Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at sqrt(S(NN) ) = 2.76 TeV with the ATLAS Detector at the LHC

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.Lett. 105 (2010) 252303, 2010.
Inspire Record 878733 DOI 10.17182/hepdata.63790

Using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally-segmented electromagnetic and hadronic calorimeters. The underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

4 data tables

Asymmetry in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.

Asymmetry in 7 TeV P-P collisions.

DeltaPhi distribution in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.

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Measurement of the production cross section for W-bosons in association with jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Lett.B 698 (2011) 325-345, 2011.
Inspire Record 882534 DOI 10.17182/hepdata.57048

This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma(W+ \ge n) / sigma(W+ \ge n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n \le 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.

8 data tables

The measured cross section times branching ratio for W+jets in the electron channel as a function of corrected jet multiplicity.

The measured cross section times branching ratio for W+jets in the muon channel as a function of corrected jet multiplicity.

The measured cross section ratio for W+jets in the electron channel as a function of corrected jet multiplicity.

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Measurement of underlying event characteristics using charged particles in pp collisions at $\sqrt{s} = 900 GeV$ and 7 TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.D 83 (2011) 112001, 2011.
Inspire Record 879407 DOI 10.17182/hepdata.57151

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The 'underlying event' is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest-pt charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, pt density, and average pt are measured. The data show a higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data.

22 data tables

Particle Number Density versus Lead Particle PT at centre-of-mass energy 900 GeV.

Particle Number Density versus Lead Particle PT at centre-of-mass energy 7000 GeV.

Particle PT Density versus Lead Particle PT at centre-of-mass energy 900 GeV.

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Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Eur.Phys.J.C 71 (2011) 1846, 2011.
Inspire Record 930220 DOI 10.17182/hepdata.58001

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.

10 data tables

Inclusive double differential b-jet cross section as a function of PT for the |rapidity| range 0.0-0.3 from the lifetime-based analysis.

Inclusive double differential b-jet cross section as a function of PT for the |rapidity| range 0.3-0.8 from the lifetime-based analysis.

Inclusive double differential b-jet cross section as a function of PT for the |rapidity| range 0.8-1.2 from the lifetime-based analysis.

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Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in sqrt{s} = 7 TeV pp

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.Lett. 106 (2011) 131802, 2011.
Inspire Record 889431 DOI 10.17182/hepdata.57900

This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from sqrt{s} = 7 TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb-1. No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. For A_0 = 0 GeV, tan beta = 3, mu > 0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.

4 data tables

Distribution of ET(C=MISSING) IN GEV for data and background MC calculation.

Distribution of MT IN GEV for data and background MC calculation.

Distribution of M(C=EFFECTIVE) IN GEV for data and background MC calculation.

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Measurement of Dijet Azimuthal Decorrelations in pp Collisions at sqrt(s)=7 TeV

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.Lett. 106 (2011) 172002, 2011.
Inspire Record 889546 DOI 10.17182/hepdata.58478

Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full dataset (L=36/pb) acquired by the ATLAS detector during the 2010 sqrt(s)=7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high energy regime.

9 data tables

Distribution for the maxPT jet (P=3) from 110 to 160 GeV.

Distribution for the maxPT jet (P=3) from 160 to 210 GeV.

Distribution for the maxPT jet (P=3) from 210 to 260 GeV.

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Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Lett.B 701 (2011) 186-203, 2011.
Inspire Record 890749 DOI 10.17182/hepdata.57597

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded by the ATLAS experiment in sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 35 inverse picobarns of analysed data. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tan(beta)= 3, A_0=0 and mu>0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date.

6 data tables

The distribution in Meff (scalar sum of the missing transverse momentum and the transverse momenta of the two highest pT jets) for events with at least 2 jets after the application of all selection criteria (other than the Meff cut itself). The table shows the number of observed data points per 100 GeV bin plus the background prediction of the Standard-Model Monte-Carlo and its upper and lower 1-sigma error limits uncertainty band.

The distribution in Meff (scalar sum of the missing transverse momentum and the transverse momenta of the three highest pT jets) for events with at least 3 jets after the application of all selection criteria (other than the Meff cut itself). The table shows the number of observed data points per 100 GeV bin plus the background prediction of the Standard-Model Monte-Carlo and its upper and lower 1-sigma uncertainty band error limits.

The distribution in MT2 for events with at least 2 jets after the application of all selection criteria (other than the MT2 cut itself). The table shows the number of observed data points per 40 GeV bin plus the background prediction of the Standard-Model Monte-Carlo and its upper and lower 1-sigma uncertainty band error limits.

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Search for supersymmetry in pp collisions at sqrt{s} = 7TeV in final states with missing transverse momentum and b-jets

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Lett.B 701 (2011) 398-416, 2011.
Inspire Record 893493 DOI 10.17182/hepdata.57742

Results are presented of a search for supersymmetric particles in events with large missing transverse momentum and at least one heavy flavour jet candidate in sqrt{s} = 7 TeV proton-proton collisions. In a data sample corresponding to an integrated luminosity of 35 pb-1 recorded by the ATLAS experiment at the Large Hadron Collider, no significant excess is observed with respect to the prediction for Standard Model processes. For R-parity conserving models in which sbottoms (stops) are the only squarks to appear in the gluino decay cascade, gluino masses below 590 GeV (520 GeV) are excluded at the 95% C.L. The results are also interpreted in an MSUGRA/CMSSM supersymmetry breaking scenario with tan(beta)=40 and in an SO(10) model framework.

14 data tables

Distribution of the effective mass for data and the SM expectation in the zero-lepton plus 3 jet channel.

Distribution of the missing ET for data and the SM expectation in the zero-lepton plus 3 jet channel.

Distribution of the effective mass for data and the SM expectation in the one-lepton plus 2 jet channel.

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Search for a heavy particle decaying into an electron and a muon with the ATLAS detector in sqrt(s) = 7 TeV pp collisions at the LHC

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.Lett. 106 (2011) 251801, 2011.
Inspire Record 894358 DOI 10.17182/hepdata.57150

This Letter presents the first search for a heavy particle decaying into an e\mu final state in sqrt(s)=7 TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35/pb. No excess above the Standard Model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming single coupling dominance and the couplings lambda'_{311}=0.11, lambda_{312}=0.07. In a lepton flavor violating model, a Z'-like vector boson with masses of 0.70 to 1.00 TeV and corresponding cross sections times branching ratios of 0.175 to 0.183 pb is excluded. These results extend to higher mass RPV sneutrinos and LFV Z's than previous constraints from the Tevatron.

4 data tables

Observed e-mu invariant mass distribution.

The observed 95% CL upper limits on the cross section for p p --> sneutrino x BR(sneutrino -> e-mu) as a function of the sneutrino mass.

The 95% CL upper limits on the Lambda311 coupling as a function of the sneutrino mass, for threee values of Lambda312.

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Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Lett.B 701 (2011) 1-19, 2011.
Inspire Record 892044 DOI 10.17182/hepdata.58184

Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this paper a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton-proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb-1. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.

6 data tables

Distribution of the observed rate of energy loss in the Pixel detector plus the simulated background and model estimates for three gluino masses.

Distribution of the observed BETA values in the Tile Calorimeter plus the simulated background and model estimates for three gluino masses.

Distribution of the heavy particle Mass estimated from the Pixel detector data plus the simulated background and model estimates for three gluino masses. A cut of dE/dx > 1.1 MeV/(gm*cm**2) is imposed.;.

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