-
G. ATLAS Collaboration Aad,
B. Abbott,
J. Abdallah,
A. A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M. Abolins,
H. Abramowicz,
H. Abreu, [......],
A. M. Bach,
H. Bachacou,
K. Bachas,
G. Bachy,
M. Backes,
M. Backhaus,
E. Badescu,
P. Bagnaia,
S. Bahinipati,
Y. Bai
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
S Zimmermann,
M Ziolkowski,
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb^{-1} of integrated luminosity obtained in the 2011 LHC Pb+Pb run at sqrt[s_{NN}]=2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
Physical Review Letters 01/2013; 110(2):022301. · 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, [......],
E. Banas,
P. Banerjee,
Sw. Banerjee,
D. Banfi,
A. Bangert,
V. Bansal,
S. P. Baranov,
A. Barashkou,
T. Barber,
I. Orlov
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
S Zimmermann,
M Ziolkowski,
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum in proton-proton collisions at sqrt[s]=7 TeV are reported. Data collected by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 4.6 fb^{-1} are used. Good agreement is observed between the data and the standard model predictions. The results are translated into exclusion limits on models with large extra spatial dimensions and on pair production of weakly interacting dark matter candidates.
Physical Review Letters 01/2013; 110(1):011802. · 7.37 Impact Factor
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
S Zimmermann,
M Ziolkowski,
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: This Letter presents a search for magnetic monopoles with the ATLAS detector at the CERN Large Hadron Collider using an integrated luminosity of 2.0 fb^{-1} of pp collisions recorded at a center-of-mass energy of sqrt[s]=7 TeV. No event is found in the signal region, leading to an upper limit on the production cross section at 95% confidence level of 1.6/ϵ fb for Dirac magnetic monopoles with the minimum unit magnetic charge and with mass between 200 GeV and 1500 GeV, where ϵ is the monopole reconstruction efficiency. The efficiency ϵ is high and uniform in the fiducial region given by pseudorapidity |η|<1.37 and transverse kinetic energy 600-700<E^{kin}sinθ<1400 GeV. The minimum value of 700 GeV is for monopoles of mass 200 GeV, whereas the minimum value of 600 GeV is applicable for higher mass monopoles. Therefore, the upper limit on the production cross section at 95% confidence level is 2 fb in this fiducial region. Assuming the kinematic distributions from Drell-Yan pair production of spin-1/2 Dirac magnetic monopoles, the efficiency is in the range 1%-10%, leading to an upper limit on the cross section at 95% confidence level that varies from 145 fb to 16 fb for monopoles with mass between 200 GeV and 1200 GeV. This limit is weaker than the fiducial limit because most of these monopoles lie outside the fiducial region.
Physical Review Letters 12/2012; 109(26):261803. · 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, [......],
D Axen,
C Ay,
G Azuelos,
Y Azuma,
M A Baak,
G Baccaglioni,
C Bacci,
A M Bach,
H Bachacou,
K Bachas
-
G Aad,
B Abbott,
J Abdallah,
A A Abdelalim,
A Abdesselam,
O Abdinov,
B Abi,
M Abolins,
H Abramowicz,
H Abreu, [......],
D Axen,
C Ay,
G Azuelos,
Y Azuma,
M A Baak,
G Baccaglioni,
C Bacci,
A M Bach,
H Bachacou,
K Bachas
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
M A Baak,
G Baccaglioni,
C Bacci,
A M Bach,
H Bachacou,
K Bachas,
M Backes,
M Backhaus,
E Badescu,
P Bagnaia
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
S Zimmermann,
M Ziolkowski,
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at sqrt[s]=7 TeV. The measurement is based on 4.7 fb^{-1} of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.
Physical Review Letters 11/2012; 109(21):211803. · 7.37 Impact Factor
-
G Aad,
T Abajyan,
B Abbott,
J Abdallah,
S Abdel Khalek,
A A Abdelalim,
O Abdinov,
R Aben,
B Abi,
M Abolins, [......],
S Zimmermann,
M Ziolkowski,
R Zitoun,
L Zivković,
V V Zmouchko,
G Zobernig,
A Zoccoli,
M Zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A search for direct pair production of supersymmetric top squarks (t[over ˜]_{1}) is presented, assuming the t[over ˜]_{1} decays into a top quark and the lightest supersymmetric particle, χ[over ˜]_{1}^{0}, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5_{-3.6}^{+3.7}(4.4_{-1.3}^{+1.7}) events in two signal regions based on ∫Ldt=4.7 fb^{-1} of pp collision data taken at sqrt[s]=7 TeV with the ATLAS detector at the LHC. An exclusion region in the t[over ˜]_{1} versus χ[over ˜]_{1}^{0} mass plane is evaluated: 370<m_{t[over ˜]_{1}}<465 GeV is excluded for m_{χ[over ˜]_{1}^{0}}∼0 GeV while m_{t[over ˜]_{1}}=445 GeV is excluded for m_{χ[over ˜]_{1}^{0}}≤50 GeV.
Physical Review Letters 11/2012; 109(21):211802. · 7.37 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: This Letter presents a search for pair production of heavy down-type quarks decaying via b' → Wt in the lepton + jets channel, as b'b' → W- tW+ t → bbW+ W- W+ W- → l± νbbqqqqqq. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04 fb(-1) from pp collisions at sqrt[s] = 7 TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.
