Measurements of differential and double-differential Drell-Yan cross sections in proton-proton collisions at 8 TeV
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP/2013-0372015/04/21
CMS-SMP-14-003
Measurements of differential and double-differentialDrell–Yan cross sections in proton-proton collisions at √ s = The CMS Collaboration ∗ Abstract
Measurements of the differential and double-differential Drell–Yan cross sections inthe dielectron and dimuon channels are presented. They are based on proton-protoncollision data at √ s = − . The measured inclusive crosssection in the Z peak region (60–120 GeV), obtained from the combination of the di-electron and dimuon channels, is 1138 ± ±
25 (theo) ±
30 (lumi) pb, where thestatistical uncertainty is negligible. The differential cross section d σ /d m in the dilep-ton mass range 15 to 2000 GeV is measured and corrected to the full phase space. Thedouble-differential cross section d σ /d m d | y | is also measured over the mass range 20to 1500 GeV and absolute dilepton rapidity from 0 to 2.4. In addition, the ratios of thenormalized differential cross sections measured at √ s = FEWZ
Published in the European Physical Journal C as doi:10.1140/epjc/s10052-015-3364-2. c (cid:13) ∗ See Appendix A for the list of collaboration members a r X i v : . [ h e p - e x ] A p r At hadron colliders, Drell–Yan (DY) lepton pairs are produced via γ ∗ /Z exchange in the s chan-nel. Theoretical calculations of the differential cross section d σ /d m and the double-differentialcross section d σ /d m d | y | , where m is the dilepton invariant mass and | y | is the absolute valueof the dilepton rapidity, are well established in the standard model (SM) up to the next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics (QCD) [1–4]. The rapiditydistributions of the gauge bosons γ ∗ /Z are sensitive to the parton content of the proton.The rapidity and the invariant mass of the dilepton system produced in proton-proton colli-sions are related at leading order to the longitudinal momentum fractions x + and x − carriedby the two interacting partons according to the formula x ± = ( m / √ s ) e ± y . Hence, the rapidityand mass distributions are sensitive to the parton distribution functions (PDFs) of the interact-ing partons. The differential cross sections are measured with respect to | y | since the rapiditydistribution is symmetric about zero. The high center-of-mass energy at the CERN LHC per-mits the study of DY production in regions of the Bjorken scaling variable and evolution scale Q = x + x − s that were not accessible in previous experiments [5–10]. The present analysis cov-ers the ranges 0.0003 < x ± < < Q <
750 000 GeV in the double-differential crosssection measurement. The differential cross section d σ /d m is measured in an even wider range300 < Q < .The increase in the center-of-mass energy at the LHC from 7 to 8 TeV provides an opportunityto measure the ratios and double-differential ratios of cross sections of various hard processes,including the DY process. Measurements of the DY process in proton-proton collisions de-pend on various theoretical parameters such as the QCD running coupling constant, PDFs,and renormalization and factorization scales. The theoretical systematic uncertainties in thecross section measurements for a given process at different center-of-mass energies are sub-stantial but correlated, so that the ratios of differential cross sections normalized to the Z bosonproduction cross section (double ratios) can be measured very precisely [11].This paper presents measurements of the DY differential cross section d σ /d m in the mass range15 < m < σ /d m d | y | in the mass range 20 < m < √ s = − . Integrated luminosities of 4.8 fb − (dielectron) and 4.5 fb − (dimuon) at √ s = x region(0.001 < x < σ /d m isimportant for various LHC physics analyses. DY events pose a major source of background forprocesses such as top quark pair production, diboson production, and Higgs measurements with lepton final states, as well as for searches for new physics beyond the SM, such as theproduction of high-mass dilepton resonances.The differential cross sections are first measured separately for both lepton flavors and found toagree. The combined cross section measurement is then compared to the NNLO QCD predic-tions computed with FEWZ σ /d m d | y | measurementis compared to the NNLO theoretical predictions computed with FEWZ
The central feature of the CMS detector is a superconducting solenoid of 6 m internal diame-ter and 13 m length, providing a magnetic field of 3.8 T. Within the field volume are a silicontracker, a crystal electromagnetic calorimeter (ECAL), and a brass/scintillator hadron calori-meter (HCAL). The tracker is composed of a pixel detector and a silicon strip tracker, whichare used to measure charged-particle trajectories and cover the full azimuthal angle and thepseudorapidity interval | η | < | η | < | η | < < | η | <
3) regions.The CMS experiment uses a two-level trigger system. The level-1 trigger, composed of customprocessing hardware, selects events of interest at an output rate of 100 kHz using informationfrom the calorimeters and muon detectors [25]. The high-level trigger (HLT) is software basedand further decreases the event collection rate to a few hundred hertz by using the full eventinformation, including that from the tracker [26]. A more detailed description of the CMSdetector, together with a definition of the coordinate system used and the relevant kinematicvariables, can be found in [27].
Several simulated samples are used for determining efficiencies, acceptances, and backgroundsfrom processes that result in two leptons, and for the determination of systematic uncertainties.The DY signal samples with e + e − and µ + µ − final states are generated with the next-to-leading(NLO) generator POWHEG [28–31] interfaced with the
PYTHIA v6.4.24 [32] parton shower gen-erator.
PYTHIA is used to model QED final-state radiation (FSR).The
POWHEG simulated sample is based on NLO calculations, and a correction is appliedto take into account higher-order QCD and electroweak (EW) effects. The correction factorsbinned in dilepton rapidity y and transverse momentum p T are determined in each invariant-mass bin to be the ratio of the double-differential cross sections calculated at NNLO QCD andNLO EW with FEWZ
POWHEG , as described in [12]. The correspondinghigher-order effects depend on the dilepton kinematic variables. Higher-order EW correctionsare small in comparison to FSR corrections. They increase for invariant masses in the TeVregion [33], but are insignificant compared to the experimental precision for the whole massrange under study. The NNLO QCD effects are most important in the low-mass region. The ef- fect of the correction factors on the acceptance ranges up to 50% in the low-mass region (below40 GeV), but is almost negligible in the high-mass region (above 200 GeV).The main SM background processes are simulated with
POWHEG (DY → τ + τ − , single topquark) and with M AD G RAPH [34] (tt, diboson events WW/WZ/ZZ). Both
POWHEG and M AD -G RAPH are interfaced with the
TAUOLA package [35], which handles decays of τ leptons. Thenormalization of the tt sample is set to the NNLO cross section of 245.8 pb [36]. Multijet QCDbackground events are produced with PYTHIA .All generated events are processed through a detailed simulation of the CMS detector based onG
EANT
The events used in the analysis are selected with a dielectron or a dimuon trigger. Dielectronevents are triggered by the presence of two electron candidates that pass loose requirementson the electron quality and isolation with a minimum transverse momentum p T of 17 GeV forone of the electrons and 8 GeV for the other. The dimuon trigger requires one muon with p T >
17 GeV and a second muon with p T > χ probability from a kinematic fit to the dimuon vertex is selected.Electron and muon isolation criteria are based on measuring the sum of energy depositions as-sociated with photons and charged and neutral hadrons reconstructed and identified by meansof the CMS particle-flow algorithm [44–47]. Isolation sums are evaluated in a circular regionof the ( η , φ ) plane around the lepton candidate with ∆ R < ∆ R = √ ( ∆ η ) + ( ∆ φ ) ), and are corrected for the contribution from pileup.Each lepton is required to be within the geometrical acceptance of | η | < p T >
20 GeV and the trailing lepton p T >
10 GeV, whichcorresponds to the plateau of the trigger efficiency. Both lepton candidates in each event usedin the offline analysis are required to match HLT trigger objects.After event selection, the analysis follows a series of steps. First, backgrounds are estimated.Next, the observed background-subtracted yield is unfolded to correct for the effects of themigration of events among bins of mass and rapidity due to the detector resolution. The accep-tance and efficiency corrections are then applied. Finally, the migration of events due to FSR iscorrected. Systematic uncertainties associated with each of the analysis steps are evaluated.
The major background contributions in the dielectron channel arise from τ + τ − and tt processesin the low-mass region and from QCD events with multiple jets at high invariant mass. Thebackground composition is somewhat different in the dimuon final state. Multijet events andDY production of τ + τ − pairs are the dominant sources of background in the dimuon chan-nel at low invariant mass and in the region just below the Z peak. Diboson and tt productionfollowed by leptonic decays are the dominant sources of background at high invariant mass.Lepton pair production in γγ -initiated processes, where both initial-state protons radiate aphoton, is significant at high mass. The contribution from this channel is treated as an irre-ducible background and is estimated with FEWZ τ + τ − , and WW. Notably, these final statescontain electron-muon pairs at twice the rate of electron or muon pairs. These electron-muonpairs can be cleanly identified from a data sample of e µ events and properly scaled (taking intoaccount the detector acceptance and efficiency) in order to calculate the background contribu- E n t r i e s pe r b i n data ee → */Z γ ττ→ */Z γ EW Wt+tW+t t QCD
CMS (8 TeV) -1 m(ee) [GeV] D a t a / M C E n t r i e s pe r b i n data µµ→ */Z γ ττ→ */Z γ EW Wt+tW+t t QCD
CMS (8 TeV) -1 ) [GeV] µµ m( D a t a / M C Figure 1: The dielectron (left) and dimuon (right) invariant-mass spectra observed in dataand predicted by Monte Carlo (MC) simulation and the corresponding ratios of observed toexpected yields. The QCD multijet contributions in both decay channels are predicted usingcontrol samples in data. The EW histogram indicates the diboson and W+jets production. Thesimulated signal distributions are based on the NNLO-reweighted
POWHEG sample. No othercorrections are applied. Error bars are statistical only.tion to the dielectron and dimuon channels.Background yields estimated from an e µ data sample are used to reduce the systematic uncer-tainty due to the limited theoretical knowledge of the cross sections of the SM processes. Theresidual differences between background contributions estimated from data and simulation aretaken into account in the systematic uncertainty assignment, as detailed in Section 9.The dilepton yields for data and simulated events in bins of invariant mass are reported inFig. 1. The photon-induced background is absorbed in the signal distribution so no correctionis applied at this stage. As shown in the figure, the background contribution at low mass is nolarger than 5% in both decay channels. In the high-mass region, background contamination ismore significant, reaching approximately 50% (30%) in the dielectron (dimuon) distribution. Imperfect lepton energy and momentum measurements can affect the reconstructed dileptoninvariant-mass distributions. Correcting for these effects is important in precise measurementsof differential cross sections.A momentum scale correction to remove a bias in the reconstructed muon momenta due to thedifferences in the tracker misalignment between data and simulation and the residual magneticfield mismodeling is applied following the standard CMS procedure described in [50].The electron energy deposits as measured in the ECAL are subject to a set of corrections involv-ing information both from the ECAL and the tracker, following the standard CMS proceduresfor the 8 TeV data set [51]. A final electron energy scale correction, which goes beyond thestandard set of corrections, is derived from an analysis of the Z → e + e − peak according to m(ee) (post-FSR) [GeV] F r a c t i on o f e v en t s -3 -2 -1
101 20 50 100 200 500 1000 2000 A ˛ ˛ · A ee fi */Z g CMS
Simulation ) (post-FSR) [GeV] mm m( F r a c t i on o f e v en t s -3 -2 -1
101 20 50 100 200 500 1000 2000 A ˛ ˛ · A mm fi */Z g CMS
Simulation
Figure 2: The DY acceptance, efficiency, and their product per invariant-mass bin in the dielec-tron channel (left) and the dimuon channel (right), where “post-FSR” means dilepton invariantmass after the simulation of FSR.the procedure described in [49], and consists of a simple factor of 1.001 applied to the electronenergies to account for the different selection used in this analysis.The detector resolution effects that cause a migration of events among the analysis bins arecorrected through an iterative unfolding procedure [52]. This procedure maps the measuredlepton distribution onto the true one, while taking into account the migration of events in andout of the mass and rapidity range of this measurement.The effects of the unfolding correction in the differential cross section measurement are approx-imately 50 (20)% for dielectron (dimuon) channel in the Z peak region, where the invariant-mass spectrum changes steeply. Less significant effects, of the order of 15% (5%) in dielectron(dimuon) channel, are observed in other regions. The effect on the double-differential crosssection measurement is less significant as both the invariant mass and rapidity bins are signifi-cantly wider than the respective detector resolutions. The effect for dielectrons reaches 15% inthe 45–60 GeV mass region and 5% at high mass; it is, however, less than 1% for dimuons overthe entire invariant mass-rapidity range of study.
