T. N. Addy

Measurement of the Azimuthal Angle Dependence of Inclusive Jet Yields in Pb+Pb Collisions at √sNN = 2.76 TeV with the ATLAS Detector

Measurements of the variation of inclusive jet suppression as a function of relative azimuthal angle, Δφ, with respect to the elliptic event plane provide insight into the path-length dependence of jet quenching. ATLAS has measured the Δφ dependence of jet yields in 0.14 nb(-1) of √(s(NN))=2.76 TeV Pb+Pb collisions at the LHC for jet transverse momenta p(T)>45 GeV in different collision centrality bins using an underlying event subtraction procedure that accounts for elliptic flow. The variation of the jet yield with Δφ was characterized by the parameter, v(2)(jet), and the ratio of out-of-plane (Δφ~π/2) to in-plane (Δφ~0) yields. Nonzero v(2)(jet) values were measured in all centrality bins for p(T)<160 GeV. The jet yields are observed to vary by as much as 20% between in-plane and out-of-plane directions.

Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at root s=7 TeV with the ATLAS detector

This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of p(T) in the range 4 < p(T) < 100 GeV and within pseudorapidity vertical bar eta vertical bar < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < p(T) < 26 GeV and within vertical bar eta vertical bar < 2.0, excluding 1.37 < vertical bar eta vertical bar < 1.52. Integrated luminosities of 1.3 pb(-1) and 1.4 pb(-1) are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-p(T) resummation, and to be sensitive to the effects of NLL resummation

Measurement of the cross section for the production of a W boson in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector

A measurement is presented of the cross section for the produ cti n of aW boson with one or two jets, of which at least one must be a b-jet, in pp collisions at √ s = 7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb −1of data collected with the ATLAS detector at the LHC. The W+b-jet cross section is defined for jets reconstructed with the anti -kt clustering algorithm with transverse momentum above 25 GeV and rapidity within±2.1. Theb-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay chan nel of theW boson and is found to be 10.2 ± 1.9 (stat) ± 2.6 (syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent wit h, the measured value.

Search for dark matter in events with a Z boson and missing transverse momentum in pp collisions at root s=8 TeV with ATLAS detector

A search is presented for production of dark-matter particles recoiling against a leptonically decaying Z boson in 20.3 fb(-1) of pp collisions at root s = 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely charged electrons or muons consistent with the decay of a Z boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark-matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with Z bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle.A search is presented for production of dark matter particles recoiling against a leptonically decaying Z boson in 20.3 fb−1 of pp collisions at √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely-charged electrons or muons consistent with the decay of a Z boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with Z bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle. c

Search for new phenomena in the WW???l??l???????? final state in pp collisions at s=7TeV with the ATLAS detector

This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb−1. WW → lνlν ′ (l, l = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. Search for new phenomena in the WW → lνlν final state in pp collisions at √ s = 7 TeV with the ATLAS detector The ATLAS Collaboration (Dated: May 2, 2014) This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb. WW → lνl′ν′ (l, l′ = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. PACS numbers: 14.70.Kv, 04.60.Kz, 12.60.Cn The existence of new phenomena can be probed by studying heavy gauge boson pair production. Heavy particles that can decay to gauge boson pairs are predicted in many scenarios of physics beyond the Standard Model (SM), including the Extended Gauge Model (EGM) [1], Extra Dimensions [2–6], and Technicolor models [7–9]. This paper describes a search for resonant WW production in the WW → lνlν (l, l = e or μ) decay channel using a data sample corresponding to an integrated luminosity of 4.7 fb, collected by the ATLAS detector during 2011 at a center-of-mass energy of 7 TeV. A spin2 Randall-Sundrum (RS) graviton model [2] and one of its extensions, the bulk RS graviton model [10], are used as benchmarks to interpret the analysis result. The original RS model (RS1) was proposed to solve the hierarchy problem. It postulates a warped 5-dimensional universe, where the SM particles are localized on the TeV brane and the graviton is located on the Planck brane. In this model gravitons can propagate in the extra dimension, leading to a Kaluza-Klein tower of states which can be detected as massive spin-2 resonances that couple to all SM particles. The resonance with the lowest mass is known as the RS graviton G. The model has two parameters: the graviton mass mG∗ , and the dimensionless coupling κ/M̃pl, where κ is the curvature of the warped fifth dimension and M̃pl = Mpl/ √ 8π is the reduced Planck mass. The RS1 model introduces higher-dimensional operators that give excessively large contributions to flavour changing neutral current (FCNC) processes and to observables related to SM electroweak precision tests. An extension of the RS1 model, the bulk RS model, has been proposed to address this issue. In this model, the SM fields are also allowed to propagate in the extra dimension: the first and second generation fermions are chosen to be localized near the Planck brane, while the top-quark and the Higgs boson are localized near the TeV brane to account for the large top-quark Yukawa coupling. In this scenario, FCNCs and contributions to electroweak observables from higher-dimensional operators are suppressed, the graviton (here denoted by G∗bulk) production and decay via light fermion channels is highly suppressed, the probability for the graviton to decay into photons is negligible, and the coupling to heavy particles, such as top-quark, W , Z and Higgs bosons is strongly enhanced. In this model the branching ratio of G∗bulk →WW is about 15%. Direct searches for a heavy WW resonance have been performed by the CDF and D0 collaborations at the Tevatron. The D0 collaboration explored diboson resonant production using the lνlν and lνjj final states [11]; these searches excluded an RS graviton with a mass between 300 GeV and 754 GeV, assuming κ/M̃pl = 0.1. The CDF collaboration also searched for resonant WW production in the eνjj final state, resulting in a lower limit of 607 GeV on the mass of an RS graviton [12], assuming the same coupling strength κ/M̃pl = 0.1. No previous work on searches for G ∗ bulk has been published. The ATLAS detector [13] is a multi-purpose particle physics detector with forward-backward symmetric cylindrical geometry [14]. The inner tracking detector (ID) covers the region |η| < 2.5, and consists of a silicon pixel detector, a silicon microstrip detector, and a straw tube tracker with transition radiation detection capability. The ID is surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field. A highgranularity lead/liquid-argon (LAr) sampling calorimeter measures the energy and the position of electromagnetic showers with |η| < 3.2. LAr sampling calorimeters are also used to measure hadronic showers in the endcap (1.5 < |η| < 3.2) and forward (3.1 < |η| < 4.9) regions, while an iron/scintillator tile calorimeter measures hadronic showers in the central region (|η| < 1.7). The muon spectrometer (MS) surrounds the calorimeters and consists of three large superconducting air-core toroids, each with eight coils, a system of precision tracking chambers (|η| < 2.7), and fast tracking chambers for triggering. A three-level trigger system selects events to be recorded for offline analysis.

