T in the range below 6 GeV. In contrast, the ID re-construction efficiency is independent of φ and p T [3],and shows only a slight dependence on η .The slightly lower efficiencies at η ∼ | η | ∼ η ∼
0, ID trackspass through an inactive region near the middle of theTRT barrel where straws produce no TRT hits; at | η | ∼
1, there is a small region in the transition betweenthe barrel and the end-caps of the ID in which muonscross fewer than six SCT sensors [3]. The measuredID muon reconstruction and identification efficienciesagree with the Monte Carlo predictions within 1%, and,for the most part, within the statistical uncertainties.The average ID efficiency is 0.991 ± p T and η , for data andsimulation (with all considered backgrounds included).The scale factors are displayed in the lower panel ofeach plot.The mean value of the η -dependent scale factor is0 . ± .
003 for chain 1 and 0 . ± .
002 for chain 2,where the errors are statistical. The 1% deviation fromunity in the overall efficiency scale factor of chain 1is caused mainly by the data/MC disagreement in the E ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 S F Fig. 8
Measured ID reconstruction and identification effi-ciency for muons (from Z decays), as a function of η , fordata and Monte Carlo simulation. The scale factors (SF),defined as the ratio of the measured efficiency to the pre-dicted efficiency, are shown in the lower panel of the plot.The uncertainties are statistical. The systematic uncertaintyis discussed in Sect. 8.4. transition region (SF = 0 . p T agree, within 1.5standard deviations, with the average scale factor forthe algorithm in question.The background-corrected efficiencies for CB muonsare shown in Fig. 10. The background is estimated fromMonte Carlo simulation, as described in Sect. 4, and issubtracted bin by bin. The average CB muon recon-struction efficiency is 0 . ± .
002 for chain 1 and0 . ± .
001 for chain 2. The difference in efficiencybetween the two chains arises mainly from the morestringent requirements on the reconstructed MS tracksin chain 1. The ratios between data and MC efficienciesare almost identical to the SFs already discussed forFig. 9 as a consequence of the smallness of the back-ground correction.8.3 Reconstruction efficiencies for CB+ST muonsThe degree to which segment tagging can recover somemuons, in particular in detector regions with only par- E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS
Simulation Data 2010 = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS
Simulation = 7 TeV s
Data 2010 B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Simulation Data 2010 [GeV] T p20 30 40 50 60 70 80 90 100 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Simulation Data 2010 [GeV] T p20 30 40 50 60 70 80 90 100 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Simulation Data 2010 η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Simulation Data 2010 η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 S F Fig. 9
Reconstruction efficiencies (relative to the ID efficiency) and scale factors for CB muons (from Z decays) as a functionof detector region, muon p T and muon η as indicated in the figure. The efficiencies for the two reconstruction chains, obtainedfrom data (without background correction) and Monte Carlo simulation (including backgrounds) are shown in the upperpart of each figure. The corresponding scale factors are shown in the lower panels. The uncertainties are statistical only. Thesystematic uncertainties are discussed in Sect. 8.4. tial muon coverage, is studied by measuring the ef-ficiency for CB+ST muons. The same tag-and-probemethod is used with the only difference being that theprobe is matched to a CB or ST muon. Figure 11 showsthe measured CB+ST muon efficiencies as functions ofthe detector region, p T and η , in comparison with the corresponding CB muon efficiencies. The gains in ef-ficiency when using ST muons in addition to the CBmuons are presented in the lower panels of the plots.These are largest in the ATLAS Feet (13%) and Tran-sition (15%) regions of the detector for chain 1. Forchain 2 the largest gain is 3% in the Feet and BEE B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll E ff i c i en cy Chain 1 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll E ff i c i en cy Chain 2 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s [GeV] T p20 30 40 50 60 70 80 90 100 E ff i c i en cy Chain 1 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s [GeV] T p20 30 40 50 60 70 80 90 100 E ff i c i en cy Chain 2 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 E ff i c i en cy Chain 1 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 E ff i c i en cy Chain 2 −1 Ldt = 40 pb ∫ ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s
Fig. 10
Background-corrected efficiencies for CB muons (from Z decays) as a function of detector region, muon p T and muon η as indicated in the figure, obtained from data and Monte Carlo simulation for the two reconstruction chains. The uncertaintiesare statistical only. The systematic uncertainties are discussed in Sect. 8.4. regions. Figure 11 also shows that the two chains havesimilar overall efficiencies for CB+ST muons, 0.970 ± ± ± ± m Z and the cut on E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS
Data 2010 CB+ST Data 2010 CB = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll R a t i o E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS
Data 2010 CB+ST Data 2010 CB = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll R a t i o E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Data 2010 CB+ST Data 2010 CB [GeV] T p20 30 40 50 60 70 80 90 100 R a t i o E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Data 2010 CB+ST Data 2010 CB [GeV] T p20 30 40 50 60 70 80 90 100 R a t i o E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Data 2010 CB+ST Data 2010 CB η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 R a t i o E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Data 2010 CB+ST Data 2010 CB η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 R a t i o Fig. 11
Efficiencies for CB+ST muons (from Z decays) in comparison to those for CB muons only, for the two reconstructionchains and as a function of detector region, muon p T and muon η as indicated in the figure. The relative gain is shown in thelower panel of each figure. The uncertainties are statistical only. The systematic uncertainties are discussed in Sect. 8.4. the transverse momentum of the tag are each variedwithin ± σ of the m µ + µ − and p T resolutions. Othercuts are varied by ± ±
10% and the re-sulting differences in the scale factors are consideredas additional systematic uncertainties. The individualuncertainties are considered to be uncorrelated and are added in quadrature to estimate the total systematicuncertainty. For values which result from an upwardsand downwards variation, the larger value is used. Thelargest contribution arises from the level of backgroundcontamination, which depends primarily on the choiceof the mass window and the normalisation of the back-grounds. Another important contribution is due to thevariation of the probe isolation criteria. The overall sys- E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS
Simulation (Ζ→µµ)
Data 2010, bkg corrected = 7 TeV s B a rr e l l a r ge B a rr e l s m a ll B a rr e l o v e r l ap F ee t T r an s i t i on E nd − c ap l a r ge E nd − c ap s m a ll BEE F o r w a r d l a r ge F o r w a r d s m a ll S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Simulation (Ζ→µµ)
Data 2010, bkg corrected [GeV] T p20 30 40 50 60 70 80 90 100 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Simulation (Ζ→µµ)
Data 2010, bkg corrected [GeV] T p20 30 40 50 60 70 80 90 100 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 1
ATLAS = 7 TeV s
Simulation (Ζ→µµ)
Data 2010, bkg corrected η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 S F E ff i c i en cy −1 Ldt = 40 pb ∫ Chain 2
ATLAS = 7 TeV s
Simulation (Ζ→µµ)
Data 2010, bkg corrected η −2.5 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 2.5 S F Fig. 12
Efficiencies for CB+ST muons (from Z decays), for the two reconstruction chains as a function of detector region,muon p T and muon η as indicated in the figure. The efficiencies are obtained from data with background correction andfrom Monte Carlo simulation of the signal. The corresponding scale factors are shown in the lower panel of each plot. Theuncertainties are statistical only. The systematic uncertainty is discussed in Sect. 8.4. tematic uncertainty on the CB muon efficiency is 0 . Muon isolation is a powerful tool for a high-purity eventselection in many physics analyses, and is also used forrejecting muons from hadron decays in the Z decaytag-and-probe analyses presented here. It is thereforedesirable to quantify the reliability of the Monte Carloprediction of the isolation efficiency (simulated using ∑ p T ( ∆ R < 0.4) / p T ( µ )0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 E n t r i e s −1 ATLAS −1 Ldt = 40 pb ∫ = 7 TeV s Data 2010 → µµ
Z bb cc → µν W → ττ Z tt ∑ E T ( ∆ R < 0.4) / p T ( µ )0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 E n t r i e s −1 ATLAS −1 Ldt = 40 pb ∫ = 7 TeV s Data 2010 → µµ
Z bb cc → µν W → ττ Z tt ∑ p T ( ∆ R < 0.3) / p T ( µ )0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 E n t r i e s −1 ATLAS −1 Ldt = 40 pb ∫ = 7 TeV s Data 2010 → µµ
Z bb cc → µν W → ττ Z tt ∑ E T ( ∆ R < 0.3) / p T ( µ )0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 E n t r i e s −1 ATLAS −1 Ldt = 40 pb ∫ = 7 TeV s Data 2010 → µµ
Z bb cc → µν W → ττ Z tt
Fig. 13
Comparison of the measured track isolation (left) and calorimeter isolation (right) distributions of the probe muon(from Z decays) with the Monte Carlo predictions, for two different cone sizes using the isolation variables defined in the text.The upper and lower plots correspond to ∆R = 0 . ∆R = 0 .
3, respectively. The simulation includes the effects of pile-up,as described in the text. The uncertainties are statistical.
PYTHIA). This is studied using the same event se-lection that was used for the reconstruction efficiencymeasurements, up to and including the selection of thetag muon (the specific chain used is not shown, since theperformance is comparable for both). In this case, theprobe muon is defined as a CB muon with p T >
20 GeVthat fulfils the ID hit requirements described in Sect. 6.We consider the following isolation variables: – track isolation – the summed p T of tracks (exclud-ing that of the muon) in cones of size ∆R = 0 . ∆R = 0 . p T ofthe muon; – calorimeter isolation – the transverse energy ( E T )deposition in the calorimeter in cones of size ∆R =0 . ∆R = 0 . p T of the muon. The effects of pile-up are taken into account in the simula-tion as described in Sect. 5. The track isolation, T ∆R< . , was defined in Sect. 6.3. The tag-and-probe selections, as described in Sect. 6,only make use of T ∆R< . < .