The acceptance A is defined as the fraction of simulated signal events with both leptons pass-ing the nominal p T and η requirements of the analysis. It is determined using the NNLOreweighted POWHEG simulated sample, after the simulation of FSR.The efficiency (cid:101) is the fraction of events in the DY simulated sample that are inside the accep-tance and pass the full selection. The following equation holds: A (cid:101) ≡ N A N gen N (cid:101) N A = N (cid:101) N gen , (1)where N gen is the number of generated signal events in a given invariant-mass bin, N A is thenumber of events inside the geometrical and kinematic acceptances, and N (cid:101) is the number ofevents passing the event selection criteria. Figure 2 shows the acceptance, the efficiency, andtheir product as functions of the dilepton invariant mass.The DY acceptance is obtained from simulation. In the lowest mass bin it is only about 0.5%,rapidly increasing to 50% in the Z peak region and reaching over 90% at high mass. The efficiency is factorized into the reconstruction, identification, and isolation efficiencies andthe event trigger efficiency. The factorization procedure takes into account the asymmetric p T selections for the two legs of the dielectron trigger. The efficiency is obtained from simu-lation, rescaled with a correction factor that takes into account differences between data andsimulation. The efficiency correction factor is determined in bins of lepton p T and η usingZ → e + e − ( µ + µ − ) events in data and simulation with the tag-and-probe method [49] and isthen applied as a weight to simulated events on a per-lepton basis.A typical dimuon event efficiency is 70–80% throughout the entire mass range. In the dielec-tron channel, the efficiency at low mass is only 20–40% because of tighter lepton identificationrequirements, and reaches 65% at high mass. The trigger efficiency for events within the geo-metrical acceptance is greater than 98% (93%) for the dielectron (dimuon) signal. The efficiencyis significantly affected by the pileup in the event. The effect on the isolation efficiency is up to5% (about 1%) in the dielectron (dimuon) channel.A dip in the event efficiency in the mass range 30–40 GeV, visible in Fig. 2, is caused by the com-bination of two factors. On one hand, the lepton reconstruction and identification efficienciesdecrease as the lepton p T decreases. On the other hand, the kinematic acceptance requirementspreferentially select DY events produced beyond the leading order, which results in higher p T leptons with higher reconstruction and identification efficiencies, in the mass range below 30–40 GeV. The effect is more pronounced for dielectrons than for dimuons because the electronreconstruction and identification efficiencies depend more strongly on p T .For the dimuon channel the efficiency correction factor is 0.95–1.10, rising up to 1.10 at highdimuon rapidity and falling to 0.95 at low mass. At low mass, the correction to the muon re-construction and identification efficiency is dominant, falling to 0.94. In the dielectron channel,the efficiency correction factor is 0.96–1.05 in the Z peak region, and 0.90 at low mass. Thecorrection factor rises to 1.05 at high dielectron rapidity. The correction to the electron identifi-cation and isolation efficiency is dominant in the dielectron channel, reaching 0.93 at low massand 1.04 at high rapidity. The effect of photon radiation from the final-state leptons (FSR effect) moves the measured in-variant mass of the dilepton pair to lower values, significantly affecting the mass spectrum,particularly in the region below the Z peak. A correction for FSR is performed to facilitate thecomparison to the theoretical predictions and to properly combine the measurements in thedielectron and dimuon channels. The FSR correction is estimated separately from the detectorresolution correction by means of the same unfolding technique. An additional bin-by-bin cor-rection is applied for the events in which the leptons generated before FSR modeling (pre-FSR)fail the acceptance requirements, while they pass after the FSR modeling (post-FSR), follow-ing the approach described in [12]. The correction for the events not included in the responsematrix is significant at low mass, reaching a maximum of 20% in the lowest mass bin and de-creasing to negligible levels in the Z peak region.The magnitude of the FSR correction below the Z peak is on the order of 40–60% (30–50%)for the dielectron (dimuon) channel. In other mass regions, the effect is only 10–15% in bothchannels. In the double-differential cross section measurement, the effect of FSR unfolding isnot significant, typically a few percent, due to a larger mass bin size.In order to compare the measurements corrected for FSR obtained in analyses with various event generators, the “dressed” lepton quantities can be considered. The dressed lepton four-momentum is defined as p dressed (cid:96) = p post-FSR (cid:96) + ∑ p γ , (2)where all the simulated photons originating from leptons are summed within a cone of ∆ R < Acceptance uncertainty.
The dominant uncertainty sources pertaining to the acceptance are(1) the theoretical uncertainty from imperfect knowledge of the nonperturbative PDFs con-tributing to the hard scattering and (2) the modeling uncertainty. The latter comes from theprocedure to apply weights to the NLO simulated sample in order to reproduce NNLO kine-matics and affects mostly the acceptance calculations at very low invariant mass. The PDFuncertainties for the differential and double-differential cross section measurements are calcu-lated using the LHAGLUE interface to the PDF library LHAPDF 5.8.7 [53, 54] by applying areweighting technique with asymmetric uncertainties as described in [55]. These contributionsare largest at low and high masses (4–5%) and decrease to less than 1% for masses at the Zpeak.
Efficiency uncertainty.
The systematic uncertainty in the efficiency estimation consists of twocomponents: the uncertainty in the efficiency correction factor estimation and the uncertaintyrelated to the number of simulated events. The efficiency correction factor reflects systematicdeviations between data and simulation. It varies up to 10% (7%) for the dielectron (dimuon)channel. As discussed in Section 7, single-lepton efficiencies of several types are measuredwith the tag-and-probe procedure and are combined into efficiency correction factors. The tag-and-probe procedure provides the efficiencies for each lepton type and the associated statisticaluncertainties. A variety of possible systematic biases in the tag-and-probe procedure have beentaken into account, such as dependence on the binning in single-lepton p T and η , dependenceon the assumed shape of signal and background in the fit model, and the effect of pileup. Inthe dielectron channel, this uncertainty is as large as 3.2% at low mass, and 6% at high rapidityin the 200–1500 GeV region. The uncertainty in the dimuon channel is about 1% in most ofthe analysis bins, reaching up to 4% at high rapidity in the 200–1500 GeV mass region. Thecontribution from the dimuon vertex selection is small because its efficiency correction factoris consistent with being constant. Electron energy scale.
In the dielectron channel, one of the leading systematic uncertainties isassociated with the energy scale corrections for individual electrons. The corrections affectboth the placement of a given candidate in a particular invariant-mass bin and the likelihoodof surviving the kinematic selection. The energy scale corrections are calibrated to a precision of0.1–0.2%. The systematic uncertainties in the measured cross sections are estimated by varyingthe electron energy scale by 0.2%. The uncertainty is relatively small at low masses. It reachesup to 6.2% in the Z peak region where the mass bins are the narrowest and the variation of thecross section with mass is the largest.
Muon momentum scale.
The uncertainty in the muon momentum scale causes uncertainties inthe efficiency estimation and background subtraction and affects the detector resolution un-folding. The muon momentum scale is calibrated to 0.02% precision. The systematic uncer- tainty in the measured cross sections is determined by varying the muon momentum scalewithin its uncertainty. The largest effect on the final results is observed in the detector resolu-tion unfolding step, reaching 2%.
Detector resolution.
For both channels, the simulation of the CMS detector, used for detector res-olution unfolding, provides a reliable description of the data. Possible small systematic errorsin the unfolding are related to effects such as differences in the electron energy scale and muonmomentum scale and uncertainties in FSR simulation and in simulated pileup. The impact ofeach of these effects on the measurements is studied separately, as described in this section.The detector resolution unfolding procedure itself has been thoroughly validated, includinga variety of closure tests and comparisons between different event generators; the systematicuncertainty assigned to the unfolding procedure is based on the finite size of the simulatedsamples and a contribution due to the systematic difference in data and simulation. The lattermust be taken into account because the response matrix is determined from simulation.
Background uncertainty.
The background estimation uncertainties are evaluated in the same wayin both the dielectron and dimuon channels. The uncertainty in the background is comprisedof the Poissonian statistical uncertainty of predicted backgrounds and the difference betweenthe predictions from the data and simulation. The two components are combined in quadra-ture. The uncertainty in the background is no larger than 3.0% (1.0%) at low mass, reaching16.3% (4.6%) in the highest mass bin in the dielectron (dimuon) channel. γγ -initiated background uncertainty. The uncertainty in the correction for γγ -initiated processesis estimated using FEWZ
FSR simulation.
The systematic uncertainty due to the model-dependent FSR simulation isestimated using two reweighting techniques described in [12] with the same procedure inboth decay channels. The systematic uncertainty from modeling the FSR effects is as largeas 2.5% (1.1%) in the dielectron (dimuon) channel in the 45–60 GeV region. The systematic un-certainties related to the FSR simulation in the electron channel primarily affect the detectorresolution unfolding procedure. The impact of these uncertainties is greater for the electronchannel than for the muon channel because of the partial recovery of FSR photons during theclustering of electron energy in the ECAL. The effect of the FSR simulation on other analysissteps for the electron channel is negligible in comparison to other systematic effects associatedwith those steps.
Luminosity uncertainty.
The uncertainty in the integrated luminosity recorded by CMS in the2012 data set is 2.6% [56].Table 1 summarizes the systematic uncertainties for the dielectron and dimuon channels.
Systematic uncertainties in the double ratio.
