-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
X. Zhuang,
V. Zhuravlov,
R. Zimmermann,
S. Zimmermann,
M. Ziolkowski,
L. Živković,
G. Zobernig,
A. Zoccoli,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009.
These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers,
their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in
the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution
and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency
and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer
is ready to detect muons produced in high energy proton–proton collisions.
European Physical Journal C 04/2012; 70(3):875-916. · 3.63 Impact Factor
-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
X. Zhuang,
V. Zhuravlov,
R. Zimmermann,
S. Zimmermann,
M. Ziolkowski,
L. Živković,
G. Zobernig,
A. Zoccoli,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation
in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector has successfully
collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter
performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector
operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation
of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems’ precision
is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.
European Physical Journal C 04/2012; 70(4):1193-1236. · 3.63 Impact Factor
-
The ATLAS collaboration,
G. Aad,
E. Abat,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins, [......],
M. Ziolkowski,
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009
at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS
detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track-and
calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful
running at higher energies.
KeywordsHadron-Hadron Scattering
Journal of High Energy Physics 04/2012; 2010(9):1-66. · 5.83 Impact Factor
-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
X. Zhuang,
V. Zhuravlov,
R. Zimmermann,
S. Zimmermann,
M. Ziolkowski,
L. Živković,
G. Zobernig,
A. Zoccoli,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for large-scale production of
events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions,
through packages simulating the response of the various detectors and triggers. All of these components come together under
the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector
description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors.
Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output
against known physics processes.
European Physical Journal C 04/2012; 70(3):823-874. · 3.63 Impact Factor
-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
R. Zimmermann,
S. Zimmermann,
M. Ziolkowski,
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter
was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation
for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random
triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing performance,
electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events
allow to check the intrinsic constant term of the energy resolution. The uniformity of the electromagnetic barrel calorimeter
response along η (averaged overφ) is measured at the percent level using minimum ionizing cosmic muons. Finally, studies of electromagnetic showers from radiative
muons have been used to cross-check the Monte Carlo simulation. The performance results obtained using the ATLAS readout,
data acquisition, and reconstruction software indicate that the liquid argon calorimeter is well-prepared for collisions at
the dawn of the LHC era.
European Physical Journal C 04/2012; 70(3):723-753. · 3.63 Impact Factor
-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
R. Zimmermann,
S. Zimmermann,
M. Ziolkowski,
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
M. zur Nedden,
V. Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons.
In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter
gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the
second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated
contribution to the constant term of (0.29+0.05-0.04)(0.29^{+0.05}_{-0.04})% in the barrel and (0.54+0.06-0.04)(0.54^{+0.06}_{-0.04})% in the endcaps. The same data are used to measure the drift velocity of ionization electrons in liquid argon, which is found
to be 4.61±0.07mm/μs at 88.5K and 1kV/mm.
European Physical Journal C 04/2012; 70(3):755-785. · 3.63 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
O S AbouZeid,
H Abramowicz, [......],
R Zitoun,
L Živković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: The χ(b)(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider at sqrt[s] = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb(-1), these states are reconstructed through their radiative decays to Υ(1S,2S) with Υ → μ+ μ-. In addition to the mass peaks corresponding to the decay modes χ(b)(1P,2P) → Υ(1S)γ, a new structure centered at a mass of 10.530 ± 0.005(stat) ± 0.009(syst) GeV is also observed, in both the Υ(1S)γ and Υ(2S)γ decay modes. This structure is interpreted as the χ(b)(3P) system.
Physical Review Letters 04/2012; 108(15):152001. · 7.37 Impact Factor
-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at Ös = 7\sqrt{s} = 7TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having
different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from
these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0<μ<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%,
dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods
differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with
the PYTHIA and PHOJET event generators and the ATLAS detector simulation.
European Physical Journal C 04/2012; 71(4):1-37. · 3.63 Impact Factor
-
G. ATLAS Collaboration Aad,
B. Abbott,
J. Abdallah,
S. Abdel Khalek,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
O. S. AbouZeid, [......],
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: This Letter presents a search for the Standard Model Higgs boson in the
decay channel
H→ZZ→ℓ+ℓ-ℓℓ,
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-1. 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.
Physics Letters B 03/2012; 710:383-402. · 3.95 Impact Factor
-
G. ATLAS Collaboration Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz,
H. Abreu, [......],
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS experiment at the LHC has measured the centrality dependence
of charged particle pseudorapidity distributions over |η|<2 in
lead-lead collisions at a nucleon-nucleon centre-of-mass
energy of sNN=2.76 TeV. In order to include particles with
transverse momentum as low as 30 MeV, the data were recorded with the
central solenoid magnet off. Charged particles were reconstructed with
two algorithms (2-point "tracklets" and full tracks) using information
from the pixel detector only. The lead-lead collision centrality
was characterized by the total transverse energy in the forward
calorimeter in the range 3.2<|η|<4.9. Measurements are
presented of the per-event charged particle pseudorapidity distribution,
dNch/dη, and the average charged particle multiplicity in
the pseudorapidity interval |η|<0.5 in several intervals of
collision centrality. The results are compared to previous mid-rapidity
measurements at the LHC and RHIC. The variation of the mid-rapidity
charged particle yield per colliding nucleon pair with the number of
participants is consistent with lower sNN results. The shape
of the dNch/dη distribution is found to be independent of
centrality within the systematic uncertainties of the measurement.