2. However, the choice ofisolation criteria depends on the analysis and this sec-tion presents the comparisons of data and Monte Carlosimulations for the following combinations of isolationvariables: – T ∆R< . < . E ∆R< . /p T ( µ ) < . – T ∆R< . < . E ∆R< . /p T ( µ ) < . – T ∆R< . < . E ∆R< . /p T ( µ ) < . p T , of the isolation efficiency,which is defined as the fraction of probe muons passinga given set of isolation cuts.The measured isolation efficiencies and the corre-sponding Monte Carlo predictions are compared forchain 1 in Fig. 14; the results for chain 2 are consis-tent. Experimental and simulated data agree within un- M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 T ∆ R < 0.4isol < 0.2 [GeV] T p20 30 40 50 60 70 80 90 100 S F M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 E ∆ R < 0.4T / p T (µ) < 0.2 [GeV] T p20 30 40 50 60 70 80 90 100 S F M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 T ∆ R < 0.4isol < 0.1 [GeV] T p20 30 40 50 60 70 80 90 100 S F M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 E ∆ R < 0.4T / p T (µ) < 0.1 [GeV] T p20 30 40 50 60 70 80 90 100 S F M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 T ∆ R < 0.3isol < 0.1 [GeV] T p20 30 40 50 60 70 80 90 100 S F M uon i s o l a t i on e ff i c i en cy −1 Ldt = 40 pb ∫ ATLAS = 7 TeV s
Simulation Data 2010 E ∆ R < 0.3T / p T (µ) < 0.1 [GeV] T p20 30 40 50 60 70 80 90 100 S F Fig. 14
Isolation efficiencies for muons from Z decays as a function of p T , for track isolation (left) and calorimeter isolation(right) requirements with different isolation cone radii, ∆R , as described in the legend. The Monte Carlo predictions includebackground processes as well as the Z signal. The uncertainties are statistical only. certainties. The lower efficiencies at low p T are mainlycaused by the fact that the p T and E T sums, which de-pend only weakly on the muon p T , are divided by thisquantity, leading to isolation variables that rise withdecreasing muon p T . They are also partially due to thebackground, which is non-negligible in the low- p T re-gion.
10 Measurement of the muon momentumresolution
The muon momentum resolution of the ATLAS detec-tor depends on the η , φ , and p T of the muon [3]. Inthe ID, the p T dependence of the relative momentumresolution can be parameterised to a good approxima- tion [1] by the quadratic sum of two terms, σ ID ( p T ) p T = a ID ( η ) ⊕ b ID ( η ) · p T for 0 < | η | < . σ ID ( p T ) p T = a ID ( η ) ⊕ b ID ( η ) · p T tan ( θ ) for 2 . < | η | < . . The first term describes the multiple scattering contri-bution, whilst the second term describes the intrinsicresolution caused by the imperfect knowledge of themagnetic field in the ID, by the spatial resolution ofthe detector components, and by any residual misalign-ment of the detector components. For | η | > .
0, thebest parameterisation of the second term is given by b ID ( η ) · p T / tan ( θ ). Measurements (from data) of thematerial distribution in the ID [11,12] constrain a ID ( η )to values which agree with the Monte Carlo predictionto within 5% in the barrel and 10% in the end-caps. Theparameter b ID ( η ) is derived from the dimuon invariantmass resolution in Z → µ + µ − decays.The stand-alone muon resolution can be parame-terised as follows: σ SA ( p T ) p T = a MS ( η, φ ) ⊕ b MS ( η, φ ) · p T ⊕ c ( η, φ ) p T , (3)where the first two terms parameterise the effect of themultiple scattering and the contribution of the intrin-sic momentum resolution of the MS, respectively. Thethird term parameterises the effect of the fluctuationsof the muon energy loss in the calorimeters, but thisis small for the momentum range under considerationand is fixed to the value predicted by MC simulation.A special data set, recorded in 2011, with no toroidalmagnetic field in the MS, was used to simulate high-momentum (i.e. straight) tracks and estimate b MS ( η, φ ),yielding b MS ( η, φ ) ∼ . − in the barrel and theMDT end-cap region (excluding the transition region)and ∼ . − in the CSC end-cap region, with arelative accuracy of about 10% in both regions. Thisspecial data set made it possible to improve the align-ment of the muon chambers, leading to b MS ( η, φ ) . . − everywhere in the MS in 2011.Figure 15 shows the dimuon invariant mass resolu-tion of the ID in Z → µ + µ − decays as a function of thepseudorapidity interval of the decay muons, where bothare required to lie in the same interval. The mass reso-lution is the width of a Gaussian which, when convolvedwith the generator-level dimuon invariant mass, repro-duces the dimuon invariant mass distribution observedin data. The ID dimuon invariant mass resolution isbest in the barrel, where it is about 2 GeV, is betterthan 3 GeV for | η | < . . < | η | < .
5. The degradation of the mass res-olution with increasing | η | is primarily caused by thefact that as | η | increases there is a lower field integralper track. That the dimuon invariant mass resolutionmeasured in experimental data is worse than predicted(typically by about 30%), is attributed to residual in-ternal misalignments of the ID. The internal alignmentof the ID was performed by minimising track residuals.This procedure has certain ambiguities which can beresolved by adding constraints such as the requirementthat the energy/momentum ratio ( E/p ) distributions ofelectrons and positrons be the same. These constraintswere only introduced into the alignment procedure forthe 2011 data [13], in which a significantly improveddimuon invariant mass resolution is observed.Due to the toroidal magnetic field, the relative mo-mentum resolution of SA muons (and hence the corre-sponding dimuon invariant mass resolution – as shownin Fig. 15) is expected to be independent of the η ofthe decay muons, except in the magnet transition re-gion (1 . < | η | < .
7) where the magnetic field inthe MS is highly non-uniform, with a field integral ap-proaching 0 in certain ( η, φ ) regions [3]. Furthermore,some chambers in the region 1 . < | η | < . which means that the momentum mea-surement relies on only two layers of chambers, causinga significant degradation in the momentum resolution.Figure 15 also shows that the MS dimuon invariantmass resolution is consistently worse in data than insimulation (typically between 30% and 50% worse, de-pending on η region). Two sources for this effect wereidentified.1. Asymmetry of the magnetic field : in the MCsimulation, a perfectly aligned detector is assumed.In reality, the two end-cap toroid systems are notsymmetric with respect to the plane orthogonal tothe major axis of the ID, and situated at the cen-tre of the detector. This small asymmetry translatesinto an asymmetry of the magnetic field integrals, inparticular in the transition regions. The reconstruc-tion of the 2010 data with a corrected field mapimproves the dimuon invariant mass resolution inthe transition region by 0.4 GeV.2.
Residual misalignment of the muon cham-bers : even after the MS alignment procedures areapplied, residual misalignments remain, which limitthe attainable momentum resolution. The analysisof a special set of 2011 data with no magnetic fieldin the MS was used to produce a Monte Carlo simu-lation of Z → µ + µ − events with the addition of a re-alistic residual misalignment of the MS. The results This detector configuration was also used for the 2011 datataking.9 <− . η − . < <− . η − . < <− . η − . < < . η − . < < . η . < < . η . < < . η . < [ G e V ] Ζ r e s o l u t i on a t m µµ m = 7 TeVsID Tracks −1 L = 40 pb ∫ Data 2010Simulation
ATLAS <− . η − . < <− . η − . < <− . η − . < < . η − . < < . η . < < . η . < < . η . < [ G e V ] Ζ r e s o l u t i on a t m µµ m = 7 TeVsMS Tracks −1 L = 40 pb ∫ Data 2010Simulation
ATLAS
Fig. 15
The dimuon invariant mass ( m µµ ) resolutions in Z → µ + µ − decays in the data and in the MC as a function of η regionwith both decay muons in the same η region, for the ID (left) and MS (right). The simulation assumes a perfectly alignedATLAS detector. <− . η − . < <− . η − . < <− . η − . < < . η − . < < . η . < < . η . < < . η . < [ G e V ] Ζ r e s o l u t i on a t m µµ m = 7 TeVsCB Tracks −1 L = 40 pb ∫ Data 2010Simulation
ATLAS
Fig. 16
Dimuon invariant mass ( m µµ ) resolution for com-bined muons in Z → µ + µ − decays in the data and in the MCas a function of η region with both decay muons in the same η region. The simulation assumes a perfectly aligned ATLASdetector. of this simulation are in agreement with the exper-imentally determined invariant mass resolutions.The dimuon invariant mass resolution obtained withCB muons profits from the complementary momentum measurements of the ID and MS. As shown in Fig. 16,a dimuon invariant mass resolution between 1.4 GeVand 2.5 GeV is achieved, with little dependence on η .The measured dimuon invariant mass resolutionscan be translated into muon momentum resolutions.This was done by smearing the generated muon mo-menta, according to Eqs. (2) and (3), by the amountsnecessary to reproduce the measured dimuon invari-ant mass resolutions. Only the parameters b ID ( η ) and a MS ( η, φ ) were varied during this procedure. The pa-rameter a ID ( η ) was set to the Monte Carlo predictionand varied within its uncertainty (see above) to evalu-ate the impact on the result for b ID ( η ). The parameter b MS ( η, φ ) was set to the value derived from the spe-cial straight-track data set while c ( η, φ ) was set to itspredicted value. In order to gain additional sensitiv-ity to the momentum resolutions of the ID and MS,in addition to the dimuon mass spectrum of Z bosondecays, the distributions of the differences between theID and SA momenta of muons from W → µν µ decayswere compared between the experimental and smearedMC data. The W boson selection and the MC sam-ples for the analysis are the same as in Ref. [10]. Asthe use of W boson decays correlates the SA and IDresolutions, those are extracted simultaneously in thefit. The results are displayed for the different detectorregions in Figs. 17 and 18, with the uncertainty of thecurves computed from the uncertainties of the parame-ters in the resolution functions (Eqs. (2) and (3)). Also [GeV] T p0 20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<1.05 ) η Barrel ID ( |
Smeared SimulationExtrapolationSimulation [GeV] T p20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<1.05 ) η Barrel MS ( |
Smeared SimulationExtrapolationSimulation [GeV] T p0 20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<1.7 ) η Transition ID ( 1.05<|
Smeared SimulationExtrapolationSimulation [GeV] T p20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<1.7 ) η Transition MS ( 1.05<|
Smeared SimulationExtrapolationSimulation
Fig. 17
Muon momentum resolution as a function of p T for different barrel and transition | η | regions as denoted in the legend.The dot-dash line is from a simulation which assumes perfect alignment of the ATLAS detector, whilst the solid/dotted lineshows simulation smeared to reproduce the invariant mass resolution measured in data. The solid section of the line showsthe p T range measured by Z and W decays, and the dotted section the ‘extrapolation’ regions. The shaded bands show theuncertainty of the curves, computed from the uncertainties of the parameters derived in the resolution functions shown inEqs. (2) and (3). shown is the expected resolution beyond the region in p T probed by the Z -boson decays. As discussed ear-lier, the momentum resolution in experimental data isworse than in the Monte Carlo simulation, which is at-tributed, in part, to the residual misalignments of theID and MS.