In the double ratio measurements most of the theoret-ical uncertainties are reduced. The PDF and modeling uncertainties in the acceptance and thesystematic uncertainty in the FSR modeling are fully correlated between 7 and 8 TeV measure-ments. The relative uncertainty δσ s i / σ s i in the cross section ratio corresponding to a correlatedsystematic source of uncertainty s i is estimated according to δσ s i σ s i = + δ s i ( ) + δ s i ( ) −
1, (3)where the δ s i are relative uncertainties caused by a source s i in the cross section measurementsat √ s =
10 Results and discussion
Table 1: Typical systematic uncertainties (in percent) at low mass (below 40 GeV), in the Z peakregion (60 < m <
120 GeV), and at high mass (above 200 GeV) for the dielectron and dimuonchannels; “—” means that the source does not apply.Sources e + e − µ + µ − Efficiency 2.9, 0.5, 0.7 1.0, 0.4, 1.8Detector resolution 1.2, 5.4, 1.8 0.6, 1.8, 1.6Background estimation 2.2, 0.1, 13.8 1.0, 0.1, 4.6Electron energy scale 0.2, 2.4, 2.0 —Muon momentum scale — 0.2, 1.7, 1.6FSR simulation 0.4, 0.3, 0.3 0.4, 0.2, 0.5Total experimental 3.7, 2.5, 14.0 1.6, 2.5, 5.4Theoretical uncertainty 4.2, 1.6, 5.3 4.1, 1.6, 5.3Luminosity 2.6, 2.6, 2.6 2.6, 2.6, 2.6Total 6.3, 6.7, 15.3 5.1, 3.9, 8.0energies, including the uncertainties in efficiency correction estimation, background estima-tion, energy scale correction, unfolding, and integrated luminosity, are combined in quadra-ture.
10 Results and discussion
The cross section measurements are first performed separately in the dielectron and dimuondecay channels and then combined using the procedure described in [57]. To assess the sen-sitivity of the measurement to PDF uncertainties, a comparison to theoretical calculations isperformed using
FEWZ d σ /d m measurement The pre-FSR cross section in the full phase space is calculated as σ i = N i u A i (cid:101) i L int , (4)where N i u is the number of events after background subtraction and unfolding procedures fordetector resolution and FSR, A i is the acceptance, and (cid:101) i is the efficiency in a given invariant-mass bin i ; L int is the total integrated luminosity.The cross section in the Z peak region is calculated with Eq. (4) considering the mass region60 < m <
120 GeV.The Z peak cross section measurements in the dielectron and dimuon channels are summa-rized in Table 2. The measurements agree with NNLO theoretical predictions for the full phasespace (i.e., 1137 ±
36 pb, as calculated with
FEWZ ∆ m i .The consistency of the differential cross section measurements obtained in the dielectron and d σ /d m d | y | measurement Table 2: Absolute cross section measurements in the Z peak region (60 < m <
120 GeV). Theuncertainties in the measurements include the experimental and theoretical systematic sourcesand the uncertainty in the integrated luminosity. The statistical component is negligible.Channel Cross sectionDielectron 1141 ±
11 (exp) ±
25 (theo) ±
30 (lumi) pbDimuon 1135 ±
11 (exp) ±
25 (theo) ±
30 (lumi) pbCombined 1138 ± ±
25 (theo) ±
30 (lumi) pbdimuon channels is characterized by a χ probability of 82%, calculated from the total uncer-tainties. Therefore the measurements in the two channels are in agreement and are combinedusing the procedure defined in [57]. Based on the results in the two channels and their sym-metric and positive definite covariance matrices, the estimates of the true cross section valuesare found as unbiased linear combinations of the input measurements having a minimum vari-ance [59]. The uncertainties are considered to be uncorrelated between the two channels, withthe exception of modeling, PDF, and luminosity uncertainties. The effects of correlations be-tween the analysis bins and different systematic sources are taken into account in the combina-tion procedure when constructing the covariance matrix.The result of the DY cross section measurement in the combined channel is presented in Fig. 3.The theoretical prediction makes use of the fixed-order NNLO QCD calculation and the NLOEW correction to DY production initiated by purely weak processes. The G µ input scheme [33]is used to fix the EW parameters in the model. The full spin correlations as well as the γ ∗ /Zinterference effects are included in the calculation. The combined measurement is in agreementwith the NNLO theoretical predictions computed with FEWZ
FEWZ m , m , and m /2, with m corresponding to the middle of the invariant mass bin. Thescale variation uncertainties reach up to 2% and are included in the theoretical error band. d σ /d m d | y | measurement The pre-FSR cross section in bins of the dilepton invariant mass and the absolute value of thedilepton rapidity is measured according to σ ij det = N ij u (cid:101) ij L int . (5)The quantities N ij u and (cid:101) ij are defined in a given bin ( i , j ) , with i corresponding to the binningin dilepton invariant mass and j corresponding to the binning in absolute rapidity. The resultsare divided by the dilepton absolute rapidity bin widths ∆ y j . The acceptance correction to thefull phase space is not applied to the measurement, in order to keep theoretical uncertainties toa minimum.The χ probability characterizing the consistency of the double-differential cross section mea-surements in the two channels is 45% in the entire invariant mass-rapidity range of study. Themeasurements in the two channels are thus in agreement and are combined using the sameprocedure as for the differential cross sections described earlier in the section. Figure 4 showsthe rapidity distribution d σ /d | y | measured in the combined dilepton channel with the predic-tion by FEWZ
10 Results and discussion [GeV] mm m
20 30 40 · · / d m [ pb / G e V ] s d -7 -6 -5 -4 -3 -2 -1
10 110 CMS (8 TeV) mm ee and -1 - m + m , - e + e fi */Z g dataFEWZ, NNLO CT10 m [GeV] D a t a /t heo r y Figure 3: The DY differential cross section as measured in the combined dilepton channel andas predicted by NNLO
FEWZ χ probability characterizing theconsistency of the predicted and measured cross sections is 91% with 41 degrees of freedom,calculated with total uncertainties while taking into account the correlated errors in the twochannels. The uncertainty bands in the theoretical expectations include the statistical and the PDF un-certainties from the
FEWZ
FEWZ χ probability calculated between data and the theoretical expecta-tion with total uncertainties on the combined results in the low-mass region is 16% (76%) forthe CT10 (NNPDF2.1) PDFs. In the Z peak region, the two predictions are relatively close toeach other and agree well with the measurements. The statistical uncertainties in the measure-ments in the highest mass region are of the order of the PDF uncertainty. The corresponding χ probability calculated in the high mass region is 37% (35%) for the CT10 (NNPDF2.1) PDFs. The ratios of the normalized differential and double-differential cross sections for the DY pro-cess at the center-of-mass energies of 7 and 8 TeV in bins of dilepton invariant mass and dileptonabsolute rapidity are presented. The pre-FSR double ratio in bins of invariant mass is calculatedfollowing the prescription introduced in [11] according to R ( pp → γ ∗ /Z → (cid:96) + (cid:96) − ) = (cid:0) σ Z d σ d m (cid:1) ( ) (cid:0) σ Z d σ d m (cid:1) ( ) , (6)while the pre-FSR double ratio in bins of mass and rapidity is calculated as R det ( pp → γ ∗ /Z → (cid:96) + (cid:96) − ) = (cid:0) σ Z d σ d m d | y | (cid:1) ( p T >
10, 20 GeV ) (cid:0) σ Z d σ d m d | y | (cid:1) ( p T >
9, 14 GeV ) , (7)where σ Z is the cross section in the Z peak region; (cid:96) denotes e or µ . The same binning is usedfor differential measurements at 7 and 8 TeV in order to compute the ratios consistently.The double ratio measurements provide a high sensitivity to NNLO QCD effects and couldpotentially yield precise constraints on the PDFs; the theoretical systematic uncertainties in thecross section calculations at different center-of-mass energies have substantial correlations, asdiscussed in Section 9. Due to cancellation in the double ratio, the effect of the γγ -initiatedprocesses is negligible.Figure 5 shows the pre-FSR DY double ratio measurement in the combined (dielectron anddimuon) channel as a function of dilepton invariant mass, for the full phase space. The theo-retical prediction for the double ratio is calculated using FEWZ √ s and the Bjorken x dependenciesof the PDFs, since the dependence on the hard scattering cross section is canceled out. In theZ peak region, the expected double ratio is close to 1 by definition. It increases linearly as afunction of the logarithm of the invariant mass in the region below 200 GeV, where partonswith small Bjorken x contribute the most. The difference in regions of x probed at 7 and 8 TeVcenter-of-mass energies leads to a rapid increase of the double ratio as a function of mass above200 GeV.
10 Results and discussion (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
20 < m < 30 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
30 < m < 45 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
45 < m < 60 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
60 < m < 120 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
120 < m < 200 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y (8 TeV) mm ee and -1 CMS / d | y | [ pb ] s d
200 < m < 1500 GeV
Data FEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| D a t a /t heo r y Figure 4: The DY dilepton rapidity distribution d σ /d | y | within the detector acceptance, plottedfor different mass ranges, as measured in the combined dilepton channel and as predicted byNNLO FEWZ m [GeV] R
20 50 100 200 500 10000
DataFEWZ, NNLO CT10
CMS (8 TeV) mm ee and -1 mm -1 ee, 4.5 fb -1 Figure 5: Measured DY double ratios at center-of-mass energies of 7 and 8 TeV in the combineddilepton channel as compared to NNLO
FEWZ R isgiven in Eq. (6).
11 Summary
The uncertainty bands in the theoretical prediction of the double ratio include the statistical andthe PDF uncertainties from the
FEWZ χ probability from a comparison of the predicted andmeasured double ratios is 87% with 40 degrees of freedom, calculated with the total uncertain-ties. At high mass, the statistical component of the uncertainty becomes significant, primarilyfrom the 7 TeV measurements.The double ratios within the CMS acceptance as measured and as predicted by FEWZ
FEWZ m , m , and m /2, with m corresponding to the middle of the invariant mass bin. Thescale variation uncertainties reach up to 2% and are included in the theoretical error band.The double ratio predictions calculated with the CT10 NNLO and NNPDF2.1 NNLO PDFsagree with the measurements. Below the Z peak, NNPDF2.1 NNLO PDF theoretical predic-tions are in a closer agreement with the measurement. In the Z peak region, a difference inthe slope of both theoretical predictions as compared to the measurement is observed in thecentral absolute rapidity region. In the high-rapidity and high-mass regions, the effect of thelimited number of events in the 7 TeV measurement is significant. In the 120–200 GeV region,the measurement is at the lower edge of the uncertainty band of the theory predictions.The DY double-differential cross section and double ratio measurements presented here canbe used to impose constraints on the quark and antiquark PDFs in a wide range of x , comple-menting the data from the fixed-target experiments with modern collider data.