Physical Review Letters 07/2012; 109(3):032001. · 7.37 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 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 QCD analysis is reported of ATLAS data on inclusive W^{±} and Z boson production in pp collisions at the LHC, jointly with ep deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken x∼0.01. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low x. The ratio of the strange-to-down sea quark distributions is determined to be 1.00_{-0.28}^{+0.25} at absolute four-momentum transfer squared Q^{2}=1.9 GeV^{2} and x=0.023.
Physical Review Letters 07/2012; 109(1):012001. · 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: A search for pair-produced scalar particles decaying to a four-jet final state is presented. The analysis is performed using
an integrated luminosity of 34pb−1 recorded by the ATLAS detector in 2010. No deviation from the Standard Model is observed. For a scalar mass of 100GeV (190GeV)
the limit on the scalar gluon pair production cross section at 95% confidence level is 1nb (0.28nb). When these results
are interpreted as mass limits, scalar-gluons (hyperpions) with masses of 100 to 185GeV (100 to 155GeV) are excluded at
95% confidence level with the exception of a mass window of width about 5GeV (15GeV) around 140GeV.
European Physical Journal C 05/2012; 71(12):1-19. · 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 results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrt[s]=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.
Physical Review Letters 05/2012; 108(18):181802. · 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: The jet fragmentation function and transverse profile for jets with 25GeV<p
T jet<500GeV and |η
jet|<1.2 produced in proton–proton collisions with a center-of-mass energy of 7TeV are presented. The measurement is performed
using data with an integrated luminosity of 36 pb−1. Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents
are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo
event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function.
None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the
measurement.
European Physical Journal C 05/2012; 71(11):1-25. · 3.63 Impact Factor
-
The OPAL Collaboration,
G. Abbiendi,
C. Ainsley,
P. F. Åkesson,
G. Alexander,
G. Anagnostou, K. J. Anderson,
S. Asai,
D. Axen,
I. Bailey, [......],
P. S. Wells,
T. Wengler,
N. Wermes,
G. W. Wilson,
J. A. Wilson,
G. Wolf,
T. R. Wyatt,
S. Yamashita,
D. Zer-Zion,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: Hadronic event shape distributions from e+e− annihilation measured by the OPAL experiment at centre-of-mass energies between 91GeV and 209GeV are used to determine
the strong coupling α
S. The results are based on QCD predictions complete to the next-to-next-to-leading order (NNLO), and on NNLO calculations
matched to the resummed next-to-leading-log-approximation terms (NNLO + NLLA). The combined NNLO result from all variables
and centre-of-mass energies is
while the combined NNLO + NLLA result is
The completeness of the NNLO and NNLO + NLLA results with respect to missing higher order contributions, studied by varying
the renormalization scale, is improved compared to previous results based on NLO or NLO + NLLA predictions only. The observed
energy dependence of α
S agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.
European Physical Journal C 04/2012; 71(9):1-21. · 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: Results are presented of a search for particles decaying into final states with significant missing transverse momentum and
exactly two identical flavour leptons (e, μ) of opposite charge in Ös=7\sqrt{s}=7TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays
producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour
lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would
offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corresponding to an integrated
luminosity of 35pb−1 no such excess is observed. Model-independent limits are set on the contribution to these final states from supersymmetry
and are used to exclude regions of a phenomenological supersymmetric parameter space.
European Physical Journal C 04/2012; 71(7):1-18. · 3.63 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 measurement of the production cross-section for top quark pairs
(tt¯) in pp collisions at s=7 TeV is presented using data
recorded with the ATLAS detector at the Large Hadron Collider. Events
are selected in the single lepton topology by requiring an electron or
muon, large missing transverse momentum and at least three jets. With a
data sample of 35 pb-1, two different multivariate
methods, one of which uses b-quark jet identification while the other
does not, use kinematic variables to obtain cross-section measurements
of
σ=187±11(stat.)-17+18(syst.)±6(lumi.) pb
and
σ=173±17(stat.)-16+18(syst.)±6(lumi.) pb
respectively. The two measurements are in agreement with each other and
with QCD calculations. The first measurement has a better a priori
sensitivity and constitutes the main result of this Letter.
Physics Letters B 04/2012; 711:244-263. · 3.95 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: We present studies of W and Z bosons with associated high energy photons produced in pp collisions at Ös = 7 \sqrt {s} = 7 TeV. The analysis uses 35 pb−1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high p
T leptons (electrons or muons) and a photon with E
T > 15GeV separated from the lepton(s) by a distance ∆R(l, γ) > 0.7 in η-ϕ space. A total of 95 (97) pp → e
±
νγ + X(pp → μ
±
νγ + X) and 25 (23) pp → e
+
e
−
γ + X(pp → μ
+
μ
−
γ + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections
are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(αα
s
) contributions.
KeywordsHadron-Hadron Scattering
Journal of High Energy Physics 04/2012; 2011(9):1-42. · 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: Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse
momentum and exactly two isolated leptons in Ös=7TeV\sqrt {s}=7~\mbox{TeV} proton–proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical-sign or opposite-sign
electric charges are described. In a data sample corresponding to an integrated luminosity of 35pb−1 collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed
on the squark mass between 450 and 690GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric
mass hierarchy considered.
European Physical Journal C 04/2012; 71(7):1-19. · 3.63 Impact Factor
