-
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
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G. Aad,
E. Abat,
J Abdallah,
AA Abdelalim,
A. Abdesselam,
O. Abdinov,
BA Abi,
M Abolins, H Abramowicz,
E. Acerbi, [......],
G. Barbier,
P. Barclay,
DY Bardin,
P Bargassa,
T Barillari,
M. Barisonzi,
BM Barnett,
RM Barnett,
S Baron,
A Baroncelli
-
G. Aad,
E. Abat,
J Abdallah,
AA Abdelalim,
A. Abdesselam,
O. Abdinov,
BA Abi,
M Abolins, H Abramowicz,
E. Acerbi, [......],
G. Barbier,
P. Barclay,
DY Bardin,
P Bargassa,
T Barillari,
M. Barisonzi,
BM Barnett,
RM Barnett,
S Baron,
A Baroncelli
-
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
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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
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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, [......],
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
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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
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H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
C. Alexa,
V. Andreev,
S. Antonelli,
P. Antonioli,
A. Antonov, [......],
W. Zeuner,
Z. Zhang,
B. O. Zhautykov,
N. Zhmak,
A. Zichichi,
R. Žlebčík,
H. Zohrabyan,
Z. Zolkapli,
F. Zomer,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Measurements of open charm production cross sections in deep-inelastic ep
scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced
cross sections sigma_red^{c\bar{c}} for charm production are obtained in the
kinematic range of photon virtuality 2.5<Q2<2000 GeV2 and Bjorken scaling
variable 0.00003<x<0.05. The combination method accounts for the correlations
of the systematic uncertainties among the different data sets. The combined
charm data together with the combined inclusive deep-inelastic scattering cross
sections from HERA are used as input for a detailed NLO QCD analysis to study
the influence of different heavy flavour schemes on the parton distribution
functions. The optimal values of the charm mass as a parameter in these
different schemes are obtained. The implications on the NLO predictions for
W^{\pm} and Z production cross sections at the LHC are investigated. Using the
fixed flavour number scheme, the running mass of the charm quark is determined.
11/2012;
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ZEUS collaboration, H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
O. Zabiegalov,
A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: The production of Z0 bosons in the reaction ep -> eZ0p*, where p* stands for
a proton or a low-mass nucleon resonance, has been studied in ep collisions at
HERA using the ZEUS detector. The analysis is based on a data sample collected
between 1996 and 2007, amounting to 496 pb-1 of integrated luminosity. The Z0
was measured in the hadronic decay mode. The elasticity of the events was
ensured by a cut on eta_max < 3.0, where eta_max is the maximum pseudorapidity
of energy deposits in the calorimeter defined with respect to the proton beam
direction. A signal was observed at the Z0 mass. The cross section of the
reaction ep -> eZ0p* was measured to be sigma(ep -> eZ0p*) = 0.13 +/- 0.06
(stat.) +/- 0.01 (syst.) pb, in agreement with the Standard Model prediction of
0.16 pb. This is the first measurement of Z0 production in ep collisions.
10/2012;
-
ZEUS Collaboration, H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
-
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
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H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo,
O. Arslan, [......],
A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003–2007 using an integrated luminosity of 366 pb-1. Final states with an electron and jets or with missing transverse momentum and jets were analyzed, searching for resonances or other deviations from the standard model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498 pb-1. Limits on the Yukawa coupling, λ, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the Buchmüller-Rückl-Wyler model. Leptoquarks with a coupling λ=0.3 are excluded for masses up to 699 GeV.
Phys. Rev. D. 07/2012; 86(1).
-
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
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ZEUS Collaboration, H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
A. F. Zarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Inclusive-jet cross sections have been measured in the reaction ep->e+jet+X
for photon virtuality Q2 < 1 GeV2 and gamma-p centre-of-mass energies in the
region 142 < W(gamma-p) < 293 GeV with the ZEUS detector at HERA using an
integrated luminosity of 300 pb-1. Jets were identified using the kT, anti-kT
or SIScone jet algorithms in the laboratory frame. Single-differential cross
sections are presented as functions of the jet transverse energy, ETjet, and
pseudorapidity, etajet, for jets with ETjet > 17 GeV and -1 < etajet < 2.5. In
addition, measurements of double-differential inclusive-jet cross sections are
presented as functions of ETjet in different regions of etajet.
Next-to-leading-order QCD calculations give a good description of the
measurements, except for jets with low ETjet and high etajet. The influence of
non-perturbative effects not related to hadronisation was studied. Measurements
of the ratios of cross sections using different jet algorithms are also
presented; the measured ratios are well described by calculations including up
to O(alphas2) terms. Values of alphas(Mz) were extracted from the measurements
and the energy-scale dependence of the coupling was determined. The value of
alphas(Mz) extracted from the measurements based on the kT jet algorithm is
alphas(Mz) = 0.1206 +0.0023 -0.0022 (exp.) +0.0042 -0.0035 (th.); the results
from the anti-kT and SIScone algorithms are compatible with this value and have
a similar precision.
05/2012;
-
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