Search for new phenomena in the WW -> vertical bar v vertical bar ' v ' final state in pp collisions at root s=7 TeV with the ATLAS detector

This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb−1. WW → lνlν ′ (l, l = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. Search for new phenomena in the WW → lνlν final state in pp collisions at √ s = 7 TeV with the ATLAS detector The ATLAS Collaboration (Dated: May 2, 2014) This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at √ s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb. WW → lνl′ν′ (l, l′ = e or μ) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively. PACS numbers: 14.70.Kv, 04.60.Kz, 12.60.Cn The existence of new phenomena can be probed by studying heavy gauge boson pair production. Heavy particles that can decay to gauge boson pairs are predicted in many scenarios of physics beyond the Standard Model (SM), including the Extended Gauge Model (EGM) [1], Extra Dimensions [2–6], and Technicolor models [7–9]. This paper describes a search for resonant WW production in the WW → lνlν (l, l = e or μ) decay channel using a data sample corresponding to an integrated luminosity of 4.7 fb, collected by the ATLAS detector during 2011 at a center-of-mass energy of 7 TeV. A spin2 Randall-Sundrum (RS) graviton model [2] and one of its extensions, the bulk RS graviton model [10], are used as benchmarks to interpret the analysis result. The original RS model (RS1) was proposed to solve the hierarchy problem. It postulates a warped 5-dimensional universe, where the SM particles are localized on the TeV brane and the graviton is located on the Planck brane. In this model gravitons can propagate in the extra dimension, leading to a Kaluza-Klein tower of states which can be detected as massive spin-2 resonances that couple to all SM particles. The resonance with the lowest mass is known as the RS graviton G. The model has two parameters: the graviton mass mG∗ , and the dimensionless coupling κ/M̃pl, where κ is the curvature of the warped fifth dimension and M̃pl = Mpl/ √ 8π is the reduced Planck mass. The RS1 model introduces higher-dimensional operators that give excessively large contributions to flavour changing neutral current (FCNC) processes and to observables related to SM electroweak precision tests. An extension of the RS1 model, the bulk RS model, has been proposed to address this issue. In this model, the SM fields are also allowed to propagate in the extra dimension: the first and second generation fermions are chosen to be localized near the Planck brane, while the top-quark and the Higgs boson are localized near the TeV brane to account for the large top-quark Yukawa coupling. In this scenario, FCNCs and contributions to electroweak observables from higher-dimensional operators are suppressed, the graviton (here denoted by G∗bulk) production and decay via light fermion channels is highly suppressed, the probability for the graviton to decay into photons is negligible, and the coupling to heavy particles, such as top-quark, W , Z and Higgs bosons is strongly enhanced. In this model the branching ratio of G∗bulk →WW is about 15%. Direct searches for a heavy WW resonance have been performed by the CDF and D0 collaborations at the Tevatron. The D0 collaboration explored diboson resonant production using the lνlν and lνjj final states [11]; these searches excluded an RS graviton with a mass between 300 GeV and 754 GeV, assuming κ/M̃pl = 0.1. The CDF collaboration also searched for resonant WW production in the eνjj final state, resulting in a lower limit of 607 GeV on the mass of an RS graviton [12], assuming the same coupling strength κ/M̃pl = 0.1. No previous work on searches for G ∗ bulk has been published. The ATLAS detector [13] is a multi-purpose particle physics detector with forward-backward symmetric cylindrical geometry [14]. The inner tracking detector (ID) covers the region |η| < 2.5, and consists of a silicon pixel detector, a silicon microstrip detector, and a straw tube tracker with transition radiation detection capability. The ID is surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field. A highgranularity lead/liquid-argon (LAr) sampling calorimeter measures the energy and the position of electromagnetic showers with |η| < 3.2. LAr sampling calorimeters are also used to measure hadronic showers in the endcap (1.5 < |η| < 3.2) and forward (3.1 < |η| < 4.9) regions, while an iron/scintillator tile calorimeter measures hadronic showers in the central region (|η| < 1.7). The muon spectrometer (MS) surrounds the calorimeters and consists of three large superconducting air-core toroids, each with eight coils, a system of precision tracking chambers (|η| < 2.7), and fast tracking chambers for triggering. A three-level trigger system selects events to be recorded for offline analysis.