11 Summary
The ATLAS muon reconstruction efficiencies were stud-ied with
J/ψ → µ + µ − and Z → µ + µ − decays using40 pb − of √ s = 7 TeV pp LHC collision data recordedin 2010. Samples of
J/ψ and Z decays were used to ac-cess the transverse momentum regions of p T <
10 GeVand 20 GeV < p T <
100 GeV respectively. The muon [GeV] T p0 20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<2.0 ) η End Cap ID ( 1.7<|
Smeared SimulationExtrapolationSimulation [GeV] T p20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<2.0 ) η End Cap MS ( 1.7<|
Smeared SimulationExtrapolationSimulation [GeV] θ /tan T p0 500 1000 1500 2000 2500 3000 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<2.5 ) η No TRT ID ( 2.0<|
Smeared SimulationExtrapolationSimulation [GeV] T p20 40 60 80 100 120 140 160 180 200 T ) / p T ( p σ = 7 TeVs −1 L = 40 pb ∫ ATLAS |<2.5 ) η CSC MS ( 2.0<|
Smeared SimulationExtrapolationSimulation
Fig. 18
Muon momentum resolutions as a function of p T for different end-cap | η | regions as denoted in the legend. For theID region | η | > . p T / tan ( θ ) instead of p T . The dot-dash line is simulation which assumes perfect alignment of the ATLAS detector, whilst the solid/dotted line shows simulationsmeared to reproduce the invariant mass resolution measured in data. The solid section of the line shows the p T range measuredby Z decays, and the dotted section the ‘extrapolation’ regions. The shaded bands show the uncertainty of the curves, whichare computed from the uncertainties of the parameters in the resolution functions shown in Eqs. (2) and (3). reconstruction efficiency is found to be >
96% andagrees with the MC prediction to better than 1%. Thereconstructed quantities used to ensure muon isolationare shown to be well modelled in Monte Carlo simula-tions, and the corresponding muon isolation efficienciesare in excellent agreement with the MC predictions.The muon momentum resolutions for p T >
20 GeVare derived from the dimuon mass resolutions in Z → µ + µ − decays and from the differences between the IDand SA momenta of muons from W → µν µ decays. Theresolutions are worse in data than in simulation forthe entire momentum range considered. For instance,at p T ≈
30 GeV and 1 . < | η | < . field and residual misalignments of the inner detectorand muon spectrometer. An improved magnetic fieldmap was used from 2011 onwards, and there have sincebeen several iterations of the alignment. Acknowledgements
We thank CERN for the very successful operation of theLHC, as well as the support staff from our institutionswithout whom ATLAS could not be operated efficiently.We acknowledge the support of ANPCyT, Argentina;YerPhI, Armenia; ARC, Australia; BMWF and FWF,Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq andFAPESP, Brazil; NSERC, NRC and CFI, Canada;CERN; CONICYT, Chile; CAS, MOST and NSFC, Chi-na; COLCIENCIAS, Colombia; MSMT CR, MPO CRand VSC CR, Czech Republic; DNRF, DNSRC andLundbeck Foundation, Denmark; EPLANET, ERC andNSRF, European Union; IN2P3-CNRS, CEA-DSM/IR-FU, France; GNSF, Georgia; BMBF, DFG, HGF, MPGand AvH Foundation, Germany; GSRT and NSRF,Greece; ISF, MINERVA, GIF, I-CORE and BenoziyoCenter, Israel; INFN, Italy; MEXT and JSPS, Japan;CNRST, Morocco; FOM and NWO, Netherlands; BRFand RCN, Norway; MNiSW and NCN, Poland; GRICESand FCT, Portugal; MNE/IFA, Romania; MES of Rus-sia and ROSATOM, Russian Federation; JINR; MSTD,Serbia; MSSR, Slovakia; ARRS and MIZˇS, Slovenia;DST/NRF, South Africa; MINECO, Spain; SRC andWallenberg Foundation, Sweden; SER, SNSF and Can-tons of Bern and Geneva, Switzerland; NSC, Taiwan;TAEK, Turkey; STFC, the Royal Society and Lever-hulme Trust, United Kingdom; DOE and NSF, UnitedStates of America.The crucial computing support from all WLCG part-ners is acknowledged gratefully, in particular fromCERN and the ATLAS Tier-1 facilities at TRIUMF(Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF(Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Tai-wan), RAL (UK) and BNL (USA) and in the Tier-2facilities worldwide.
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Gonzalez Parra , M.L. Gonzalez Silva , S. Gonzalez-Sevilla , J.J. Goodson , L. Goossens ,P.A. Gorbounov , H.A. Gordon , I. Gorelov , G. Gorfine , B. Gorini , E. Gorini , , A. Goriˇsek ,E. Gornicki , B. Gosdzik , A.T. Goshaw , M. Gosselink , M.I. Gostkin , I. Gough Eschrich ,M. Gouighri , D. Goujdami , M.P. Goulette , A.G. Goussiou , C. Goy , S. Gozpinar ,I. Grabowska-Bold , P. Grafstr¨om , , K-J. Grahn , F. Grancagnolo , S. Grancagnolo , V. Grassi ,V. Gratchev , N. Grau , H.M. Gray , J.A. Gray , E. Graziani , O.G. Grebenyuk , T. Greenshaw ,Z.D. Greenwood ,m , K. Gregersen , I.M. Gregor , P. Grenier , J. Griffiths , N. Grigalashvili ,A.A. Grillo , S. Grinstein , Y.V. Grishkevich , J.-F. Grivaz , E. Gross , J. Grosse-Knetter ,J. Groth-Jensen , K. Grybel , D. Guest , C. Guicheney , S. Guindon , U. Gul , H. Guler ,p ,J. Gunther , B. Guo , J. Guo , P. Gutierrez , N. Guttman , O. Gutzwiller , C. Guyot ,C. Gwenlan , C.B. Gwilliam , A. Haas , S. Haas , C. Haber , H.K. Hadavand , D.R. Hadley ,P. Haefner , F. Hahn , S. Haider , Z. Hajduk , H. Hakobyan , D. Hall , J. Haller , K. Hamacher ,P. Hamal , M. Hamer , A. Hamilton ,q , S. Hamilton , L. Han , K. Hanagaki , K. Hanawa ,M. Hance , C. Handel , P. Hanke , J.R. Hansen , J.B. Hansen , J.D. Hansen , P.H. Hansen ,P. Hansson , K. Hara , G.A. Hare , T. Harenberg , S. Harkusha , D. Harper , R.D. Harrington ,O.M. Harris , J. Hartert , F. Hartjes , T. Haruyama , A. Harvey , S. Hasegawa , Y. Hasegawa ,S. Hassani , S. Haug , M. Hauschild , R. Hauser , M. Havranek , C.M. Hawkes , R.J. Hawkings ,A.D. Hawkins , D. Hawkins , T. Hayakawa , T. Hayashi , D. Hayden , C.P. Hays , H.S. Hayward ,S.J. Haywood , M. He , S.J. Head , V. Hedberg , L. Heelan , S. Heim , B. Heinemann , S. Heisterkamp , L. Helary , C. Heller , M. Heller , S. Hellman , , D. Hellmich , C. Helsens ,R.C.W. Henderson , M. Henke , A. Henrichs , A.M. Henriques Correia , S. Henrot-Versille , C. Hensel ,T. Henß , C.M. Hernandez , Y. Hern´andez Jim´enez , R. Herrberg , G. Herten , R. Hertenberger ,L. Hervas , G.G. Hesketh , N.P. Hessey , E. Hig´on-Rodriguez , J.C. Hill , K.H. Hiller , S. Hillert ,S.J. Hillier , I. Hinchliffe , E. Hines , M. Hirose , F. Hirsch , D. Hirschbuehl , J. Hobbs , N. Hod ,M.C. Hodgkinson , P. Hodgson , A. Hoecker , M.R. Hoeferkamp , J. Hoffman , D. Hoffmann ,M. Hohlfeld , M. Holder , S.O. Holmgren , T. Holy , J.L. Holzbauer , T.M. Hong ,L. Hooft van Huysduynen , C. Horn , S. Horner , J-Y. Hostachy , S. Hou , A. Hoummada ,J. Howard , J. Howarth , I. Hristova , J. Hrivnac , T. Hryn’ova , P.J. Hsu , S.-C. Hsu , Z. Hubacek ,F. Hubaut , F. Huegging , A. Huettmann , T.B. Huffman , E.W. Hughes , G. Hughes , M. Huhtinen ,M. Hurwitz , U. Husemann , N. Huseynov ,r , J. Huston , J. Huth , G. Iacobucci , G. Iakovidis ,M. Ibbotson , I. Ibragimov , L. Iconomidou-Fayard , J. Idarraga , P. Iengo , O. Igonkina ,Y. Ikegami , M. Ikeno , D. Iliadis , N. Ilic , T. Ince , J. Inigo-Golfin , P. Ioannou , M. Iodice ,K. Iordanidou , V. Ippolito , , A. Irles Quiles , C. Isaksson , M. Ishino , M. Ishitsuka ,R. Ishmukhametov , C. Issever , S. Istin , A.V. Ivashin , W. Iwanski , H. Iwasaki , J.M. Izen ,V. Izzo , B. Jackson , J.N. Jackson , P. Jackson , M.R. Jaekel , V. Jain , K. Jakobs , S. Jakobsen ,T. Jakoubek , J. Jakubek , D.K. Jana , E. Jansen , H. Jansen , A. Jantsch , M. Janus , G. Jarlskog ,L. Jeanty , I. Jen-La Plante , D. Jennens , P. Jenni , A.E. Loevschall-Jensen , P. Jeˇ z , S. J´ez´equel ,M.K. Jha , H. Ji , W. Ji , J. Jia , Y. Jiang , M. Jimenez Belenguer , S. Jin , O. Jinnouchi ,M.D. Joergensen , D. Joffe , M. Johansen , , K.E. Johansson , P. Johansson , S. Johnert ,K.A. Johns , K. Jon-And , , G. Jones , R.W.L. Jones , T.J. Jones , C. Joram , P.M. Jorge ,K.D. Joshi , J. Jovicevic , T. Jovin , X. Ju , C.A. Jung , R.M. Jungst , V. Juranek , P. Jussel ,A. Juste Rozas , S. Kabana , M. Kaci , A. Kaczmarska , P. Kadlecik , M. Kado , H. Kagan ,M. Kagan , E. Kajomovitz , S. Kalinin , L.V. Kalinovskaya , S. Kama , N. Kanaya , M. Kaneda ,S. Kaneti , T. Kanno , V.A. Kantserov , J. Kanzaki , B. Kaplan , A. Kapliy , J. Kaplon , D. Kar ,M. Karagounis , K. Karakostas , M. Karnevskiy , V. Kartvelishvili , A.N. Karyukhin , L. Kashif ,G. Kasieczka , R.D. Kass , A. Kastanas , M. Kataoka , Y. Kataoka , E. Katsoufis , J. Katzy ,V. Kaushik , K. Kawagoe , T. Kawamoto , G. Kawamura , M.S. Kayl , S. Kazama , V.A. Kazanin ,M.Y. Kazarinov , R. Keeler , R. Kehoe , M. Keil , G.D. Kekelidze , J.S. Keller , M. Kenyon ,O. Kepka , N. Kerschen , B.P. Kerˇsevan , S. Kersten , K. Kessoku , J. Keung , F. Khalil-zada ,H. Khandanyan , A. Khanov , D. Kharchenko , A. Khodinov , A. Khomich , T.J. Khoo ,G. Khoriauli , A. Khoroshilov , V. Khovanskiy , E. Khramov , J. Khubua , H. Kim , , S.H. Kim ,N. Kimura , O. Kind , B.T. King , M. King , R.S.B. King , J. Kirk , A.E. Kiryunin , T. Kishimoto ,D. Kisielewska , T. Kitamura , T. Kittelmann , E. Kladiva , M. Klein , U. Klein , K. Kleinknecht ,M. Klemetti , A. Klier , P. Klimek , , A. Klimentov , R. Klingenberg , J.A. Klinger ,E.B. Klinkby , T. Klioutchnikova , P.F. Klok , S. Klous , E.