11 Summary
This paper presents measurements of the Drell–Yan differential cross section d σ /d m and thedouble-differential cross section d σ /d m d | y | with proton-proton collision data collected withthe CMS detector at the LHC at a center-of-mass energy of 8 TeV. In addition, the first mea-surements of the ratios of the normalized differential and double-differential cross sections forthe DY process at center-of-mass energies of 7 and 8 TeV in bins of dilepton invariant mass andabsolute rapidity are presented. A previously published CMS measurement based on 7 TeVdata [12] is used for the double ratio calculations.The measured inclusive cross section in the Z peak region is 1138 ± ±
25 (theo) ±
30 (lumi) pbfor the combination of the dielectron and dimuon channels. This is the most precise mea-surement of the cross section in the Z peak region at √ s = σ /d m andd σ /d m d | y | measurements agree with the NNLO theoretical predictions computed with FEWZ Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
20 < m < 30 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
30 < m < 45 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
45 < m < 60 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
60 < m < 120 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
120 < m < 200 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Absolute dilepton rapidity |y| de t R > 20, 10 GeV) T (8 TeV, p mm ee and -1 T (7 TeV, p mm -1
200 < m < 1500 GeV
CMS
DataFEWZ, NNLO CT10FEWZ, NNLO NNPDF2.1
Figure 6: Measured DY double ratios as a function of the absolute dilepton rapidity within thedetector acceptance, at center-of-mass energies of 7 and 8 TeV, plotted for different mass rangesand as predicted by NNLO
FEWZ R det is given inEq. (7).
11 Summary using the CT10 NNLO and NNPDF2.1 NNLO PDFs. The double ratio measurement agreeswith the theoretical prediction within the systematic and PDF uncertainties.The experimental uncertainties in the double-differential cross section and the double ratiomeasurements presented are relatively small compared to the PDF uncertainties.
Acknowledgments
We congratulate our colleagues in the CERN accelerator departments for the excellent perfor-mance of the LHC and thank the technical and administrative staffs at CERN and at otherCMS institutes for their contributions to the success of the CMS effort. In addition, we grate-fully acknowledge the computing centers and personnel of the Worldwide LHC ComputingGrid for delivering so effectively the computing infrastructure essential to our analyses. Fi-nally, we acknowledge the enduring support for the construction and operation of the LHCand the CMS detector provided by the following funding agencies: the Austrian Federal Min-istry of Science, Research and Economy and the Austrian Science Fund; the Belgian Fonds dela Recherche Scientifique, and Fonds voor Wetenschappelijk Onderzoek; the Brazilian Fund-ing Agencies (CNPq, CAPES, FAPERJ, and FAPESP); the Bulgarian Ministry of Education andScience; CERN; the Chinese Academy of Sciences, Ministry of Science and Technology, and Na-tional Natural Science Foundation of China; the Colombian Funding Agency (COLCIENCIAS);the Croatian Ministry of Science, Education and Sport, and the Croatian Science Foundation;the Research Promotion Foundation, Cyprus; the Ministry of Education and Research, Esto-nian Research Council via IUT23-4 and IUT23-6 and European Regional Development Fund,Estonia; the Academy of Finland, Finnish Ministry of Education and Culture, and HelsinkiInstitute of Physics; the Institut National de Physique Nucl´eaire et de Physique des Partic-ules / CNRS, and Commissariat `a l’ ´Energie Atomique et aux ´Energies Alternatives / CEA,France; the Bundesministerium f ¨ur Bildung und Forschung, Deutsche Forschungsgemeinschaft,and Helmholtz-Gemeinschaft Deutscher Forschungszentren, Germany; the General Secretariatfor Research and Technology, Greece; the National Scientific Research Foundation, and Na-tional Innovation Office, Hungary; the Department of Atomic Energy and the Departmentof Science and Technology, India; the Institute for Studies in Theoretical Physics and Mathe-matics, Iran; the Science Foundation, Ireland; the Istituto Nazionale di Fisica Nucleare, Italy;the Ministry of Science, ICT and Future Planning, and National Research Foundation (NRF),Republic of Korea; the Lithuanian Academy of Sciences; the Ministry of Education, and Uni-versity of Malaya (Malaysia); the Mexican Funding Agencies (CINVESTAV, CONACYT, SEP,and UASLP-FAI); the Ministry of Business, Innovation and Employment, New Zealand; thePakistan Atomic Energy Commission; the Ministry of Science and Higher Education and theNational Science Centre, Poland; the Fundac¸ ˜ao para a Ciˆencia e a Tecnologia, Portugal; JINR,Dubna; the Ministry of Education and Science of the Russian Federation, the Federal Agency ofAtomic Energy of the Russian Federation, Russian Academy of Sciences, and the Russian Foun-dation for Basic Research; the Ministry of Education, Science and Technological Developmentof Serbia; the Secretar´ıa de Estado de Investigaci ´on, Desarrollo e Innovaci ´on and ProgramaConsolider-Ingenio 2010, Spain; the Swiss Funding Agencies (ETH Board, ETH Zurich, PSI,SNF, UniZH, Canton Zurich, and SER); the Ministry of Science and Technology, Taipei; theThailand Center of Excellence in Physics, the Institute for the Promotion of Teaching Scienceand Technology of Thailand, Special Task Force for Activating Research and the National Sci-ence and Technology Development Agency of Thailand; the Scientific and Technical ResearchCouncil of Turkey, and Turkish Atomic Energy Authority; the National Academy of Sciencesof Ukraine, and State Fund for Fundamental Researches, Ukraine; the Science and TechnologyFacilities Council, UK; the US Department of Energy, and the US National Science Foundation. eferences Individuals have received support from the Marie-Curie programme and the European Re-search Council and EPLANET (European Union); the Leventis Foundation; the A. P. SloanFoundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Of-fice; the Fonds pour la Formation `a la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); theMinistry of Education, Youth and Sports (MEYS) of the Czech Republic; the Council of Sci-ence and Industrial Research, India; the HOMING PLUS programme of Foundation for PolishScience, cofinanced from European Union, Regional Development Fund; the Compagnia diSan Paolo (Torino); the Consorzio per la Fisica (Trieste); MIUR project 20108T4XTM (Italy); theThalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF; and the NationalPriorities Research Program by Qatar National Research Fund.
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Institute of High Energy Physics, Beijing, China
J.G. Bian, G.M. Chen, H.S. Chen, M. Chen, T. Cheng, R. Du, C.H. Jiang, R. Plestina , F. Romeo,J. Tao, Z. Wang State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China
C. Asawatangtrakuldee, Y. Ban, Q. Li, S. Liu, Y. Mao, S.J. Qian, D. Wang, Z. Xu, W. Zou
Universidad de Los Andes, Bogota, Colombia
C. Avila, A. Cabrera, L.F. Chaparro Sierra, C. Florez, J.P. Gomez, B. Gomez Moreno,J.C. Sanabria
University of Split, Faculty of Electrical Engineering, Mechanical Engineering and NavalArchitecture, Split, Croatia
N. Godinovic, D. Lelas, D. Polic, I. Puljak
University of Split, Faculty of Science, Split, Croatia
Z. Antunovic, M. Kovac
Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, K. Kadija, J. Luetic, D. Mekterovic, L. Sudic
University of Cyprus, Nicosia, Cyprus
A. Attikis, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis
Charles University, Prague, Czech Republic
M. Bodlak, M. Finger, M. Finger Jr. Academy of Scientific Research and Technology of the Arab Republic of Egypt, EgyptianNetwork of High Energy Physics, Cairo, Egypt
Y. Assran , A. Ellithi Kamel , M.A. Mahmoud , A. Radi National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
M. Kadastik, M. Murumaa, M. Raidal, A. Tiko
Department of Physics, University of Helsinki, Helsinki, Finland
P. Eerola, M. Voutilainen
Helsinki Institute of Physics, Helsinki, Finland
J. H¨ark ¨onen, V. Karim¨aki, R. Kinnunen, M.J. Kortelainen, T. Lamp´en, K. Lassila-Perini, S. Lehti,T. Lind´en, P. Luukka, T. M¨aenp¨a¨a, T. Peltola, E. Tuominen, J. Tuominiemi, E. Tuovinen,L. Wendland
Lappeenranta University of Technology, Lappeenranta, Finland
J. Talvitie, T. Tuuva DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France