Search for the Standard Model Higgs boson in the decay channel H→ZZ(*)→4ℓ with 4.8 fb-1of pp collision data at √s=7 TeV with ATLAS

This Letter presents a search for the Standard Model Higgs boson in the decay channel H → ZZ → lll ′+l ′ −, where l, l ′ = e or μ, using proton-proton collisions at √ s = 7 TeV recorded with the ATLAS detector and corresponding to an integrated luminosity of 4.8 fb. The four-lepton invariant mass distribution is compared with Standard Model background expectations to derive upper limits on the cross section of a Standard Model Higgs boson with a mass between 110 GeV and 600 GeV. The mass ranges 134−156 GeV, 182−233 GeV, 256−265 GeV and 268−415 GeV are excluded at the 95% confidence level. The largest upward deviations from the background-only hypothesis are observed for Higgs boson masses of 125 GeV, 244 GeV and 500 GeV with local significances of 2.1, 2.2 and 2.1 standard deviations, respectively. Once the look-elsewhere effect is considered, none of these excesses are significant.

Measurement of the W→τντcross section in pp collisions at s=7 TeV with the ATLAS experiment

The cross section for the production of W bosons with subsequent decay W → τντ is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of √ s = 7 TeV and corresponds to an integrated luminosity of 34 pb. The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W → τντ branching ratio is measured to be σ W→τντ = 11.1± 0.3 (stat)± 1.7 (syst)± 0.4 (lumi) nb.The cross section for the production of W bosons with subsequent decay W→τν_τ is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton–proton center-of-mass energy of √s = 7TeV and corresponds to an integrated luminosity of 34 pb^(−1). The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W→τν_τ branching ratio is measured to be σ^(tot) _(W→τντ) = 11.1±0.3 (stat)±1.7 (syst)±0.4 (lumi) nb.

Search for diphoton events with large missing transverse momentum in 1 fb-1of 7 TeV proton-proton collision data with the ATLAS detector

CERN-PH-EP-2011-160 A search for diphoton events with large missing transverse momentum has been performed using 1.07 fb of protonproton collision data at √ s = 7TeV recorded with the ATLAS detector. No excess of events was observed above the Standard Model prediction and 95% Confidence Level (CL) upper limits are set on the production cross section for new physics. The limits depend on each model parameter space and vary as follows: σ < (22 − 129) fb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, σ < (27−91) fb in the context of a minimal model of gauge-mediated supersymmetry breaking (SPS8), and σ < (15−27) fb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 805GeV, for bino masses above 50GeV, is set on the GGM gluino mass. Lower limits of 145TeV and 1.23TeV are set on the SPS8 breaking scale Λ and on the UED compactification scale 1/R, respectively. These limits provide the most stringent tests of these models to date.

Search for the Higgs boson in the H -> WW -> lvjj decay channel at root s=7 TeV with the ATLAS detector

A search for the Standard Model Higgs boson has been performed in the H -> WW -> lvjj channel using 4.7 fb(-1) of pp collision data recorded at a centre-of-mass energy of root s = 7 TeV with the ATLAS detector at the Large Hadron Collider. Higgs boson candidates produced in association with zero, one or two jets are included in the analysis to maximize the acceptance for both gluon fusion and weak boson fusion Higgs boson production processes. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 300 GeV WW produced in association with zero or one jet is 2.2 pb (1.9 pb), corresponding to 1.9 (1.6) times the Standard Model prediction. In the Higgs boson plus two jets channel, which is more sensitive to the weak boson fusion process, the observed (expected) 95% confidence level upper bound on the cross section for H -> WW production with m(H) = 400 GeV is 0.7 pb (0.6 pb), corresponding to 7.9 (6.5) times the Standard Model prediction