-E. Kluge , T. Kluge , P. Kluit ,S. Kluth , N.S. Knecht , E. Kneringer , E.B.F.G. Knoops , A. Knue , B.R. Ko , T. Kobayashi ,M. Kobel , M. Kocian , P. Kodys , K. K¨oneke , A.C. K¨onig , S. Koenig , L. K¨opke , F. Koetsveld ,P. Koevesarki , T. Koffas , E. Koffeman , L.A. Kogan , S. Kohlmann , F. Kohn , Z. Kohout ,T. Kohriki , T. Koi , G.M. Kolachev , ∗ , H. Kolanoski , V. Kolesnikov , I. Koletsou , J. Koll ,M. Kollefrath , A.A. Komar , Y. Komori , T. Kondo , T. Kono ,s , A.I. Kononov , R. Konoplich ,t ,N. Konstantinidis , S. Koperny , K. Korcyl , K. Kordas , A. Korn , A. Korol , I. Korolkov ,E.V. Korolkova , V.A. Korotkov , O. Kortner , S. Kortner , V.V. Kostyukhin , S. Kotov ,V.M. Kotov , A. Kotwal , C. Kourkoumelis , V. Kouskoura , A. Koutsman , R. Kowalewski ,T.Z. Kowalski , W. Kozanecki , A.S. Kozhin , V. Kral , V.A. Kramarenko , G. Kramberger ,M.W. Krasny , A. Krasznahorkay , J.K. Kraus , S. Kreiss , F. Krejci , J. Kretzschmar , N. Krieger ,P. Krieger , K. Kroeninger , H. Kroha , J. Kroll , J. Kroseberg , J. Krstic , U. Kruchonak ,H. Kr¨uger , T. Kruker , N. Krumnack , Z.V. Krumshteyn , T. Kubota , S. Kuday , S. Kuehn ,A. Kugel , T. Kuhl , D. Kuhn , V. Kukhtin , Y. Kulchitsky , S. Kuleshov , C. Kummer , M. Kuna ,J. Kunkle , A. Kupco , H. Kurashige , M. Kurata , Y.A. Kurochkin , V. Kus , E.S. Kuwertz ,M. Kuze , J. Kvita , R. Kwee , A. La Rosa , L. La Rotonda , , L. Labarga , J. Labbe , S. Lablak ,C. Lacasta , F. Lacava , , H. Lacker , D. Lacour , V.R. Lacuesta , E. Ladygin , R. Lafaye ,B. Laforge , T. Lagouri , S. Lai , E. Laisne , M. Lamanna , L. Lambourne , C.L. Lampen , W. Lampl , E. Lancon , U. Landgraf , M.P.J. Landon , J.L. Lane , V.S. Lang , C. Lange , A.J. Lankford ,F. Lanni , K. Lantzsch , S. Laplace , C. Lapoire , J.F. Laporte , T. Lari , A. Larner , M. Lassnig ,P. Laurelli , V. Lavorini , , W. Lavrijsen , P. Laycock , O. Le Dortz , E. Le Guirriec , C. Le Maner ,E. Le Menedeu , T. LeCompte , F. Ledroit-Guillon , H. Lee , J.S.H. Lee , S.C. Lee , L. Lee ,M. Lefebvre , M. Legendre , F. Legger , C. Leggett , M. Lehmacher , G. Lehmann Miotto , X. Lei ,M.A.L. Leite , R. Leitner , D. Lellouch , B. Lemmer , V. Lendermann , K.J.C. Leney , T. Lenz ,G. Lenzen , B. Lenzi , K. Leonhardt , S. Leontsinis , F. Lepold , C. Leroy , J-R. Lessard ,C.G. Lester , C.M. Lester , J. Levˆeque , D. Levin , L.J. Levinson , A. Lewis , G.H. Lewis ,A.M. Leyko , M. Leyton , B. Li , H. Li ,u , S. Li ,v , X. Li , Z. Liang ,w , H. Liao , B. Liberti ,P. Lichard , M. Lichtnecker , K. Lie , W. Liebig , C. Limbach , A. Limosani , M. Limper , S.C. Lin ,x ,F. Linde , J.T. Linnemann , E. Lipeles , A. Lipniacka , T.M. Liss , D. Lissauer , A. Lister ,A.M. Litke , C. Liu , D. Liu , H. Liu , J.B. Liu , L. Liu , M. Liu , Y. Liu , M. Livan , ,S.S.A. Livermore , A. Lleres , J. Llorente Merino , S.L. Lloyd , E. Lobodzinska , P. Loch ,W.S. Lockman , T. Loddenkoetter , F.K. Loebinger , A. Loginov , C.W. Loh , T. Lohse ,K. Lohwasser , M. Lokajicek , V.P. Lombardo , R.E. Long , L. Lopes , D. Lopez Mateos , J. Lorenz ,N. Lorenzo Martinez , M. Losada , P. Loscutoff , F. Lo Sterzo , , M.J. Losty , X. Lou ,A. Lounis , K.F. Loureiro , J. Love , P.A. Love , A.J. Lowe ,e , F. Lu , H.J. Lubatti , C. Luci , ,A. Lucotte , A. Ludwig , D. Ludwig , I. Ludwig , J. Ludwig , F. Luehring , G. Luijckx , W. Lukas ,D. Lumb , L. Luminari , E. Lund , B. Lund-Jensen , B. Lundberg , J. Lundberg , ,O. Lundberg , , J. Lundquist , M. Lungwitz , D. Lynn , E. Lytken , H. Ma , L.L. Ma ,G. Maccarrone , A. Macchiolo , B. Maˇcek , J. Machado Miguens , R. Mackeprang , R.J. Madaras ,H.J. Maddocks , W.F. Mader , R. Maenner , T. Maeno , P. M¨attig , S. M¨attig , L. Magnoni ,E. Magradze , K. Mahboubi , S. Mahmoud , G. Mahout , C. Maiani , C. Maidantchik , A. Maio ,b ,S. Majewski , Y. Makida , N. Makovec , P. Mal , B. Malaescu , Pa. Malecki , P. Malecki ,V.P. Maleev , F. Malek , U. Mallik , D. Malon , C. Malone , S. Maltezos , V. Malyshev , S. Malyukov ,R. Mameghani , J. Mamuzic , A. Manabe , L. Mandelli , I. Mandi´c , R. Mandrysch , J. Maneira ,P.S. Mangeard , L. Manhaes de Andrade Filho , J.A. Manjarres Ramos , A. Mann , P.M. Manning ,A. Manousakis-Katsikakis , B. Mansoulie , A. Mapelli , L. Mapelli , L. March , J.F. Marchand ,F. Marchese , , G. Marchiori , M. Marcisovsky , C.P. Marino , F. Marroquim , Z. Marshall ,F.K. Martens , L.F. Marti , S. Marti-Garcia , B. Martin , B. Martin , J.P. Martin , T.A. Martin ,V.J. Martin , B. Martin dit Latour , S. Martin-Haugh , M. Martinez , V. Martinez Outschoorn ,A.C. Martyniuk , M. Marx , F. Marzano , A. Marzin , L. Masetti , T. Mashimo , R. Mashinistov ,J. Masik , A.L. Maslennikov , I. Massa , , G. Massaro , N. Massol , P. Mastrandrea ,A. Mastroberardino , , T. Masubuchi , P. Matricon , H. Matsunaga , T. Matsushita ,C. Mattravers ,c , J. Maurer , S.J. Maxfield , A. Mayne , R. Mazini , M. Mazur , L. Mazzaferro , ,M. Mazzanti , S.P. Mc Kee , A. McCarn , R.L. McCarthy , T.G. McCarthy , N.A. McCubbin ,K.W. McFarlane , ∗ , J.A. Mcfayden , G. Mchedlidze , T. Mclaughlan , S.J. McMahon ,R.A. McPherson ,k , A. Meade , J. Mechnich , M. Mechtel , M. Medinnis , R. Meera-Lebbai ,T. Meguro , R. Mehdiyev , S. Mehlhase , A. Mehta , K. Meier , B. Meirose , C. Melachrinos ,B.R. Mellado Garcia , F. Meloni , , L. Mendoza Navas , Z. Meng ,u , A. Mengarelli , , S. Menke ,E. Meoni , K.M. Mercurio , P. Mermod , L. Merola , , C. Meroni , F.S. Merritt , H. Merritt ,A. Messina ,y , J. Metcalfe , A.S. Mete , C. Meyer , C. Meyer , J-P. Meyer , J. Meyer , J. Meyer ,T.C. Meyer , J. Miao , S. Michal , L. Micu , R.P. Middleton , S. Migas , L. Mijovi´c ,G. Mikenberg , M. Mikestikova , M. Mikuˇz , D.W. Miller , R.J. Miller , W.J. Mills , C. Mills ,A. Milov , D.A. Milstead , , D. Milstein , A.A. Minaenko , M. Mi˜nano Moya , I.A. Minashvili ,A.I. Mincer , B. Mindur , M. Mineev , Y. Ming , L.M. Mir , G. Mirabelli , J. Mitrevski ,V.A. Mitsou , S. Mitsui , P.S. Miyagawa , J.U. Mj¨ornmark , T. Moa , , V. Moeller , K. M¨onig ,N. M¨oser , S. Mohapatra , W. Mohr , R. Moles-Valls , J. Monk , E. Monnier , J. Montejo Berlingen ,F. Monticelli , S. Monzani , , R.W. Moore , G.F. Moorhead , C. Mora Herrera , A. Moraes ,N. Morange , J. Morel , G. Morello , , D. Moreno , M. Moreno Ll´acer , P. Morettini ,M. Morgenstern , M. Morii , A.K. Morley , G. Mornacchi , J.D. Morris , L. Morvaj , H.G. Moser ,M. Mosidze , J. Moss , R. Mount , E. Mountricha ,z , S.V. Mouraviev , ∗ , E.J.W. Moyse , F. Mueller ,J. Mueller , K. Mueller , T.A. M¨uller , T. Mueller , D. Muenstermann , Y. Munwes , W.J. Murray , I. Mussche , E. Musto , , A.G. Myagkov , M. Myska , J. Nadal , K. Nagai , R. Nagai ,K. Nagano , A. Nagarkar , Y. Nagasaka , M. Nagel , A.M. Nairz , Y. Nakahama , K. Nakamura ,T. Nakamura , I. Nakano , G. Nanava , A. Napier , R. Narayan , M. Nash ,c , T. Nattermann ,T. Naumann , G. Navarro , H.A. Neal , P.Yu. Nechaeva , T.J. Neep , A. Negri , , G. Negri ,M. Negrini , S. Nektarijevic , A. Nelson , T.K. Nelson , S. Nemecek , P. Nemethy ,A.A. Nepomuceno , M. Nessi ,aa , M.S. Neubauer , M. Neumann , A. Neusiedl , R.M. Neves ,P. Nevski , P.R. Newman , V. Nguyen Thi Hong , R.B. Nickerson , R. Nicolaidou , B. Nicquevert ,F. Niedercorn , J. Nielsen , N. Nikiforou , A. Nikiforov , V. Nikolaenko , I. Nikolic-Audit ,K. Nikolics , K. Nikolopoulos , H. Nilsen , P. Nilsson , Y. Ninomiya , A. Nisati , R. Nisius ,T. Nobe , L. Nodulman , M. Nomachi , I. Nomidis , S. Norberg , M. Nordberg , P.R. Norton ,J. Novakova , M. Nozaki , L. Nozka , I.M. Nugent , A.