M. Besancon, F. Couderc, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, C. Favaro, F. Ferri,S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, E. Locci, J. Malcles,J. Rander, A. Rosowsky, M. Titov
Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
S. Baffioni, F. Beaudette, P. Busson, E. Chapon, C. Charlot, T. Dahms, M. Dalchenko,L. Dobrzynski, N. Filipovic, A. Florent, R. Granier de Cassagnac, L. Mastrolorenzo, P. Min´e,I.N. Naranjo, M. Nguyen, C. Ochando, G. Ortona, P. Paganini, S. Regnard, R. Salerno,J.B. Sauvan, Y. Sirois, C. Veelken, Y. Yilmaz, A. Zabi
Institut Pluridisciplinaire Hubert Curien, Universit´e de Strasbourg, Universit´e de HauteAlsace Mulhouse, CNRS/IN2P3, Strasbourg, France
J.-L. Agram , J. Andrea, A. Aubin, D. Bloch, J.-M. Brom, E.C. Chabert, C. Collard, E. Conte ,J.-C. Fontaine , D. Gel´e, U. Goerlach, C. Goetzmann, A.-C. Le Bihan, K. Skovpen, P. Van Hove Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique des Particules,CNRS/IN2P3, Villeurbanne, France
S. Gadrat
Universit´e de Lyon, Universit´e Claude Bernard Lyon 1, CNRS-IN2P3, Institut de PhysiqueNucl´eaire de Lyon, Villeurbanne, France
S. Beauceron, N. Beaupere, C. Bernet , G. Boudoul , E. Bouvier, S. Brochet, C.A. CarrilloMontoya, J. Chasserat, R. Chierici, D. Contardo , P. Depasse, H. El Mamouni, J. Fan, J. Fay,S. Gascon, M. Gouzevitch, B. Ille, T. Kurca, M. Lethuillier, L. Mirabito, S. Perries, J.D. RuizAlvarez, D. Sabes, L. Sgandurra, V. Sordini, M. Vander Donckt, P. Verdier, S. Viret, H. Xiao Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi,Georgia
Z. Tsamalaidze RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany
C. Autermann, S. Beranek, M. Bontenackels, M. Edelhoff, L. Feld, A. Heister, K. Klein,M. Lipinski, A. Ostapchuk, M. Preuten, F. Raupach, J. Sammet, S. Schael, J.F. Schulte, H. Weber,B. Wittmer, V. Zhukov RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
M. Ata, M. Brodski, E. Dietz-Laursonn, D. Duchardt, M. Erdmann, R. Fischer, A. G ¨uth,T. Hebbeker, C. Heidemann, K. Hoepfner, D. Klingebiel, S. Knutzen, P. Kreuzer,M. Merschmeyer, A. Meyer, P. Millet, M. Olschewski, K. Padeken, P. Papacz, H. Reithler,S.A. Schmitz, L. Sonnenschein, D. Teyssier, S. Th ¨uer, M. Weber
RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
V. Cherepanov, Y. Erdogan, G. Fl ¨ugge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle,B. Kargoll, T. Kress, Y. Kuessel, A. K ¨unsken, J. Lingemann , A. Nowack, I.M. Nugent, O. Pooth,A. Stahl Deutsches Elektronen-Synchrotron, Hamburg, Germany
M. Aldaya Martin, I. Asin, N. Bartosik, J. Behr, U. Behrens, A.J. Bell, A. Bethani, K. Borras,A. Burgmeier, A. Cakir, L. Calligaris, A. Campbell, S. Choudhury, F. Costanza, C. DiezPardos, G. Dolinska, S. Dooling, T. Dorland, G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke,J. Garay Garcia, A. Geiser, P. Gunnellini, J. Hauk, M. Hempel , H. Jung, A. Kalogeropoulos,M. Kasemann, P. Katsas, J. Kieseler, C. Kleinwort, I. Korol, D. Kr ¨ucker, W. Lange, J. Leonard,K. Lipka, A. Lobanov, W. Lohmann , B. Lutz, R. Mankel, I. Marfin , I.-A. Melzer-Pellmann, A The CMS Collaboration
A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, S. Naumann-Emme, A. Nayak, E. Ntomari,H. Perrey, D. Pitzl, R. Placakyte, A. Raspereza, P.M. Ribeiro Cipriano, B. Roland, E. Ron,M. ¨O. Sahin, J. Salfeld-Nebgen, P. Saxena, T. Schoerner-Sadenius, M. Schr ¨oder, C. Seitz,S. Spannagel, A.D.R. Vargas Trevino, R. Walsh, C. Wissing
University of Hamburg, Hamburg, Germany
V. Blobel, M. Centis Vignali, A.R. Draeger, J. Erfle, E. Garutti, K. Goebel, M. G ¨orner, J. Haller,M. Hoffmann, R.S. H ¨oing, A. Junkes, H. Kirschenmann, R. Klanner, R. Kogler, J. Lange,T. Lapsien, T. Lenz, I. Marchesini, J. Ott, T. Peiffer, A. Perieanu, N. Pietsch, J. Poehlsen,T. Poehlsen, D. Rathjens, C. Sander, H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt,M. Seidel, V. Sola, H. Stadie, G. Steinbr ¨uck, D. Troendle, E. Usai, L. Vanelderen, A. Vanhoefer
Institut f ¨ur Experimentelle Kernphysik, Karlsruhe, Germany
C. Barth, C. Baus, J. Berger, C. B ¨oser, E. Butz, T. Chwalek, W. De Boer, A. Descroix, A. Dierlamm,M. Feindt, F. Frensch, M. Giffels, A. Gilbert, F. Hartmann , T. Hauth, U. Husemann, I. Katkov ,A. Kornmayer , P. Lobelle Pardo, M.U. Mozer, T. M ¨uller, Th. M ¨uller, A. N ¨urnberg, G. Quast,K. Rabbertz, S. R ¨ocker, H.J. Simonis, F.M. Stober, R. Ulrich, J. Wagner-Kuhr, S. Wayand,T. Weiler, R. Wolf Institute of Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi,Greece
G. Anagnostou, G. Daskalakis, T. Geralis, V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,A. Markou, C. Markou, A. Psallidas, I. Topsis-Giotis
University of Athens, Athens, Greece
A. Agapitos, S. Kesisoglou, A. Panagiotou, N. Saoulidou, E. Stiliaris
University of Io´annina, Io´annina, Greece
X. Aslanoglou, I. Evangelou, G. Flouris, C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos,E. Paradas, J. Strologas
Wigner Research Centre for Physics, Budapest, Hungary
G. Bencze, C. Hajdu, P. Hidas, D. Horvath , F. Sikler, V. Veszpremi, G. Vesztergombi ,A.J. Zsigmond Institute of Nuclear Research ATOMKI, Debrecen, Hungary
N. Beni, S. Czellar, J. Karancsi , J. Molnar, J. Palinkas, Z. Szillasi University of Debrecen, Debrecen, Hungary
A. Makovec, P. Raics, Z.L. Trocsanyi, B. Ujvari
National Institute of Science Education and Research, Bhubaneswar, India
S.K. Swain
Panjab University, Chandigarh, India
S.B. Beri, V. Bhatnagar, R. Gupta, U.Bhawandeep, A.K. Kalsi, M. Kaur, R. Kumar, M. Mittal,N. Nishu, J.B. Singh
University of Delhi, Delhi, India
Ashok Kumar, Arun Kumar, S. Ahuja, A. Bhardwaj, B.C. Choudhary, A. Kumar, S. Malhotra,M. Naimuddin, K. Ranjan, V. Sharma
Saha Institute of Nuclear Physics, Kolkata, India
S. Banerjee, S. Bhattacharya, K. Chatterjee, S. Dutta, B. Gomber, Sa. Jain, Sh. Jain, R. Khurana,A. Modak, S. Mukherjee, D. Roy, S. Sarkar, M. Sharan9
S. Banerjee, S. Bhattacharya, K. Chatterjee, S. Dutta, B. Gomber, Sa. Jain, Sh. Jain, R. Khurana,A. Modak, S. Mukherjee, D. Roy, S. Sarkar, M. Sharan9 Bhabha Atomic Research Centre, Mumbai, India
A. Abdulsalam, D. Dutta, V. Kumar, A.K. Mohanty , L.M. Pant, P. Shukla, A. Topkar Tata Institute of Fundamental Research, Mumbai, India
T. Aziz, S. Banerjee, S. Bhowmik , R.M. Chatterjee, R.K. Dewanjee, S. Dugad, S. Ganguly,S. Ghosh, M. Guchait, A. Gurtu , G. Kole, S. Kumar, M. Maity , G. Majumder, K. Mazumdar,G.B. Mohanty, B. Parida, K. Sudhakar, N. Wickramage Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
H. Bakhshiansohi, H. Behnamian, S.M. Etesami , A. Fahim , R. Goldouzian, M. Khakzad,M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi,B. Safarzadeh , M. Zeinali University College Dublin, Dublin, Ireland
M. Felcini, M. Grunewald
INFN Sezione di Bari a , Universit`a di Bari b , Politecnico di Bari c , Bari, Italy M. Abbrescia a , b , C. Calabria a , b , S.S. Chhibra a , b , A. Colaleo a , D. Creanza a , c , N. De Filippis a , c ,M. De Palma a , b , L. Fiore a , G. Iaselli a , c , G. Maggi a , c , M. Maggi a , S. My a , c , S. Nuzzo a , b ,A. Pompili a , b , G. Pugliese a , c , R. Radogna a , b ,2 , G. Selvaggi a , b , A. Sharma a , L. Silvestris a ,2 ,R. Venditti a , b , P. Verwilligen a INFN Sezione di Bologna a , Universit`a di Bologna b , Bologna, Italy G. Abbiendi a , A.C. Benvenuti a , D. Bonacorsi a , b , S. Braibant-Giacomelli a , b , L. Brigliadori a , b ,R. Campanini a , b , P. Capiluppi a , b , A. Castro a , b , F.R. Cavallo a , G. Codispoti a , b , M. Cuffiani a , b ,G.M. Dallavalle a , F. Fabbri a , A. Fanfani a , b , D. Fasanella a , b , P. Giacomelli a , C. Grandi a ,L. Guiducci a , b , S. Marcellini a , G. Masetti a , A. Montanari a , F.L. Navarria a , b , A. Perrotta a ,F. Primavera a , b , A.M. Rossi a , b , T. Rovelli a , b , G.P. Siroli a , b , N. Tosi a , b , R. Travaglini a , b INFN Sezione di Catania a , Universit`a di Catania b , CSFNSM c , Catania, Italy S. Albergo a , b , G. Cappello a , M. Chiorboli a , b , S. Costa a , b , F. Giordano a ,2 , R. Potenza a , b ,A. Tricomi a , b , C. Tuve a , b INFN Sezione di Firenze a , Universit`a di Firenze b , Firenze, Italy G. Barbagli a , V. Ciulli a , b , C. Civinini a , R. D’Alessandro a , b , E. Focardi a , b , E. Gallo a , S. Gonzi a , b ,V. Gori a , b , P. Lenzi a , b , M. Meschini a , S. Paoletti a , G. Sguazzoni a , A. Tropiano a , b INFN Laboratori Nazionali di Frascati, Frascati, Italy
L. Benussi, S. Bianco, F. Fabbri, D. Piccolo