Physics Letters B 03/2012; 710:363-382. · 3.95 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for the Higgs boson has been performed in the H→WW(*)→ℓ(+)νℓ(-)ν[over ¯] channel (ℓ=e/μ) with an integrated luminosity of 2.05 fb(-1) of pp collisions at √s=7 TeV collected with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 110 GeV<m(H)<300 GeV. The observations exclude the presence of a standard model Higgs boson with a mass 145<m(H)<206 GeV at 95% confidence level.
Physical Review Letters 03/2012; 108(11):111802. · 7.37 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
O S Abouzeid, [......],
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s=7 TeV. In the diphoton mass range 110-150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110-150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113-115 GeV and 134.5-136 GeV.
Physical Review Letters 03/2012; 108(11):111803. · 7.37 Impact Factor
-
G. ATLAS Collaboration Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz,
H. Abreu, [......],
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for squarks and gluinos in events containing jets, missing
transverse momentum and no electrons or muons is presented. The data
were recorded in 2011 by the ATLAS experiment in s=7 TeV
proton-proton collisions at the Large Hadron Collider. No excess
above the Standard Model background expectation is observed in
1.04 fb of data. Gluino and squark masses below 700 GeV
and 875 GeV respectively 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 limit increases
to 1075 GeV for squarks and gluinos of equal mass. In MSUGRA/CMSSM
models with tanβ=10, A0=0 and μ>0, squarks and
gluinos of equal mass are excluded for masses below 950 GeV. These
limits extend the region of supersymmetric parameter space excluded by
previous measurements.
Physics Letters B 02/2012; 710:67-85. · 3.95 Impact Factor
-
G. ATLAS Collaboration Aad,
B. Abbott,
J. Abdallah,
S. Abdel Khalek,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
O. S. AbouZeid, [......],
M. Ziolkowski,
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: 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-ℓℓ
and
H→WW→ℓ+νℓν¯,
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.
Physics Letters B 02/2012; 710:49-66. · 3.95 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb(-1) of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of 420 GeV and a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, top-partner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.
Physical Review Letters 01/2012; 108(4):041805. · 7.37 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the ZZ production cross section in proton-proton collisions at sqrt[s] = 7 TeV using data corresponding to an integrated luminosity of 1.02 fb(-1) recorded by the ATLAS experiment at the LHC is presented. Twelve events containing two Z boson candidates decaying to electrons and/or muons are observed, with an expected background of 0.3 ± 0.3(stat)(-0.3)(+0.4)(syst) events. The cross section measured in a phase-space region with good detector acceptance and for dilepton masses within the range 66 to 116 GeV is σ(ZZ → ℓ+ ℓ- ℓ+ ℓ-)(fid) = 19.4(-5.2)(+6.3)(stat)(-0.7)(+0.9)(syst) ± 0.7(lumi) fb. The resulting total cross section for on-shell ZZ production, σ(ZZ)(tot) = 8.5(-2.3)(+2.7)(stat)(-0.3)(+0.4)(syst) ± 0.3(lumi) pb, is consistent with the standard model expectation of 6.5(-0.2)(+0.3) pb calculated at the next-to-leading order in QCD. Limits on anomalous neutral triple gauge boson couplings are derived.
Physical Review Letters 01/2012; 108(4):041804. · 7.37 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at √s=7 TeV at the Large Hadron Collider and correspond to a total integrated luminosity of 1.08 (1.21) fb(-1) in the e(+)e(-) (μ(+)μ(-)) channel. No statistically significant excess above the standard model expectation is observed and upper limits are set at the 95% C.L. on the cross section times branching fraction of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the sequential standard model Z' boson is set. A Randall-Sundrum graviton with coupling k/M(Pl)=0.1 is excluded at 95% C.L. for masses below 1.63 TeV.
Physical Review Letters 12/2011; 107(27):272002. · 7.37 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Živković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for a Higgs boson has been performed in the H→WW→ℓνjj channel in 1.04 fb(-1) of pp collision data at √s=7 TeV recorded with the ATLAS detector at the Large Hadron Collider. 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 240 GeV<m(H)<600 GeV. The best sensitivity is reached for m(H)=400 GeV, where the 95% confidence level upper bound on the cross section for H→WW production is 3.1 pb, or 2.7 times the standard model prediction.
Physical Review Letters 12/2011; 107(23):231801. · 7.37 Impact Factor
-
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz,
H. Abreu, [......],
R. Zitoun,
L. Živković,
V. V. Zmouchko,
G. Zobernig,
A. Zoccoli,
Y. Zolnierowski,
A. Zsenei,
M. zur Nedden,
V. Zutshi,
L. Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: 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< p T<400 GeV and rapidity in the range |
y|<2.1. The boverline{b}-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 χ 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 boverline{b}-dijet cross-section. However,
it does not reproduce the measured inclusive cross-section well,
particularly for central b-jets with large transverse momenta.
European Physical Journal C 11/2011; 71:1846. · 3.63 Impact Factor
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
R Zitoun,
L Živković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for a heavy standard model Higgs boson decaying via H→ZZ→→ℓ(+)ℓ(-)νν, where ℓ=e, μ, is presented. It is based on proton-proton collision data at √s=7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340<m(H)<450 GeV at the 95% confidence level.
Physical Review Letters 11/2011; 107(22):221802. · 7.37 Impact Factor