-E. Nuncio-Quiroz , G. Nunes Hanninger ,T. Nunnemann , E. Nurse , B.J. O’Brien , S.W. O’Neale , ∗ , D.C. O’Neil , V. O’Shea , L.B. Oakes ,F.G. Oakham ,d , H. Oberlack , J. Ocariz , A. Ochi , S. Oda , S. Odaka , J. Odier , H. Ogren , A. Oh ,S.H. Oh , C.C. Ohm , T. Ohshima , H. Okawa , Y. Okumura , T. Okuyama , A. Olariu ,A.G. Olchevski , S.A. Olivares Pino , M. Oliveira ,h , D. Oliveira Damazio , E. Oliver Garcia ,D. Olivito , A. Olszewski , J. Olszowska , A. Onofre ,ab , P.U.E. Onyisi , C.J. Oram , M.J. Oreglia ,Y. Oren , D. Orestano , , N. Orlando , , I. Orlov , C. Oropeza Barrera , R.S. Orr ,B. Osculati , , R. Ospanov , C. Osuna , G. Otero y Garzon , J.P. Ottersbach , M. Ouchrif ,E.A. Ouellette , F. Ould-Saada , A. Ouraou , Q. Ouyang , A. Ovcharova , M. Owen , S. Owen ,V.E. Ozcan , N. Ozturk , A. Pacheco Pages , C. Padilla Aranda , S. Pagan Griso , E. Paganis ,C. Pahl , F. Paige , P. Pais , K. Pajchel , G. Palacino , C.P. Paleari , S. Palestini , D. Pallin ,A. Palma , J.D. Palmer , Y.B. Pan , E. Panagiotopoulou , P. Pani , N. Panikashvili , S. Panitkin ,D. Pantea , A. Papadelis , Th.D. Papadopoulou , A. Paramonov , D. Paredes Hernandez , W. Park ,ac ,M.A. Parker , F. Parodi , , J.A. Parsons , U. Parzefall , S. Pashapour , E. Pasqualucci ,S. Passaggio , A. Passeri , F. Pastore , , ∗ , Fr. Pastore , G. P´asztor ,ad , S. Pataraia , N. Patel ,J.R. Pater , S. Patricelli , , T. Pauly , M. Pecsy , S. Pedraza Lopez , M.I. Pedraza Morales ,S.V. Peleganchuk , D. Pelikan , H. Peng , B. Penning , A. Penson , J. Penwell , M. Perantoni ,K. Perez ,ae , T. Perez Cavalcanti , E. Perez Codina , M.T. P´erez Garc´ıa-Esta˜n , V. Perez Reale ,L. Perini , , H. Pernegger , R. Perrino , P. Perrodo , V.D. Peshekhonov , K. Peters , B.A. Petersen ,J. Petersen , T.C. Petersen , E. Petit , A. Petridis , C. Petridou , E. Petrolo , F. Petrucci , ,D. Petschull , M. Petteni , R. Pezoa , A. Phan , P.W. Phillips , G. Piacquadio , A. Picazio ,E. Piccaro , M. Piccinini , , S.M. Piec , R. Piegaia , D.T. Pignotti , J.E. Pilcher , A.D. Pilkington ,J. Pina ,b , M. Pinamonti , , A. Pinder , J.L. Pinfold , B. Pinto , C. Pizio , , M. Plamondon ,M.-A. Pleier , E. Plotnikova , A. Poblaguev , S. Poddar , F. Podlyski , L. Poggioli , M. Pohl ,G. Polesello , A. Policicchio , , A. Polini , J. Poll , V. Polychronakos , D. Pomeroy , K. Pomm`es ,L. Pontecorvo , B.G. Pope , G.A. Popeneciu , D.S. Popovic , A. Poppleton , X. Portell Bueso ,G.E. Pospelov , S. Pospisil , I.N. Potrap , C.J. Potter , C.T. Potter , G. Poulard , J. Poveda ,V. Pozdnyakov , R. Prabhu , P. Pralavorio , A. Pranko , S. Prasad , R. Pravahan , S. Prell , K. Pretzl ,D. Price , J. Price , L.E. Price , D. Prieur , M. Primavera , K. Prokofiev , F. Prokoshin ,S. Protopopescu , J. Proudfoot , X. Prudent , M. Przybycien , H. Przysiezniak , S. Psoroulas ,E. Ptacek , E. Pueschel , J. Purdham , M. Purohit ,ac , P. Puzo , Y. Pylypchenko , J. Qian ,A. Quadt , D.R. Quarrie , W.B. Quayle , F. Quinonez , M. Raas , V. Radescu , P. Radloff ,T. Rador , F. Ragusa , , G. Rahal , A.M. Rahimi , D. Rahm , S. Rajagopalan , M. Rammensee ,M. Rammes , A.S. Randle-Conde , K. Randrianarivony , F. Rauscher , T.C. Rave , M. Raymond ,A.L. Read , D.M. Rebuzzi , , A. Redelbach , G. Redlinger , R. Reece , K. Reeves ,E. Reinherz-Aronis , A. Reinsch , H. Reisin , I. Reisinger , C. Rembser , Z.L. Ren , A. Renaud ,M. Rescigno , S. Resconi , B. Resende , P. Reznicek , R. Rezvani , R. Richter , E. Richter-Was ,af ,M. Ridel , M. Rijpstra , M. Rijssenbeek , A. Rimoldi , , L. Rinaldi , R.R. Rios , I. Riu ,G. Rivoltella , , F. Rizatdinova , E. Rizvi , S.H. Robertson ,k , A. Robichaud-Veronneau ,D. Robinson , J.E.M. Robinson , A. Robson , J.G. Rocha de Lima , C. Roda , ,D. Roda Dos Santos , A. Roe , S. Roe , O. Røhne , S. Rolli , A. Romaniouk , M. Romano , ,G. Romeo , E. Romero Adam , L. Roos , E. Ros , S. Rosati , K. Rosbach , A. Rose , M. Rose ,G.A. Rosenbaum , E.I. Rosenberg , P.L. Rosendahl , O. Rosenthal , L. Rosselet , V. Rossetti , E. Rossi , , L.P. Rossi , M. Rotaru , I. Roth , J. Rothberg , D. Rousseau , C.R. Royon ,A. Rozanov , Y. Rozen , X. Ruan ,ag , F. Rubbo , I. Rubinskiy , N. Ruckstuhl , V.I. Rud ,C. Rudolph , G. Rudolph , F. R¨uhr , A. Ruiz-Martinez , L. Rumyantsev , Z. Rurikova ,N.A. Rusakovich , J.P. Rutherfoord , C. Ruwiedel , ∗ , P. Ruzicka , Y.F. Ryabov , M. Rybar ,G. Rybkin , N.C. Ryder , A.F. Saavedra , S. Sacerdoti , I. Sadeh , H.F-W. Sadrozinski ,R. Sadykov , F. Safai Tehrani , H. Sakamoto , G. Salamanna , A. Salamon , M. Saleem , D. Salek ,D. Salihagic , A. Salnikov , J. Salt , B.M. Salvachua Ferrando , D. Salvatore , , F. Salvatore ,A. Salvucci , A. Salzburger , D. Sampsonidis , B.H. Samset , A. Sanchez , ,V. Sanchez Martinez , H. Sandaker , H.G. Sander , M.P. Sanders , M. Sandhoff , T. Sandoval ,C. Sandoval , R. Sandstroem , D.P.C. Sankey , A. Sansoni , C. Santamarina Rios , C. Santoni ,R. Santonico , , H. Santos , J.G. Saraiva , T. Sarangi , E. Sarkisyan-Grinbaum , F. Sarri , ,G. Sartisohn , O. Sasaki , Y. Sasaki , N. Sasao , I. Satsounkevitch , G. Sauvage , ∗ , E. Sauvan ,J.B. Sauvan , P. Savard ,d , V. Savinov , D.O. Savu , L. Sawyer ,m , D.H. Saxon , J. Saxon ,C. Sbarra , A. Sbrizzi , , D.A. Scannicchio , M. Scarcella , J. Schaarschmidt , P. Schacht ,D. Schaefer , U. Sch¨afer , S. Schaepe , S. Schaetzel , A.C. Schaffer , D. Schaile , R.D. Schamberger ,A.G. Schamov , V. Scharf , V.A. Schegelsky , D. Scheirich , M. Schernau , M.I. Scherzer ,C. Schiavi , , J. Schieck , M. Schioppa , , S. Schlenker , E. Schmidt , K. Schmieden , C. Schmitt ,S. Schmitt , M. Schmitz , B. Schneider , U. Schnoor , A. Schoening , A.L.S. Schorlemmer , M. Schott ,D. Schouten , J. Schovancova , M. Schram , C. Schroeder , N. Schroer , M.J. Schultens ,J. Schultes , H.-C. Schultz-Coulon , H. Schulz , M. Schumacher , B.A. Schumm , Ph. Schune ,C. Schwanenberger , A. Schwartzman , Ph. Schwemling , R. Schwienhorst , R. Schwierz ,J. Schwindling , T. Schwindt , M. Schwoerer , G. Sciolla , W.G. Scott , J. Searcy , G. Sedov ,E. Sedykh , S.C. Seidel , A. Seiden , F. Seifert , J.M. Seixas , G. Sekhniaidze , S.J. Sekula ,K.E. Selbach , D.M. Seliverstov , B. Sellden , G. Sellers , M. Seman , N. Semprini-Cesari , ,C. Serfon , L. Serin , L. Serkin , R. Seuster , H. Severini , A. Sfyrla , E. Shabalina , M. Shamim ,L.Y. Shan , J.T. Shank , Q.T. Shao , M. Shapiro , P.B. Shatalov , K. Shaw , , D. Sherman ,P. Sherwood , A. Shibata , S. Shimizu , M. Shimojima , T. Shin , M. Shiyakova , A. Shmeleva ,M.J. Shochet , D. Short , S. Shrestha , E. Shulga , M.A. Shupe , P. Sicho , A. Sidoti , F. Siegert ,Dj. Sijacki , O. Silbert , J. Silva , Y. Silver , D. Silverstein , S.B. Silverstein , V. Simak ,O. Simard , Lj. Simic , S. Simion , E. Simioni , B. Simmons , R. Simoniello , , M. Simonyan ,P. Sinervo , N.B. Sinev , V. Sipica , G. Siragusa , A. Sircar , A.N. Sisakyan , ∗ , S.Yu. Sivoklokov ,J. Sj¨olin , , T.B. Sjursen , L.A. Skinnari , H.P. Skottowe , K. Skovpen , P. Skubic , M. Slater ,T. Slavicek , K. Sliwa , V. Smakhtin , B.H. Smart , S.Yu. Smirnov , Y. Smirnov , L.N. Smirnova ,O. Smirnova , B.C. Smith , D. Smith , K.M. Smith , M. Smizanska , K. Smolek , A.A. Snesarev ,S.W. Snow , J. Snow , S. Snyder , R. Sobie ,k , J. Sodomka , A. Soffer , C.A. Solans , M. Solar ,J. Solc , E.Yu. Soldatov , U. Soldevila , E. Solfaroli Camillocci , , A.A. Solodkov ,O.V. Solovyanov , V. Solovyev , N. Soni , V. Sopko , B. Sopko , M. Sosebee , R. Soualah , ,A. Soukharev , S. Spagnolo , , F. Span`o , R. Spighi , G. Spigo , R. Spiwoks , M. Spousta ,ah ,T. Spreitzer , B. Spurlock , R.D. St. Denis , J. Stahlman , R. Stamen , E. Stanecka , R.W. Stanek ,C. Stanescu , M. Stanescu-Bellu , S. Stapnes , E.A. Starchenko , J. Stark , P. Staroba ,P. Starovoitov , R. Staszewski , A. Staude , P. Stavina , ∗ , G. Steele , P. Steinbach , P. Steinberg ,I. Stekl , B. Stelzer , H.J. Stelzer , O. Stelzer-Chilton , H. Stenzel , S. Stern , G.A. Stewart ,J.A. Stillings , M.C. Stockton , K. Stoerig , G. Stoicea , S. Stonjek , P. Strachota , A.R. Stradling ,A. Straessner , J. Strandberg , S. Strandberg , , A. Strandlie , M. Strang , E. Strauss ,M. Strauss , P. Strizenec , R. Str¨ohmer , D.M. Strom , J.A. Strong , ∗ , R. Stroynowski , J. Strube ,B. Stugu , I. Stumer , ∗ , J. Stupak , P. Sturm , N.A. Styles , D.A. Soh ,w , D. Su , HS. Subramania ,A. Succurro , Y. Sugaya , C. Suhr , M. Suk , V.V. Sulin , S. Sultansoy , T. Sumida , X. Sun ,J.E. Sundermann , K. Suruliz , G. Susinno , , M.R. Sutton , Y. Suzuki , Y. Suzuki , M. Svatos ,S. Swedish , I. Sykora , T. Sykora , J. S´anchez , D. Ta , K. Tackmann , A. Taffard ,R. Tafirout , N. Taiblum , Y. Takahashi , H. Takai , R. Takashima , H. Takeda , T. Takeshita ,Y. Takubo , M. Talby , A. Talyshev ,f , M.C. Tamsett , J. Tanaka , R. Tanaka , S. Tanaka ,S. Tanaka , A.J. Tanasijczuk , K. Tani , N. Tannoury , S. Tapprogge , D. Tardif , S. Tarem ,F. Tarrade , G.F. Tartarelli , P. Tas , M. Tasevsky , E. Tassi , , M. Tatarkhanov , Y. Tayalati , C. Taylor , F.E. Taylor , G.N. Taylor , W. Taylor , M. Teinturier , M. Teixeira Dias Castanheira ,P. Teixeira-Dias , K.K. Temming , H. Ten Kate , P.K. Teng , S. Terada , K. Terashi , J. Terron ,M. Testa , R.J. Teuscher ,k , J. Therhaag , T. Theveneaux-Pelzer , S. Thoma , J.P. Thomas ,E.N. Thompson , P.D. Thompson , P.D. Thompson , A.S. Thompson , L.A. Thomsen , E. Thomson ,M. Thomson , W.M. Thong , R.P. Thun , F. Tian , M.J. Tibbetts , T. Tic , V.O. Tikhomirov ,Y.A. Tikhonov ,f , S. Timoshenko , P. Tipton , S. Tisserant , T. Todorov , S. Todorova-Nova ,B. Toggerson , J. Tojo , S. Tok´ar , K. Tokushuku , K. Tollefson , M. Tomoto , L. Tompkins ,K. Toms , A. Tonoyan , C. Topfel , N.D. Topilin , I. Torchiani , E. Torrence , H. Torres ,E. Torr´o Pastor , J. Toth ,ad , F. Touchard , D.R. Tovey , T. Trefzger , L. Tremblet , A. Tricoli ,I.M. Trigger , S. Trincaz-Duvoid , M.F. Tripiana , N. Triplett , W. Trischuk , B. Trocm´e ,C. Troncon , M. Trottier-McDonald , M. Trzebinski , A. Trzupek , C. Tsarouchas , J.C-L. Tseng ,M. Tsiakiris , P.V. Tsiareshka , D. Tsionou ,ai , G. Tsipolitis , S. Tsiskaridze , V. Tsiskaridze ,E.G. Tskhadadze , I.I. Tsukerman , V. Tsulaia , J.-W. Tsung , S. Tsuno , D. Tsybychev , A. Tua ,A. Tudorache , V. Tudorache , J.M. Tuggle , M. Turala , D. Turecek , I. Turk Cakir , E. Turlay ,R. Turra , , P.M. Tuts , A. Tykhonov , M. Tylmad , , M. Tyndel , G. Tzanakos , K. Uchida ,I. Ueda , R. Ueno , M. Ugland , M. Uhlenbrock , M. Uhrmacher , F. Ukegawa , G. Unal , A. Undrus ,G. Unel , Y. Unno , D. Urbaniec , G. Usai , M. Uslenghi , , L. Vacavant , V. Vacek , B. Vachon ,S. Vahsen , J. Valenta , S. Valentinetti , , A. Valero , S. Valkar , E. Valladolid Gallego ,S. Vallecorsa , J.A. Valls Ferrer , P.C. Van Der Deijl , R. van der Geer , H. van der Graaf ,R. Van Der Leeuw , E. van der Poel , D. van der Ster , N. van Eldik , P. van Gemmeren , I. van Vulpen ,M. Vanadia , W. Vandelli , A. Vaniachine , P. Vankov , F. Vannucci , R. Vari , T. Varol ,D. Varouchas , A. Vartapetian , K.E. Varvell , V.I. Vassilakopoulos , F. Vazeille , T. Vazquez Schroeder ,G. Vegni , , J.J. Veillet , F. Veloso , R. Veness , S. Veneziano , A. Ventura , , D. Ventura ,M. Venturi , N. Venturi , V. Vercesi , M. Verducci , W. Verkerke , J.C. Vermeulen , A. Vest ,M.C. Vetterli ,d , I. Vichou , T. Vickey ,aj , O.E. Vickey Boeriu , G.H.A. Viehhauser , S. Viel ,M. Villa , , M. Villaplana Perez , E. Vilucchi , M.G. Vincter , E. Vinek , V.B. Vinogradov ,M. Virchaux , ∗ , J. Virzi , O. Vitells , M. Viti , I. Vivarelli , F. Vives Vaque , S. Vlachos , D. Vladoiu ,M. Vlasak , A. Vogel , P. Vokac , G. Volpi , M. Volpi , G. Volpini , H. von der Schmitt ,H. von Radziewski , E. von Toerne , V. Vorobel , V. Vorwerk , M. Vos , R. Voss , T.T. Voss ,J.H. Vossebeld , N. Vranjes , M. Vranjes Milosavljevic , V. Vrba , M. Vreeswijk , T. Vu Anh ,R. Vuillermet , I. Vukotic , W. Wagner , P. Wagner , H. Wahlen , S. Wahrmund , J. Wakabayashi ,S. Walch , J. Walder , R. Walker , W. Walkowiak , R. Wall , P. Waller , B. Walsh , C. Wang ,H. Wang , H. Wang ,ak , J. Wang , J. Wang , R. Wang , S.M. Wang , T. Wang , A. Warburton ,C.P. Ward , M. Warsinsky , A. Washbrook , C. Wasicki , I. Watanabe , P.M. Watkins , A.T. Watson ,I.J. Watson , M.F. Watson , G. Watts , S. Watts , A.T. Waugh , B.M. Waugh , M.S. Weber ,P. Weber , A.R. Weidberg , P. Weigell , J. Weingarten , C. Weiser , H. Wellenstein , P.S. Wells ,T. Wenaus , D. Wendland , Z. Weng ,w , T. Wengler , S. Wenig , N. Wermes , M. Werner , P. Werner ,M. Werth , M. Wessels , J. Wetter , C. Weydert , K. Whalen , S.J. Wheeler-Ellis , A. White ,M.J. White , S. White , , S.R. Whitehead , D. Whiteson , D. Whittington , F. Wicek ,D. Wicke , F.J. Wickens , W. Wiedenmann , M. Wielers , P. Wienemann , C. Wiglesworth ,L.A.M. Wiik-Fuchs , P.A. Wijeratne , A. Wildauer , M.A. Wildt ,s , I. Wilhelm , H.G. Wilkens ,J.Z. Will , E. Williams , H.H. Williams , W. Willis , S. Willocq , J.A. Wilson , M.G. Wilson ,A. Wilson , I. Wingerter-Seez , S. Winkelmann , F. Winklmeier , M. Wittgen , S.J. Wollstadt ,M.W. Wolter , H. Wolters ,h , W.C. Wong , G. Wooden , B.K. Wosiek , J. Wotschack ,M.J. Woudstra , K.W. Wozniak , K. Wraight , M. Wright , B. Wrona , S.L. Wu , X. Wu , Y. Wu ,al ,E. Wulf , B.M. Wynne , S. Xella , M. Xiao , S. Xie , C. Xu ,z , D. Xu , B. Yabsley , S. Yacoob ,M. Yamada , H. Yamaguchi , A. Yamamoto , K. Yamamoto , S. Yamamoto , T. Yamamura ,T. Yamanaka , J. Yamaoka , T. Yamazaki , Y. Yamazaki , Z. Yan , H. Yang , U.K. Yang , Y. Yang ,Z. Yang , , S. Yanush , L. Yao , Y. Yao , Y. Yasu , G.V. Ybeles Smit , J. Ye , S. Ye ,M. Yilmaz , R. Yoosoofmiya , K. Yorita , R. Yoshida , C. Young , C.J. Young , S. Youssef , D. Yu ,J. Yu , J. Yu , L. Yuan , A. Yurkewicz , M. Byszewski , B. Zabinski , R. Zaidan , A.M. Zaitsev ,Z. Zajacova , L. Zanello , , A. Zaytsev , C. Zeitnitz , M. Zeman , A. Zemla , C. Zendler ,O. Zenin , T. ˇ Zeniˇ s , Z. Zinonos , , S. Zenz , D. Zerwas , G. Zevi della Porta , Z. Zhan , D. Zhang ,ak , H. Zhang , J. Zhang , X. Zhang , Z. Zhang , L. Zhao , T. Zhao , Z. Zhao ,A. Zhemchugov , J. Zhong , B. Zhou , N. Zhou , Y. Zhou , C.G. Zhu , H. Zhu , J. Zhu , Y. Zhu ,X. Zhuang , V. Zhuravlov , D. Zieminska , N.I. Zimin , R. Zimmermann , S. Zimmermann ,S. Zimmermann , M. Ziolkowski , R. Zitoun , L. ˇZivkovi´c , V.V. Zmouchko , ∗ , G. Zobernig ,A. Zoccoli , , M. zur Nedden , V. Zutshi , L. Zwalinski . Physics Department, SUNY Albany, Albany NY, United States of America Department of Physics, University of Alberta, Edmonton AB, Canada a ) Department of Physics, Ankara University, Ankara; ( b ) Department of Physics, Dumlupinar University,Kutahya; ( c ) Department of Physics, Gazi University, Ankara; ( d ) Division of Physics, TOBB University ofEconomics and Technology, Ankara; ( e ) Turkish Atomic Energy Authority, Ankara, Turkey LAPP, CNRS/IN2P3 and Universit´e de Savoie, Annecy-le-Vieux, France High Energy Physics Division, Argonne National Laboratory, Argonne IL, United States of America Department of Physics, University of Arizona, Tucson AZ, United States of America Department of Physics, The University of Texas at Arlington, Arlington TX, United States of America Physics Department, University of Athens, Athens, Greece Physics Department, National Technical University of Athens, Zografou, Greece Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan Institut de F´ısica d’Altes Energies and Departament de F´ısica de la Universitat Aut`onoma de Barcelona andICREA, Barcelona, Spain
12 ( a ) Institute of Physics, University of Belgrade, Belgrade; ( b ) Vinca Institute of Nuclear Sciences, University ofBelgrade, Belgrade, Serbia Department for Physics and Technology, University of Bergen, Bergen, Norway Physics Division, Lawrence Berkeley National Laboratory and University of California, Berkeley CA, UnitedStates of America Department of Physics, Humboldt University, Berlin, Germany Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern,Bern, Switzerland School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
18 ( a ) Department of Physics, Bogazici University, Istanbul; ( b ) Division of Physics, Dogus University, Istanbul; ( c ) Department of Physics Engineering, Gaziantep University, Gaziantep; ( d ) Department of Physics, IstanbulTechnical University, Istanbul, Turkey
19 ( a ) INFN Sezione di Bologna; ( b ) Dipartimento di Fisica, Universit`a di Bologna, Bologna, Italy Physikalisches Institut, University of Bonn, Bonn, Germany Department of Physics, Boston University, Boston MA, United States of America Department of Physics, Brandeis University, Waltham MA, United States of America