INFN Sezione di Genova a , Universit`a di Genova b , Genova, Italy R. Ferretti a , b , F. Ferro a , M. Lo Vetere a , b , E. Robutti a , S. Tosi a , b INFN Sezione di Milano-Bicocca a , Universit`a di Milano-Bicocca b , Milano, Italy M.E. Dinardo a , b , S. Fiorendi a , b , S. Gennai a ,2 , R. Gerosa a , b ,2 , A. Ghezzi a , b , P. Govoni a , b ,M.T. Lucchini a , b ,2 , S. Malvezzi a , R.A. Manzoni a , b , A. Martelli a , b , B. Marzocchi a , b ,2 , D. Menasce a ,L. Moroni a , M. Paganoni a , b , D. Pedrini a , S. Ragazzi a , b , N. Redaelli a , T. Tabarelli de Fatis a , b INFN Sezione di Napoli a , Universit`a di Napoli ’Federico II’ b , Universit`a dellaBasilicata (Potenza) c , Universit`a G. Marconi (Roma) d , Napoli, Italy S. Buontempo a , N. Cavallo a , c , S. Di Guida a , d ,2 , F. Fabozzi a , c , A.O.M. Iorio a , b , L. Lista a ,S. Meola a , d ,2 , M. Merola a , P. Paolucci a ,2 A The CMS Collaboration
INFN Sezione di Padova a , Universit`a di Padova b , Universit`a di Trento (Trento) c , Padova,Italy P. Azzi a , N. Bacchetta a , M. Bellato a , M. Biasotto a ,25 , A. Branca a , b , M. Dall’Osso a , b , T. Dorigo a ,S. Fantinel a , F. Fanzago a , M. Galanti a , b , F. Gasparini a , b , A. Gozzelino a , K. Kanishchev a , c ,S. Lacaprara a , M. Margoni a , b , A.T. Meneguzzo a , b , J. Pazzini a , b , N. Pozzobon a , b , P. Ronchese a , b ,F. Simonetto a , b , E. Torassa a , M. Tosi a , b , S. Vanini a , b , P. Zotto a , b , A. Zucchetta a , b , G. Zumerle a , b INFN Sezione di Pavia a , Universit`a di Pavia b , Pavia, Italy M. Gabusi a , b , S.P. Ratti a , b , V. Re a , C. Riccardi a , b , P. Salvini a , P. Vitulo a , b INFN Sezione di Perugia a , Universit`a di Perugia b , Perugia, Italy M. Biasini a , b , G.M. Bilei a , D. Ciangottini a , b ,2 , L. Fan `o a , b , P. Lariccia a , b , G. Mantovani a , b ,M. Menichelli a , A. Saha a , A. Santocchia a , b , A. Spiezia a , b ,2 INFN Sezione di Pisa a , Universit`a di Pisa b , Scuola Normale Superiore di Pisa c , Pisa, Italy K. Androsov a ,26 , P. Azzurri a , G. Bagliesi a , J. Bernardini a , T. Boccali a , G. Broccolo a , c , R. Castaldi a ,M.A. Ciocci a ,26 , R. Dell’Orso a , S. Donato a , c ,2 , G. Fedi, F. Fiori a , c , L. Fo`a a , c , A. Giassi a ,M.T. Grippo a ,26 , F. Ligabue a , c , T. Lomtadze a , L. Martini a , b , A. Messineo a , b , C.S. Moon a ,27 ,F. Palla a ,2 , A. Rizzi a , b , A. Savoy-Navarro a ,28 , A.T. Serban a , P. Spagnolo a , P. Squillacioti a ,26 ,R. Tenchini a , G. Tonelli a , b , A. Venturi a , P.G. Verdini a , C. Vernieri a , c INFN Sezione di Roma a , Universit`a di Roma b , Roma, Italy L. Barone a , b , F. Cavallari a , G. D’imperio a , b , D. Del Re a , b , M. Diemoz a , C. Jorda a , E. Longo a , b ,F. Margaroli a , b , P. Meridiani a , F. Micheli a , b ,2 , G. Organtini a , b , R. Paramatti a , S. Rahatlou a , b ,C. Rovelli a , F. Santanastasio a , b , L. Soffi a , b , P. Traczyk a , b ,2 INFN Sezione di Torino a , Universit`a di Torino b , Universit`a del Piemonte Orientale (No-vara) c , Torino, Italy N. Amapane a , b , R. Arcidiacono a , c , S. Argiro a , b , M. Arneodo a , c , R. Bellan a , b , C. Biino a ,N. Cartiglia a , S. Casasso a , b ,2 , M. Costa a , b , A. Degano a , b , N. Demaria a , L. Finco a , b ,2 , C. Mariotti a ,S. Maselli a , E. Migliore a , b , V. Monaco a , b , M. Musich a , M.M. Obertino a , c , L. Pacher a , b ,N. Pastrone a , M. Pelliccioni a , G.L. Pinna Angioni a , b , A. Potenza a , b , A. Romero a , b , M. Ruspa a , c ,R. Sacchi a , b , A. Solano a , b , A. Staiano a , U. Tamponi a INFN Sezione di Trieste a , Universit`a di Trieste b , Trieste, Italy S. Belforte a , V. Candelise a , b ,2 , M. Casarsa a , F. Cossutti a , G. Della Ricca a , b , B. Gobbo a , C. LaLicata a , b , M. Marone a , b , A. Schizzi a , b , T. Umer a , b , A. Zanetti a Kangwon National University, Chunchon, Korea
S. Chang, A. Kropivnitskaya, S.K. Nam
Kyungpook National University, Daegu, Korea
D.H. Kim, G.N. Kim, M.S. Kim, D.J. Kong, S. Lee, Y.D. Oh, H. Park, A. Sakharov, D.C. Son
Chonbuk National University, Jeonju, Korea
T.J. Kim, M.S. Ryu
Chonnam National University, Institute for Universe and Elementary Particles, Kwangju,Korea
J.Y. Kim, D.H. Moon, S. Song
Korea University, Seoul, Korea
S. Choi, D. Gyun, B. Hong, M. Jo, H. Kim, Y. Kim, B. Lee, K.S. Lee, S.K. Park, Y. Roh Seoul National University, Seoul, Korea
H.D. Yoo
University of Seoul, Seoul, Korea
M. Choi, J.H. Kim, I.C. Park, G. Ryu
Sungkyunkwan University, Suwon, Korea
Y. Choi, Y.K. Choi, J. Goh, D. Kim, E. Kwon, J. Lee, I. Yu
Vilnius University, Vilnius, Lithuania
A. Juodagalvis
National Centre for Particle Physics, Universiti Malaya, Kuala Lumpur, Malaysia
J.R. Komaragiri, M.A.B. Md Ali
Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico
E. Casimiro Linares, H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz,A. Hernandez-Almada, R. Lopez-Fernandez, A. Sanchez-Hernandez
Universidad Iberoamericana, Mexico City, Mexico
S. Carrillo Moreno, F. Vazquez Valencia
Benemerita Universidad Autonoma de Puebla, Puebla, Mexico
I. Pedraza, H.A. Salazar Ibarguen
Universidad Aut ´onoma de San Luis Potos´ı, San Luis Potos´ı, Mexico
A. Morelos Pineda
University of Auckland, Auckland, New Zealand
D. Krofcheck
University of Canterbury, Christchurch, New Zealand
P.H. Butler, S. Reucroft
National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
A. Ahmad, M. Ahmad, Q. Hassan, H.R. Hoorani, W.A. Khan, T. Khurshid, M. Shoaib
National Centre for Nuclear Research, Swierk, Poland
H. Bialkowska, M. Bluj, B. Boimska, T. Frueboes, M. G ´orski, M. Kazana, K. Nawrocki,K. Romanowska-Rybinska, M. Szleper, P. Zalewski
Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland
G. Brona, K. Bunkowski, M. Cwiok, W. Dominik, K. Doroba, A. Kalinowski, M. Konecki,J. Krolikowski, M. Misiura, M. Olszewski
Laborat ´orio de Instrumenta¸c˜ao e F´ısica Experimental de Part´ıculas, Lisboa, Portugal
P. Bargassa, C. Beir˜ao Da Cruz E Silva, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro, L. LloretIglesias, F. Nguyen, J. Rodrigues Antunes, J. Seixas, J. Varela, P. Vischia
Joint Institute for Nuclear Research, Dubna, Russia
S. Afanasiev, P. Bunin, M. Gavrilenko, I. Golutvin, I. Gorbunov, A. Kamenev, V. Karjavin,V. Konoplyanikov, A. Lanev, A. Malakhov, V. Matveev , P. Moisenz, V. Palichik, V. Perelygin,S. Shmatov, N. Skatchkov, V. Smirnov, A. Zarubin Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia
V. Golovtsov, Y. Ivanov, V. Kim , E. Kuznetsova, P. Levchenko, V. Murzin, V. Oreshkin,I. Smirnov, V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev, An. Vorobyev A The CMS Collaboration
Institute for Nuclear Research, Moscow, Russia
Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov, A. Pashenkov,D. Tlisov, A. Toropin
Institute for Theoretical and Experimental Physics, Moscow, Russia
V. Epshteyn, V. Gavrilov, N. Lychkovskaya, V. Popov, I. Pozdnyakov, G. Safronov, S. Semenov,A. Spiridonov, V. Stolin, E. Vlasov, A. Zhokin
P.N. Lebedev Physical Institute, Moscow, Russia
V. Andreev, M. Azarkin , I. Dremin , M. Kirakosyan, A. Leonidov , G. Mesyats, S.V. Rusakov,A. Vinogradov Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow,Russia
A. Belyaev, E. Boos, V. Bunichev, M. Dubinin , L. Dudko, A. Ershov, V. Klyukhin, O. Kodolova,I. Lokhtin, S. Obraztsov, M. Perfilov, V. Savrin, A. Snigirev State Research Center of Russian Federation, Institute for High Energy Physics, Protvino,Russia
I. Azhgirey, I. Bayshev, S. Bitioukov, V. Kachanov, A. Kalinin, D. Konstantinov, V. Krychkine,V. Petrov, R. Ryutin, A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov
University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade,Serbia
P. Adzic , M. Ekmedzic, J. Milosevic, V. Rekovic Centro de Investigaciones Energ´eticas Medioambientales y Tecnol ´ogicas (CIEMAT),Madrid, Spain
J. Alcaraz Maestre, C. Battilana, E. Calvo, M. Cerrada, M. Chamizo Llatas, N. Colino, B. De LaCruz, A. Delgado Peris, D. Dom´ınguez V´azquez, A. Escalante Del Valle, C. Fernandez Bedoya,J.P. Fern´andez Ramos, J. Flix, M.C. Fouz, P. Garcia-Abia, O. Gonzalez Lopez, S. Goy Lopez,J.M. Hernandez, M.I. Josa, E. Navarro De Martino, A. P´erez-Calero Yzquierdo, J. Puerta Pelayo,A. Quintario Olmeda, I. Redondo, L. Romero, M.S. Soares
Universidad Aut ´onoma de Madrid, Madrid, Spain
C. Albajar, J.F. de Troc ´oniz, M. Missiroli, D. Moran
Universidad de Oviedo, Oviedo, Spain
H. Brun, J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero
Instituto de F´ısica de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain
J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, J. Duarte Campderros, M. Fernandez,G. Gomez, A. Graziano, A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, F. Matorras,F.J. Munoz Sanchez, J. Piedra Gomez, T. Rodrigo, A.Y. Rodr´ıguez-Marrero, A. Ruiz-Jimeno,L. Scodellaro, I. Vila, R. Vilar Cortabitarte
