A search for the Standard Model Higgs boson in proton–proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 ...fb−1 collected at s=7 TeV in 2011 and 5.8 fb−1 at s=8 TeV in 2012. Individual searches in the channels H→ZZ(⁎)→4ℓ, H→γγ and H→WW(⁎)→eνμν in the 8 TeV data are combined with previously published results of searches for H→ZZ(⁎), WW(⁎), bb¯ and τ+τ− in the 7 TeV data and results from improved analyses of the H→ZZ(⁎)→4ℓ and H→γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of 126.0±0.4(stat)±0.4(sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10−9, is compatible with the production and decay of the Standard Model Higgs boson.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The luminosity calibration for the ATLAS detector at the LHC during pp collisions at ... in 2010 and 2011 is presented. ...Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at ... A luminosity uncertainty of ... is obtained for the 47 pb^sup -1^ of data delivered to ATLAS in 2010, and an uncertainty of ... is obtained for the 5.5 fb^sup -1^ delivered in 2011.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in ...proton-proton collision data at a centre-of-mass energy of ... corresponding to an integrated luminosity of 38 pb^sup -1^. Jets are reconstructed with the anti-k ^sub t^ algorithm with distance parameters R=0.4 or R=0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta p ^sub T^greater than or equal to20 GeV and pseudorapidities |eta|<4.5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2.5 % in the central calorimeter region (|eta|<0.8) for jets with 60less than or equal top ^sub T^<800 GeV, and is maximally 14 % for p ^sub T^<30 GeV in the most forward region 3.2less than or equal to|eta|<4.5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon p ^sub T^, the sum of the transverse momenta of tracks associated to the jet, or a system of low-p ^sub T^ jets recoiling against a high-p ^sub T^ jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-p ^sub T^ jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb−1 to 4.9 fb−1 of pp collisions collected ...at s=7 TeV is presented. The Higgs boson mass ranges 112.9–115.5 GeV, 131–238 GeV and 251–466 GeV are excluded at the 95% confidence level (CL), while the range 124–519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around mH∼126 GeV with a local significance of 3.5 standard deviations (σ). The local significances of H→γγ, H→ZZ(⁎)→ℓ+ℓ−ℓ′+ℓ′− and H→WW(⁎)→ℓ+νℓ′−ν¯, the three most sensitive channels in this mass range, are 2.8σ, 2.1σ and 1.4σ, respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110–600 GeV is estimated to be ∼1.4% or, equivalently, 2.2σ.
Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead–lead collisions at sNN=2.76 TeV ...corresponding to an integrated luminosity of approximately 7 μb−1, ATLAS has measured jets with a calorimeter system over the pseudorapidity interval |η|<2.1 and over the transverse momentum range 38<pT<210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R=0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet “central-to-peripheral ratio,” RCP. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. RCP varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.
This Letter describes the measurement of elliptic flow of charged particles in lead–lead collisions at sNN=2.76 TeV using the ATLAS detector at the Large Hadron Collider (LHC). The results are based ...on an integrated luminosity of approximately 7 μb−1. Elliptic flow is measured over a wide region in pseudorapidity, |η|<2.5, and over a broad range in transverse momentum, 0.5<pT<20 GeV. The elliptic flow parameter v2 is obtained by correlating individual tracks with the event plane measured using energy deposited in the forward calorimeters. As a function of transverse momentum, v2(pT) reaches a maximum at pT of about 3 GeV, then decreases and becomes weakly dependent on pT above 7–8 GeV. Over the measured pseudorapidity region, v2 is found to be only weakly dependent on η, with less variation than observed at lower beam energies. The results are discussed in the context of previous measurements at lower collision energies, as well as recent results from the LHC.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton ...collisions at ... The sample corresponds to an integrated luminosity of 35 pb^sup -1^. Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within |y|<2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Detailed measurements of the electron performance of the ATLAS detector at the LHC are reported, using decays of the
Z
,
W
and
J
/
ψ
particles. Data collected in 2010 at
are used, corresponding to an ...integrated luminosity of almost 40 pb
−1
. The inter-alignment of the inner detector and the electromagnetic calorimeter, the determination of the electron energy scale and resolution, and the performance in terms of response uniformity and linearity are discussed. The electron identification, reconstruction and trigger efficiencies, as well as the charge misidentification probability, are also presented.
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