23 ( a ) Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro; ( b ) Federal University of Juiz deFora (UFJF), Juiz de Fora; ( c ) Federal University of Sao Joao del Rei (UFSJ), Sao Joao del Rei; ( d ) Instituto deFisica, Universidade de Sao Paulo, Sao Paulo, Brazil Physics Department, Brookhaven National Laboratory, Upton NY, United States of America
25 ( a ) National Institute of Physics and Nuclear Engineering, Bucharest; ( b ) University Politehnica Bucharest,Bucharest; ( c ) West University in Timisoara, Timisoara, Romania Departamento de F´ısica, Universidad de Buenos Aires, Buenos Aires, Argentina Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom Department of Physics, Carleton University, Ottawa ON, Canada CERN, Geneva, Switzerland Enrico Fermi Institute, University of Chicago, Chicago IL, United States of America
31 ( a ) Departamento de F´ısica, Pontificia Universidad Cat´olica de Chile, Santiago; ( b ) Departamento de F´ısica,Universidad T´ecnica Federico Santa Mar´ıa, Valpara´ıso, Chile
32 ( a ) Institute of High Energy Physics, Chinese Academy of Sciences, Beijing; ( b ) Department of ModernPhysics, University of Science and Technology of China, Anhui; ( c ) Department of Physics, Nanjing University,Jiangsu; ( d ) School of Physics, Shandong University, Shandong, China Laboratoire de Physique Corpusculaire, Clermont Universit´e and Universit´e Blaise Pascal and CNRS/IN2P3,Aubiere Cedex, France Nevis Laboratory, Columbia University, Irvington NY, United States of America Niels Bohr Institute, University of Copenhagen, Kobenhavn, Denmark
36 ( a ) INFN Gruppo Collegato di Cosenza; ( b ) Dipartimento di Fisica, Universit`a della Calabria, Arcavata diRende, Italy AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow,Poland The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland Physics Department, Southern Methodist University, Dallas TX, United States of America Physics Department, University of Texas at Dallas, Richardson TX, United States of America DESY, Hamburg and Zeuthen, Germany Institut f¨ur Experimentelle Physik IV, Technische Universit¨at Dortmund, Dortmund, Germany Institut f¨ur Kern- und Teilchenphysik, Technical University Dresden, Dresden, Germany Department of Physics, Duke University, Durham NC, United States of America SUPA - School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom INFN Laboratori Nazionali di Frascati, Frascati, Italy Fakult¨at f¨ur Mathematik und Physik, Albert-Ludwigs-Universit¨at, Freiburg, Germany Section de Physique, Universit´e de Gen`eve, Geneva, Switzerland
49 ( a ) INFN Sezione di Genova; ( b ) Dipartimento di Fisica, Universit`a di Genova, Genova, Italy
50 ( a ) E. Andronikashvili Institute of Physics, Tbilisi State University, Tbilisi; ( b ) High Energy Physics Institute,Tbilisi State University, Tbilisi, Georgia II Physikalisches Institut, Justus-Liebig-Universit¨at Giessen, Giessen, Germany SUPA - School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom II Physikalisches Institut, Georg-August-Universit¨at, G¨ottingen, Germany Laboratoire de Physique Subatomique et de Cosmologie, Universit´e Joseph Fourier and CNRS/IN2P3 andInstitut National Polytechnique de Grenoble, Grenoble, France Department of Physics, Hampton University, Hampton VA, United States of America Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge MA, United States of America
57 ( a ) Kirchhoff-Institut f¨ur Physik, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg; ( b ) PhysikalischesInstitut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg; ( c ) ZITI Institut f¨ur technische Informatik,Ruprecht-Karls-Universit¨at Heidelberg, Mannheim, Germany Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan Department of Physics, Indiana University, Bloomington IN, United States of America Institut f¨ur Astro- und Teilchenphysik, Leopold-Franzens-Universit¨at, Innsbruck, Austria University of Iowa, Iowa City IA, United States of America Department of Physics and Astronomy, Iowa State University, Ames IA, United States of America Joint Institute for Nuclear Research, JINR Dubna, Dubna, Russia KEK, High Energy Accelerator Research Organization, Tsukuba, Japan Graduate School of Science, Kobe University, Kobe, Japan Faculty of Science, Kyoto University, Kyoto, Japan Kyoto University of Education, Kyoto, Japan Department of Physics, Kyushu University, Fukuoka, Japan Instituto de F´ısica La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina Physics Department, Lancaster University, Lancaster, United Kingdom
71 ( a ) INFN Sezione di Lecce; ( b ) Dipartimento di Matematica e Fisica, Universit`a del Salento, Lecce, Italy Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom Department of Physics, Joˇzef Stefan Institute and University of Ljubljana, Ljubljana, Slovenia School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom Department of Physics, Royal Holloway University of London, Surrey, United Kingdom Department of Physics and Astronomy, University College London, London, United Kingdom Laboratoire de Physique Nucl´eaire et de Hautes Energies, UPMC and Universit´e Paris-Diderot andCNRS/IN2P3, Paris, France Fysiska institutionen, Lunds universitet, Lund, Sweden Departamento de Fisica Teorica C-15, Universidad Autonoma de Madrid, Madrid, Spain Institut f¨ur Physik, Universit¨at Mainz, Mainz, Germany School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom CPPM, Aix-Marseille Universit´e and CNRS/IN2P3, Marseille, France Department of Physics, University of Massachusetts, Amherst MA, United States of America Department of Physics, McGill University, Montreal QC, Canada School of Physics, University of Melbourne, Victoria, Australia Department of Physics, The University of Michigan, Ann Arbor MI, United States of America Department of Physics and Astronomy, Michigan State University, East Lansing MI, United States of America
88 ( a ) INFN Sezione di Milano; ( b ) Dipartimento di Fisica, Universit`a di Milano, Milano, Italy B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Republic of Belarus National Scientific and Educational Centre for Particle and High Energy Physics, Minsk, Republic of Belarus Department of Physics, Massachusetts Institute of Technology, Cambridge MA, United States of America Group of Particle Physics, University of Montreal, Montreal QC, Canada P.N. Lebedev Institute of Physics, Academy of Sciences, Moscow, Russia Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia Moscow Engineering and Physics Institute (MEPhI), Moscow, Russia Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia Fakult¨at f¨ur Physik, Ludwig-Maximilians-Universit¨at M¨unchen, M¨unchen, Germany Max-Planck-Institut f¨ur Physik (Werner-Heisenberg-Institut), M¨unchen, Germany Nagasaki Institute of Applied Science, Nagasaki, Japan
Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan
101 ( a ) INFN Sezione di Napoli; ( b ) Dipartimento di Scienze Fisiche, Universit`a di Napoli, Napoli, Italy
Department of Physics and Astronomy, University of New Mexico, Albuquerque NM, United States ofAmerica
Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef,Nijmegen, Netherlands
Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands
Department of Physics, Northern Illinois University, DeKalb IL, United States of America
Budker Institute of Nuclear Physics, SB RAS, Novosibirsk, Russia
Department of Physics, New York University, New York NY, United States of America
Ohio State University, Columbus OH, United States of America
Faculty of Science, Okayama University, Okayama, Japan
Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman OK, UnitedStates of America
Department of Physics, Oklahoma State University, Stillwater OK, United States of America
Palack´y University, RCPTM, Olomouc, Czech Republic
Center for High Energy Physics, University of Oregon, Eugene OR, United States of America
LAL, Universit´e Paris-Sud and CNRS/IN2P3, Orsay, France
Graduate School of Science, Osaka University, Osaka, Japan
Department of Physics, University of Oslo, Oslo, Norway
Department of Physics, Oxford University, Oxford, United Kingdom
118 ( a ) INFN Sezione di Pavia; ( b ) Dipartimento di Fisica, Universit`a di Pavia, Pavia, Italy
Department of Physics, University of Pennsylvania, Philadelphia PA, United States of America
Petersburg Nuclear Physics Institute, Gatchina, Russia