CERN, European Organization for Nuclear Research, Geneva, Switzerland
D. Abbaneo, E. Auffray, G. Auzinger, M. Bachtis, P. Baillon, A.H. Ball, D. Barney, A. Benaglia,J. Bendavid, L. Benhabib, J.F. Benitez, P. Bloch, A. Bocci, A. Bonato, O. Bondu, C. Botta,H. Breuker, T. Camporesi, G. Cerminara, S. Colafranceschi , M. D’Alfonso, D. d’Enterria,A. Dabrowski, A. David, F. De Guio, A. De Roeck, S. De Visscher, E. Di Marco, M. Dobson,M. Dordevic, B. Dorney, N. Dupont-Sagorin, A. Elliott-Peisert, G. Franzoni, W. Funk, D. Gigi,K. Gill, D. Giordano, M. Girone, F. Glege, R. Guida, S. Gundacker, M. Guthoff, J. Hammer,M. Hansen, P. Harris, J. Hegeman, V. Innocente, P. Janot, K. Kousouris, K. Krajczar, P. Lecoq, C. Lourenc¸o, N. Magini, L. Malgeri, M. Mannelli, J. Marrouche, L. Masetti, F. Meijers, S. Mersi,E. Meschi, F. Moortgat, S. Morovic, M. Mulders, L. Orsini, L. Pape, E. Perez, A. Petrilli,G. Petrucciani, A. Pfeiffer, M. Pimi¨a, D. Piparo, M. Plagge, A. Racz, J. Rojo, G. Rolandi ,M. Rovere, H. Sakulin, C. Sch¨afer, C. Schwick, A. Sharma, P. Siegrist, P. Silva, M. Simon,P. Sphicas , D. Spiga, J. Steggemann, B. Stieger, M. Stoye, Y. Takahashi, D. Treille, A. Tsirou,G.I. Veres , N. Wardle, H.K. W ¨ohri, H. Wollny, W.D. Zeuner Paul Scherrer Institut, Villigen, Switzerland
W. Bertl, K. Deiters, W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski,U. Langenegger, D. Renker, T. Rohe
Institute for Particle Physics, ETH Zurich, Zurich, Switzerland
F. Bachmair, L. B¨ani, L. Bianchini, M.A. Buchmann, B. Casal, N. Chanon, G. Dissertori,M. Dittmar, M. Doneg`a, M. D ¨unser, P. Eller, C. Grab, D. Hits, J. Hoss, W. Lustermann,B. Mangano, A.C. Marini, M. Marionneau, P. Martinez Ruiz del Arbol, M. Masciovecchio,D. Meister, N. Mohr, P. Musella, C. N¨ageli , F. Nessi-Tedaldi, F. Pandolfi, F. Pauss, L. Perrozzi,M. Peruzzi, M. Quittnat, L. Rebane, M. Rossini, A. Starodumov , M. Takahashi, K. Theofilatos,R. Wallny, H.A. Weber Universit¨at Z ¨urich, Zurich, Switzerland
C. Amsler , M.F. Canelli, V. Chiochia, A. De Cosa, A. Hinzmann, T. Hreus, B. Kilminster,C. Lange, B. Millan Mejias, J. Ngadiuba, D. Pinna, P. Robmann, F.J. Ronga, S. Taroni, M. Verzetti,Y. Yang National Central University, Chung-Li, Taiwan
M. Cardaci, K.H. Chen, C. Ferro, C.M. Kuo, W. Lin, Y.J. Lu, R. Volpe, S.S. Yu
National Taiwan University (NTU), Taipei, Taiwan
P. Chang, Y.H. Chang, Y. Chao, K.F. Chen, P.H. Chen, C. Dietz, U. Grundler, W.-S. Hou, Y.F. Liu,R.-S. Lu, E. Petrakou, Y.M. Tzeng, R. Wilken
Chulalongkorn University, Faculty of Science, Department of Physics, Bangkok, Thailand
B. Asavapibhop, G. Singh, N. Srimanobhas, N. Suwonjandee
Cukurova University, Adana, Turkey
A. Adiguzel, M.N. Bakirci , S. Cerci , C. Dozen, I. Dumanoglu, E. Eskut, S. Girgis,G. Gokbulut, Y. Guler, E. Gurpinar, I. Hos, E.E. Kangal, A. Kayis Topaksu, G. Onengut ,K. Ozdemir, S. Ozturk , A. Polatoz, D. Sunar Cerci , B. Tali , H. Topakli , M. Vergili,C. Zorbilmez Middle East Technical University, Physics Department, Ankara, Turkey
I.V. Akin, B. Bilin, S. Bilmis, H. Gamsizkan , B. Isildak , G. Karapinar , K. Ocalan ,S. Sekmen, U.E. Surat, M. Yalvac, M. Zeyrek Bogazici University, Istanbul, Turkey
E.A. Albayrak , E. G ¨ulmez, M. Kaya , O. Kaya , T. Yetkin Istanbul Technical University, Istanbul, Turkey
K. Cankocak, F.I. Vardarlı
National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine
L. Levchuk, P. Sorokin
University of Bristol, Bristol, United Kingdom
J.J. Brooke, E. Clement, D. Cussans, H. Flacher, J. Goldstein, M. Grimes, G.P. Heath, H.F. Heath, A The CMS Collaboration
J. Jacob, L. Kreczko, C. Lucas, Z. Meng, D.M. Newbold , S. Paramesvaran, A. Poll, T. Sakuma,S. Seif El Nasr-storey, S. Senkin, V.J. Smith Rutherford Appleton Laboratory, Didcot, United Kingdom
K.W. Bell, A. Belyaev , C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Coughlan, K. Harder,S. Harper, E. Olaiya, D. Petyt, C.H. Shepherd-Themistocleous, A. Thea, I.R. Tomalin,T. Williams, W.J. Womersley, S.D. Worm Imperial College, London, United Kingdom
M. Baber, R. Bainbridge, O. Buchmuller, D. Burton, D. Colling, N. Cripps, P. Dauncey,G. Davies, M. Della Negra, P. Dunne, W. Ferguson, J. Fulcher, D. Futyan, G. Hall, G. Iles,M. Jarvis, G. Karapostoli, M. Kenzie, R. Lane, R. Lucas , L. Lyons, A.-M. Magnan, S. Malik,B. Mathias, J. Nash, A. Nikitenko , J. Pela, M. Pesaresi, K. Petridis, D.M. Raymond,S. Rogerson, A. Rose, C. Seez, P. Sharp † , A. Tapper, M. Vazquez Acosta, T. Virdee, S.C. Zenz Brunel University, Uxbridge, United Kingdom
J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, D. Leggat, D. Leslie, I.D. Reid, P. Symonds,L. Teodorescu, M. Turner
Baylor University, Waco, USA
J. Dittmann, K. Hatakeyama, A. Kasmi, H. Liu, T. Scarborough, Z. Wu
The University of Alabama, Tuscaloosa, USA
O. Charaf, S.I. Cooper, C. Henderson, P. Rumerio
Boston University, Boston, USA
A. Avetisyan, T. Bose, C. Fantasia, P. Lawson, C. Richardson, J. Rohlf, J. St. John, L. Sulak
Brown University, Providence, USA
J. Alimena, E. Berry, S. Bhattacharya, G. Christopher, D. Cutts, Z. Demiragli, N. Dhingra,A. Ferapontov, A. Garabedian, U. Heintz, G. Kukartsev, E. Laird, G. Landsberg, M. Luk,M. Narain, M. Segala, T. Sinthuprasith, T. Speer, J. Swanson
University of California, Davis, Davis, USA
R. Breedon, G. Breto, M. Calderon De La Barca Sanchez, S. Chauhan, M. Chertok, J. Conway,R. Conway, P.T. Cox, R. Erbacher, M. Gardner, W. Ko, R. Lander, M. Mulhearn, D. Pellett, J. Pilot,F. Ricci-Tam, S. Shalhout, J. Smith, M. Squires, D. Stolp, M. Tripathi, S. Wilbur, R. Yohay
University of California, Los Angeles, USA
R. Cousins, P. Everaerts, C. Farrell, J. Hauser, M. Ignatenko, G. Rakness, E. Takasugi, V. Valuev,M. Weber
University of California, Riverside, Riverside, USA
K. Burt, R. Clare, J. Ellison, J.W. Gary, G. Hanson, J. Heilman, M. Ivova Rikova, P. Jandir,E. Kennedy, F. Lacroix, O.R. Long, A. Luthra, M. Malberti, M. Olmedo Negrete, A. Shrinivas,S. Sumowidagdo, S. Wimpenny
University of California, San Diego, La Jolla, USA
J.G. Branson, G.B. Cerati, S. Cittolin, R.T. D’Agnolo, A. Holzner, R. Kelley, D. Klein, J. Letts,I. Macneill, D. Olivito, S. Padhi, C. Palmer, M. Pieri, M. Sani, V. Sharma, S. Simon, M. Tadel,Y. Tu, A. Vartak, C. Welke, F. W ¨urthwein, A. Yagil
University of California, Santa Barbara, Santa Barbara, USA
D. Barge, J. Bradmiller-Feld, C. Campagnari, T. Danielson, A. Dishaw, V. Dutta, K. Flowers, M. Franco Sevilla, P. Geffert, C. George, F. Golf, L. Gouskos, J. Incandela, C. Justus, N. Mccoll,J. Richman, D. Stuart, W. To, C. West, J. Yoo
California Institute of Technology, Pasadena, USA
A. Apresyan, A. Bornheim, J. Bunn, Y. Chen, J. Duarte, A. Mott, H.B. Newman, C. Pena,M. Pierini, M. Spiropulu, J.R. Vlimant, R. Wilkinson, S. Xie, R.Y. Zhu
Carnegie Mellon University, Pittsburgh, USA
V. Azzolini, A. Calamba, B. Carlson, T. Ferguson, Y. Iiyama, M. Paulini, J. Russ, H. Vogel,I. Vorobiev
University of Colorado at Boulder, Boulder, USA
J.P. Cumalat, W.T. Ford, A. Gaz, M. Krohn, E. Luiggi Lopez, U. Nauenberg, J.G. Smith,K. Stenson, S.R. Wagner
Cornell University, Ithaca, USA
J. Alexander, A. Chatterjee, J. Chaves, J. Chu, S. Dittmer, N. Eggert, N. Mirman, G. NicolasKaufman, J.R. Patterson, A. Ryd, E. Salvati, L. Skinnari, W. Sun, W.D. Teo, J. Thom,J. Thompson, J. Tucker, Y. Weng, L. Winstrom, P. Wittich
Fairfield University, Fairfield, USA
D. Winn
Fermi National Accelerator Laboratory, Batavia, USA
S. Abdullin, M. Albrow, J. Anderson, G. Apollinari, L.A.T. Bauerdick, A. Beretvas, J. Berryhill,P.C. Bhat, G. Bolla, K. Burkett, J.N. Butler, H.W.K. Cheung, F. Chlebana, S. Cihangir, V.D. Elvira,I. Fisk, J. Freeman, E. Gottschalk, L. Gray, D. Green, S. Gr ¨unendahl, O. Gutsche, J. Hanlon,D. Hare, R.M. Harris, J. Hirschauer, B. Hooberman, S. Jindariani, M. Johnson, U. Joshi,B. Klima, B. Kreis, S. Kwan † , J. Linacre, D. Lincoln, R. Lipton, T. Liu, J. Lykken, K. Maeshima,J.M. Marraffino, V.I. Martinez Outschoorn, S. Maruyama, D. Mason, P. McBride, P. Merkel,K. Mishra, S. Mrenna, S. Nahn, C. Newman-Holmes, V. O’Dell, O. Prokofyev, E. Sexton-Kennedy, S. Sharma, A. Soha, W.J. Spalding, L. Spiegel, L. Taylor, S. Tkaczyk, N.V. Tran,L. Uplegger, E.W. Vaandering, R. Vidal, A. Whitbeck, J. Whitmore, F. Yang University of Florida, Gainesville, USA
D. Acosta, P. Avery, P. Bortignon, D. Bourilkov, M. Carver, D. Curry, S. Das, M. De Gruttola,G.P. Di Giovanni, R.D. Field, M. Fisher, I.K. Furic, J. Hugon, J. Konigsberg, A. Korytov,T. Kypreos, J.F. Low, K. Matchev, H. Mei, P. Milenovic , G. Mitselmakher, L. Muniz,A. Rinkevicius, L. Shchutska, M. Snowball, D. Sperka, J. Yelton, M. Zakaria Florida International University, Miami, USA
