-
The ATLAS Collaboration,
G. Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz, [......],
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: First measurements of the W → ℓν and Z/γ
*
→ ℓℓ (ℓ = e, μ) production cross sections in proton-proton collisions at
Ös = 7\textTeV \sqrt {s} = 7\;{\text{TeV}} are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ℓν and 179 Z/γ
* → ℓℓ candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb. The measured
total W and Z/γ
∗-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels
are
sW\texttot \sigma_W^{\text{tot}} . BR(W → ℓν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and
sZ /
g \texttot \sigma_{{{Z} \left/ {\gamma } \right.}}^{\text{tot}} BR(Z/γ
∗ → ℓℓ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09(lumi) nb (within the invariant mass window 66 < m
ℓℓ
< 116GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W
+ and W
− production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations
are found to agree with the measurements.
KeywordsHadron-Hadron Scattering
Journal of High Energy Physics 04/2012; 2010(12):1-65. · 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, [......],
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 the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7TeV
is reported, based on a total integrated luminosity of up to 40pb−1 collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H→γγ, H→ZZ
(∗)→ℓℓℓℓ, H→ZZ→ℓℓνν, H→ZZ→ℓℓqq, H→WW
(∗)→ℓνℓν and H→WW→ℓνqq (ℓis e, μ) are combined in a mass range from 110GeV to 600GeV. The highest sensitivity is achieved in the mass range between 160GeV
and 170GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard
Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of
heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95%
CL for a Higgs boson mass in the range from 140 GeVto 185GeV.
European Physical Journal C 04/2012; 71(9):1-30. · 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. 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 measurement of the production cross-section for top quark pairs (t[`(t)]t\bar{t}) in pp collisions at Ös=7TeV\sqrt{s}=7\ \ \mbox{TeV} is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different
topologies: single lepton (electron e or muon μ) with large missing transverse energy and at least four jets, and dilepton (ee, μμ or eμ) with large missing transverse energy and at least two jets. In a data sample of 2.9pb−1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding
expected backgrounds from non-t[`(t)]t\bar{t} Standard Model processes are estimated using data-driven methods and determined to be 12.2±3.9 events and 2.5±0.6 events,
respectively. The kinematic properties of the selected events are consistent with SM t[`(t)]t\bar{t} production. The inclusive top quark pair production cross-section is measured to be
st[`(t)]=145±31(stat.) +42-27(syst.)pb.\sigma_{t\bar{t}}=145\pm31(\mathrm{stat.}) {}^{+42}_{-27}(\mathrm {syst.})\ \mbox{pb}.
The measurement agrees with perturbative QCD calculations.
European Physical Journal C 04/2012; 71(3):1-36. · 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, [......],
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: Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7TeV using
the ATLAS detector. The measurement uses an integrated luminosity of 17nb−1 recorded at the Large Hadron Collider. The anti-k
t
algorithm is used to identify jets, with two jet resolution parameters, R=0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets
above 60GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse
momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variableχ. The results are compared to expectations based on next-to-leading-order QCD, which agree with the data, providing a validation
of the theory in a new kinematic regime.
European Physical Journal C 04/2012; 71(2):1-59. · 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 ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a
2T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC
beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking
performance has been measured with 7.6million cosmic-ray events, collected using a tracking trigger and reconstructed with
modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close
to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation
turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry.
After the initial alignment, a transverse impact parameter resolution of 22.1±0.9μm and a relative momentum resolution σ
p
/p=(4.83±0.16)×10−4 GeV−1×p
T have been measured for high momentum tracks.
European Physical Journal C 04/2012; 70(3):787-821. · 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 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
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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