121 ( a ) INFN Sezione di Pisa; ( b ) Dipartimento di Fisica E. Fermi, Universit`a di Pisa, Pisa, Italy
Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh PA, United States of America
123 ( a ) Laboratorio de Instrumentacao e Fisica Experimental de Particulas - LIP, Lisboa, Portugal; ( b ) Departamento de Fisica Teorica y del Cosmos and CAFPE, Universidad de Granada, Granada, Spain
Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic
Faculty of Mathematics and Physics, Charles University in Prague, Praha, Czech Republic
Czech Technical University in Prague, Praha, Czech Republic State Research Center Institute for High Energy Physics, Protvino, Russia
Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom
Physics Department, University of Regina, Regina SK, Canada
Ritsumeikan University, Kusatsu, Shiga, Japan
131 ( a ) INFN Sezione di Roma I; ( b ) Dipartimento di Fisica, Universit`a La Sapienza, Roma, Italy
132 ( a ) INFN Sezione di Roma Tor Vergata; ( b ) Dipartimento di Fisica, Universit`a di Roma Tor Vergata, Roma,Italy
133 ( a ) INFN Sezione di Roma Tre; ( b ) Dipartimento di Fisica, Universit`a Roma Tre, Roma, Italy
134 ( a ) Facult´e des Sciences Ain Chock, R´eseau Universitaire de Physique des Hautes Energies - Universit´eHassan II, Casablanca; ( b ) Centre National de l’Energie des Sciences Techniques Nucleaires, Rabat; ( c ) Facult´edes Sciences Semlalia, Universit´e Cadi Ayyad, LPHEA-Marrakech; ( d ) Facult´e des Sciences, Universit´e MohamedPremier and LPTPM, Oujda; ( e ) Facult´e des sciences, Universit´e Mohammed V-Agdal, Rabat, Morocco
DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de l’Univers), CEA Saclay (Commissariat al’Energie Atomique), Gif-sur-Yvette, France
Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz CA, United Statesof America
Department of Physics, University of Washington, Seattle WA, United States of America
Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom
Department of Physics, Shinshu University, Nagano, Japan
Fachbereich Physik, Universit¨at Siegen, Siegen, Germany
Department of Physics, Simon Fraser University, Burnaby BC, Canada
SLAC National Accelerator Laboratory, Stanford CA, United States of America
143 ( a ) Faculty of Mathematics, Physics & Informatics, Comenius University, Bratislava; ( b ) Department ofSubnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, SlovakRepublic
144 ( a ) Department of Physics, University of Johannesburg, Johannesburg; ( b ) School of Physics, University of theWitwatersrand, Johannesburg, South Africa
145 ( a ) Department of Physics, Stockholm University; ( b ) The Oskar Klein Centre, Stockholm, Sweden
Physics Department, Royal Institute of Technology, Stockholm, Sweden
Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook NY, UnitedStates of America
Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom
School of Physics, University of Sydney, Sydney, Australia
Institute of Physics, Academia Sinica, Taipei, Taiwan
Department of Physics, Technion: Israel Institute of Technology, Haifa, Israel
Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel
Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
International Center for Elementary Particle Physics and Department of Physics, The University of Tokyo,Tokyo, Japan
Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan
Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
Department of Physics, University of Toronto, Toronto ON, Canada
158 ( a ) TRIUMF, Vancouver BC; ( b ) Department of Physics and Astronomy, York University, Toronto ON,Canada
Institute of Pure and Applied Sciences, University of Tsukuba,1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571,Japan
Science and Technology Center, Tufts University, Medford MA, United States of America
Centro de Investigaciones, Universidad Antonio Narino, Bogota, Colombia
Department of Physics and Astronomy, University of California Irvine, Irvine CA, United States of America
163 ( a ) INFN Gruppo Collegato di Udine; ( b ) ICTP, Trieste; ( c ) Dipartimento di Chimica, Fisica e Ambiente,Universit`a di Udine, Udine, Italy
Department of Physics, University of Illinois, Urbana IL, United States of America
Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden Instituto de F´ısica Corpuscular (IFIC) and Departamento de F´ısica At´omica, Molecular y Nuclear andDepartamento de Ingenier´ıa Electr´onica and Instituto de Microelectr´onica de Barcelona (IMB-CNM), Universityof Valencia and CSIC, Valencia, Spain
Department of Physics, University of British Columbia, Vancouver BC, Canada
Department of Physics and Astronomy, University of Victoria, Victoria BC, Canada
Department of Physics, University of Warwick, Coventry, United Kingdom
Waseda University, Tokyo, Japan
Department of Particle Physics, The Weizmann Institute of Science, Rehovot, Israel
Department of Physics, University of Wisconsin, Madison WI, United States of America
Fakult¨at f¨ur Physik und Astronomie, Julius-Maximilians-Universit¨at, W¨urzburg, Germany
Fachbereich C Physik, Bergische Universit¨at Wuppertal, Wuppertal, Germany
Department of Physics, Yale University, New Haven CT, United States of America
Yerevan Physics Institute, Yerevan, Armenia
Domaine scientifique de la Doua, Centre de Calcul CNRS/IN2P3, Villeurbanne Cedex, France a Also at Laboratorio de Instrumentacao e Fisica Experimental de Particulas - LIP, Lisboa, Portugal b Also at Faculdade de Ciencias and CFNUL, Universidade de Lisboa, Lisboa, Portugal c Also at Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom d Also at TRIUMF, Vancouver BC, Canada e Also at Department of Physics, California State University, Fresno CA, United States of America f Also at Novosibirsk State University, Novosibirsk, Russia g Also at Fermilab, Batavia IL, United States of America h Also at Department of Physics, University of Coimbra, Coimbra, Portugal i Also at Department of Physics, UASLP, San Luis Potosi, Mexico j Also at Universit`a di Napoli Parthenope, Napoli, Italy k Also at Institute of Particle Physics (IPP), Canada l Also at Department of Physics, Middle East Technical University, Ankara, Turkey m Also at Louisiana Tech University, Ruston LA, United States of America n Also at Dep Fisica and CEFITEC of Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa,Caparica, Portugal o Also at Department of Physics and Astronomy, University College London, London, United Kingdom p Also at Group of Particle Physics, University of Montreal, Montreal QC, Canada q Also at Department of Physics, University of Cape Town, Cape Town, South Africa r Also at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan s Also at Institut f¨ur Experimentalphysik, Universit¨at Hamburg, Hamburg, Germany t Also at Manhattan College, New York NY, United States of America u Also at School of Physics, Shandong University, Shandong, China v Also at CPPM, Aix-Marseille Universit´e and CNRS/IN2P3, Marseille, France w Also at School of Physics and Engineering, Sun Yat-sen University, Guangzhou, China x Also at Academia Sinica Grid Computing, Institute of Physics, Academia Sinica, Taipei, Taiwan y Also at Dipartimento di Fisica, Universit`a La Sapienza, Roma, Italy z Also at DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de l’Univers), CEA Saclay(Commissariat a l’Energie Atomique), Gif-sur-Yvette, France aa Also at Section de Physique, Universit´e de Gen`eve, Geneva, Switzerland ab Also at Departamento de Fisica, Universidade de Minho, Braga, Portugal ac Also at Department of Physics and Astronomy, University of South Carolina, Columbia SC, United States ofAmerica ad Also at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary ae Also at California Institute of Technology, Pasadena CA, United States of America af Also at Institute of Physics, Jagiellonian University, Krakow, Poland ag Also at LAL, Universit´e Paris-Sud and CNRS/IN2P3, Orsay, France ah Also at Nevis Laboratory, Columbia University, Irvington NY, United States of America ai Also at Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom aj Also at Department of Physics, Oxford University, Oxford, United Kingdom ak Also at Institute of Physics, Academia Sinica, Taipei, Taiwan al Also at Department of Physics, The University of Michigan, Ann Arbor MI, United States of America ∗∗