S. Hewamanage, S. Linn, P. Markowitz, G. Martinez, J.L. Rodriguez
Florida State University, Tallahassee, USA
T. Adams, A. Askew, J. Bochenek, B. Diamond, J. Haas, S. Hagopian, V. Hagopian, K.F. Johnson,H. Prosper, V. Veeraraghavan, M. Weinberg
Florida Institute of Technology, Melbourne, USA
M.M. Baarmand, M. Hohlmann, H. Kalakhety, F. Yumiceva
University of Illinois at Chicago (UIC), Chicago, USA
M.R. Adams, L. Apanasevich, D. Berry, R.R. Betts, I. Bucinskaite, R. Cavanaugh, O. Evdokimov,L. Gauthier, C.E. Gerber, D.J. Hofman, P. Kurt, C. O’Brien, I.D. Sandoval Gonzalez,C. Silkworth, P. Turner, N. Varelas A The CMS Collaboration
The University of Iowa, Iowa City, USA
B. Bilki , W. Clarida, K. Dilsiz, M. Haytmyradov, J.-P. Merlo, H. Mermerkaya ,A. Mestvirishvili, A. Moeller, J. Nachtman, H. Ogul, Y. Onel, F. Ozok , A. Penzo, R. Rahmat,S. Sen, P. Tan, E. Tiras, J. Wetzel, K. Yi Johns Hopkins University, Baltimore, USA
I. Anderson, B.A. Barnett, B. Blumenfeld, S. Bolognesi, D. Fehling, A.V. Gritsan, P. Maksimovic,C. Martin, M. Swartz
The University of Kansas, Lawrence, USA
P. Baringer, A. Bean, G. Benelli, C. Bruner, J. Gray, R.P. Kenny III, D. Majumder, M. Malek,M. Murray, D. Noonan, S. Sanders, J. Sekaric, R. Stringer, Q. Wang, J.S. Wood
Kansas State University, Manhattan, USA
I. Chakaberia, A. Ivanov, K. Kaadze, S. Khalil, M. Makouski, Y. Maravin, L.K. Saini,N. Skhirtladze, I. Svintradze
Lawrence Livermore National Laboratory, Livermore, USA
J. Gronberg, D. Lange, F. Rebassoo, D. Wright
University of Maryland, College Park, USA
A. Baden, A. Belloni, B. Calvert, S.C. Eno, J.A. Gomez, N.J. Hadley, R.G. Kellogg, T. Kolberg,Y. Lu, A.C. Mignerey, K. Pedro, A. Skuja, M.B. Tonjes, S.C. Tonwar
Massachusetts Institute of Technology, Cambridge, USA
A. Apyan, R. Barbieri, W. Busza, I.A. Cali, M. Chan, L. Di Matteo, G. Gomez Ceballos,M. Goncharov, D. Gulhan, M. Klute, Y.S. Lai, Y.-J. Lee, A. Levin, P.D. Luckey, C. Paus, D. Ralph,C. Roland, G. Roland, G.S.F. Stephans, K. Sumorok, D. Velicanu, J. Veverka, B. Wyslouch,M. Yang, M. Zanetti, V. Zhukova
University of Minnesota, Minneapolis, USA
B. Dahmes, A. Gude, S.C. Kao, K. Klapoetke, Y. Kubota, J. Mans, S. Nourbakhsh, N. Pastika,R. Rusack, A. Singovsky, N. Tambe, J. Turkewitz
University of Mississippi, Oxford, USA
J.G. Acosta, S. Oliveros
University of Nebraska-Lincoln, Lincoln, USA
E. Avdeeva, K. Bloom, S. Bose, D.R. Claes, A. Dominguez, R. Gonzalez Suarez, J. Keller,D. Knowlton, I. Kravchenko, J. Lazo-Flores, F. Meier, F. Ratnikov, G.R. Snow, M. Zvada
State University of New York at Buffalo, Buffalo, USA
J. Dolen, A. Godshalk, I. Iashvili, A. Kharchilava, A. Kumar, S. Rappoccio
Northeastern University, Boston, USA
G. Alverson, E. Barberis, D. Baumgartel, M. Chasco, A. Massironi, D.M. Morse, D. Nash,T. Orimoto, D. Trocino, R.-J. Wang, D. Wood, J. Zhang
Northwestern University, Evanston, USA
K.A. Hahn, A. Kubik, N. Mucia, N. Odell, B. Pollack, A. Pozdnyakov, M. Schmitt, S. Stoynev,K. Sung, M. Velasco, S. Won
University of Notre Dame, Notre Dame, USA
A. Brinkerhoff, K.M. Chan, A. Drozdetskiy, M. Hildreth, C. Jessop, D.J. Karmgard, N. Kellams,K. Lannon, S. Lynch, N. Marinelli, Y. Musienko , T. Pearson, M. Planer, R. Ruchti, G. Smith,N. Valls, M. Wayne, M. Wolf, A. Woodard The Ohio State University, Columbus, USA
L. Antonelli, J. Brinson, B. Bylsma, L.S. Durkin, S. Flowers, A. Hart, C. Hill, R. Hughes,K. Kotov, T.Y. Ling, W. Luo, D. Puigh, M. Rodenburg, B.L. Winer, H. Wolfe, H.W. Wulsin
Princeton University, Princeton, USA
O. Driga, P. Elmer, J. Hardenbrook, P. Hebda, S.A. Koay, P. Lujan, D. Marlow, T. Medvedeva,M. Mooney, J. Olsen, P. Pirou´e, X. Quan, H. Saka, D. Stickland , C. Tully, J.S. Werner,A. Zuranski University of Puerto Rico, Mayaguez, USA
E. Brownson, S. Malik, H. Mendez, J.E. Ramirez Vargas
Purdue University, West Lafayette, USA
V.E. Barnes, D. Benedetti, D. Bortoletto, M. De Mattia, L. Gutay, Z. Hu, M.K. Jha, M. Jones,K. Jung, M. Kress, N. Leonardo, D.H. Miller, N. Neumeister, B.C. Radburn-Smith, X. Shi,I. Shipsey, D. Silvers, A. Svyatkovskiy, F. Wang, W. Xie, L. Xu, J. Zablocki
Purdue University Calumet, Hammond, USA
N. Parashar, J. Stupak
Rice University, Houston, USA
A. Adair, B. Akgun, K.M. Ecklund, F.J.M. Geurts, W. Li, B. Michlin, B.P. Padley, R. Redjimi,J. Roberts, J. Zabel
University of Rochester, Rochester, USA
B. Betchart, A. Bodek, R. Covarelli, P. de Barbaro, R. Demina, Y. Eshaq, T. Ferbel, A. Garcia-Bellido, P. Goldenzweig, J. Han, A. Harel, O. Hindrichs, A. Khukhunaishvili, S. Korjenevski,G. Petrillo, D. Vishnevskiy
The Rockefeller University, New York, USA
R. Ciesielski, L. Demortier, K. Goulianos, C. Mesropian
Rutgers, The State University of New Jersey, Piscataway, USA
S. Arora, A. Barker, J.P. Chou, C. Contreras-Campana, E. Contreras-Campana, D. Duggan,D. Ferencek, Y. Gershtein, R. Gray, E. Halkiadakis, D. Hidas, S. Kaplan, A. Lath, S. Panwalkar,M. Park, R. Patel, S. Salur, S. Schnetzer, D. Sheffield, S. Somalwar, R. Stone, S. Thomas,P. Thomassen, M. Walker
University of Tennessee, Knoxville, USA
K. Rose, S. Spanier, A. York
Texas A&M University, College Station, USA
O. Bouhali , A. Castaneda Hernandez, R. Eusebi, W. Flanagan, J. Gilmore, T. Kamon ,V. Khotilovich, V. Krutelyov, R. Montalvo, I. Osipenkov, Y. Pakhotin, A. Perloff, J. Roe, A. Rose,A. Safonov, I. Suarez, A. Tatarinov, K.A. Ulmer Texas Tech University, Lubbock, USA
N. Akchurin, C. Cowden, J. Damgov, C. Dragoiu, P.R. Dudero, J. Faulkner, K. Kovitanggoon,S. Kunori, S.W. Lee, T. Libeiro, I. Volobouev
Vanderbilt University, Nashville, USA
E. Appelt, A.G. Delannoy, S. Greene, A. Gurrola, W. Johns, C. Maguire, Y. Mao, A. Melo,M. Sharma, P. Sheldon, B. Snook, S. Tuo, J. Velkovska A The CMS Collaboration
University of Virginia, Charlottesville, USA
M.W. Arenton, S. Boutle, B. Cox, B. Francis, J. Goodell, R. Hirosky, A. Ledovskoy, H. Li, C. Lin,C. Neu, J. Wood
Wayne State University, Detroit, USA
C. Clarke, R. Harr, P.E. Karchin, C. Kottachchi Kankanamge Don, P. Lamichhane, J. Sturdy
University of Wisconsin, Madison, USA
D.A. Belknap, D. Carlsmith, M. Cepeda, S. Dasu, L. Dodd, S. Duric, E. Friis, R. Hall-Wilton, M. Herndon, A. Herv´e, P. Klabbers, A. Lanaro, C. Lazaridis, A. Levine, R. Loveless,A. Mohapatra, I. Ojalvo, T. Perry, G.A. Pierro, G. Polese, I. Ross, T. Sarangi, A. Savin,W.H. Smith, D. Taylor, C. Vuosalo, N. Woods † : Deceased1: Also at Vienna University of Technology, Vienna, Austria2: Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland3: Also at Institut Pluridisciplinaire Hubert Curien, Universit´e de Strasbourg, Universit´e deHaute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France4: Also at National Institute of Chemical Physics and Biophysics, Tallinn, Estonia5: Also at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University,Moscow, Russia6: Also at Universidade Estadual de Campinas, Campinas, Brazil7: Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France8: Also at Joint Institute for Nuclear Research, Dubna, Russia9: Also at Suez University, Suez, Egypt10: Also at Cairo University, Cairo, Egypt11: Also at Fayoum University, El-Fayoum, Egypt12: Also at Ain Shams University, Cairo, Egypt13: Now at Sultan Qaboos University, Muscat, Oman14: Also at Universit´e de Haute Alsace, Mulhouse, France15: Also at Brandenburg University of Technology, Cottbus, Germany16: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary17: Also at E ¨otv ¨os Lor´and University, Budapest, Hungary18: Also at University of Debrecen, Debrecen, Hungary19: Also at University of Visva-Bharati, Santiniketan, India20: Now at King Abdulaziz University, Jeddah, Saudi Arabia21: Also at University of Ruhuna, Matara, Sri Lanka22: Also at Isfahan University of Technology, Isfahan, Iran23: Also at University of Tehran, Department of Engineering Science, Tehran, Iran24: Also at Plasma Physics Research Center, Science and Research Branch, Islamic AzadUniversity, Tehran, Iran25: Also at Laboratori Nazionali di Legnaro dell’INFN, Legnaro, Italy26: Also at Universit`a degli Studi di Siena, Siena, Italy27: Also at Centre National de la Recherche Scientifique (CNRS) - IN2P3, Paris, France28: Also at Purdue University, West Lafayette, USA29: Also at Institute for Nuclear Research, Moscow, Russia30: Also at St. Petersburg State Polytechnical University, St. Petersburg, Russia31: Also at National Research Nuclear University "Moscow Engineering PhysicsInstitute" (MEPhI), Moscow, Russia32: Also at California Institute of Technology, Pasadena, USA33: Also at Faculty of Physics, University of Belgrade, Belgrade, Serbia9