(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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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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.
In order to study further the long-range correlations (“ridge”) observed recently in p+Pb collisions at sNN=5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v2, has ...been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 μb−1, the parameter v2 has been obtained using two- and four-particle cumulants over the pseudorapidity range |η|<2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1<η<4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb+Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p+Pb collisions. Despite the small transverse spatial extent of the p+Pb collision system, the large magnitude of v2 and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p+Pb reactions.
(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 %.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of ...s = 7 TeV has been analysed for the presence of double-parton interactions using ...data corresponding to an integrated luminosity of 36 pb super(-1), collected with the ATLAS detector at the Large Hadron Collider. The fraction of events arising from double-parton interactions, f super((D)) sub(DP), has been measured through the p sub(T) balance between the two jets and amounts to f super((D)) sub(DP) = 0.08+ or -0.01 (stat.)+ or -0.02 (sys.) for jets with transverse momentum p sub(T) > 20 GeV and rapidity |y| < 2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of sigma sub(eff) = 15+ or -3 (stat.) super(+5) sub(-3) (sys.) mb.
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