-
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
-
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
-
V M Abazov,
B Abbott,
B S Acharya,
M Adams,
T Adams,
G D Alexeev,
G Alkhazov,
A Alton,
G Alverson,
A Askew, [......],
S W Youn,
J M Yu,
J Zennamo,
T Zhao,
T G Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
L Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the time-integrated flavor-specific semileptonic charge asymmetry in the decays of B_{s}^{0} mesons that have undergone flavor mixing, a_{sl}^{s}, using B_{s}^{0}(B[over ¯]_{s}^{0})→D_{s}^{∓}μ^{±}X decays, with D_{s}^{∓}→ϕπ^{∓} and ϕ→K^{+}K^{-}, using 10.4 fb^{-1} of proton-antiproton collisions collected by the D0 detector during Run II at the Fermilab Tevatron Collider. A fit to the difference between the time-integrated D_{s}^{-} and D_{s}^{+} mass distributions of the B_{s}^{0} and B[over ¯]_{s}^{0} candidates yields the flavor-specific asymmetry a_{sl}^{s}=[-1.12±0.74(stat)±0.17(syst)]%, which is the most precise measurement and in agreement with the standard model prediction.
Physical Review Letters 01/2013; 110(1):011801. · 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,
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
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
A. Askew, [......],
S. W. Youn,
J. M. Yu,
J. Zennamo,
T. Zhao,
T. G. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We present a search for the standard model Higgs boson using events with two oppositely charged leptons and large missing transverse energy as expected in H→WW decays. The events are selected from data corresponding to 8.6 fb-1 of integrated luminosity in pp̅ collisions at √s=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. No significant excess above the standard model background expectation in the Higgs boson mass range this search is sensitive to is observed, and upper limits on the Higgs boson production cross section are derived.
Phys. Rev. D. 08/2012; 86(3).
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
M. Aoki, [......],
H. Yin,
K. Yip,
S. W. Youn,
T. Zhao,
T. G. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: This report describes a search for associated production of W and Higgs bosons based on data corresponding to an integrated luminosity of L≈5.3 fb-1 collected with the D0 detector at the Fermilab Tevatron pp̅ Collider. Events containing a W→ℓν candidate (with ℓ corresponding to e or μ) are selected in association with two or three reconstructed jets. One or two of the jets are required to be consistent with having evolved from a b quark. A multivariate discriminant technique is used to improve the separation of signal and backgrounds. Expected and observed upper limits are obtained for the product of the WH production cross section and branching ratios and reported in terms of ratios relative to the prediction of the standard model as a function of the mass of the Higgs boson (MH). The observed and expected 95% C.L. upper limits obtained for an assumed MH=115 GeV are, respectively, factors of 4.5 and 4.8 larger than the value predicted by the standard model.
Phys. Rev. D. 08/2012; 86(3).
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
G. A. Alves, [......],
K. Yip,
S. W. Youn,
J. Zennamo,
T. Zhao,
T. G. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the elastic differential cross section dσ(pp̅ →pp̅ )/dt as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of ≈31 nb-1 collected with the D0 detector using dedicated Tevatron pp̅ Collider operating conditions at √s=1.96 TeV and covers the range 0.26<|t|<1.2 GeV2. For |t|<0.6 GeV2, dσ/dt is described by an exponential function of the form Ae-b|t| with a slope parameter b=16.86±0.10(stat)±0.20(syst) GeV-2. A change in slope is observed at |t|≈0.6 GeV2, followed by a more gradual |t| dependence with increasing values of |t|.
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 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 CDF,
collaborations,
T. Aaltonen,
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov, [......],
J. Zennamo,
T. Zhao,
T. G. Zhao,
B. Zhou,
C. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic,
S. Zucchelli
[show abstract]
[hide abstract]
ABSTRACT: The top quark is the heaviest known elementary particle, with a mass about 40
times larger than the mass of its isospin partner, the bottom quark. It decays
almost 100% of the time to a $W$ boson and a bottom quark. Using top-antitop
pairs at the Tevatron proton-antiproton collider, the CDF and {\dzero}
collaborations have measured the top quark's mass in different final states for
integrated luminosities of up to 5.8 fb$^{-1}$. This paper reports on a
combination of these measurements that results in a more precise value of the
mass than any individual decay channel can provide. It describes the treatment
of the systematic uncertainties and their correlations. The mass value
determined is $173.18 \pm 0.56 \thinspace ({\rm stat}) \pm 0.75 \thinspace
({\rm syst})$ GeV or $173.18 \pm 0.94$ GeV, which has a precision of $\pm
0.54%$, making this the most precise determination of the top quark mass.
07/2012;
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
M. Aoki, [......],
Z. Ye,
H. Yin,
K. Yip,
S. W. Youn,
T. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We study the processes pp̅ →WZ→ℓ±νℓ+ℓ- and pp̅ →ZZ→ℓ+ℓ-νν̅ , where ℓ=e or μ. Using 8.6 fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider, we measure the WZ production cross section to be 4.50-0.66+0.63 pb which is consistent with, but slightly larger than, the prediction of the standard model. The ZZ cross section is measured to be 1.64±0.46 pb, in agreement with a prediction of the standard model. Combination with an earlier analysis of the ZZ→ℓ+ℓ-ℓ+ℓ- channel yields a ZZ cross section of 1.44-0.34+0.35 pb.
Phys. Rev. D. 06/2012; 85(11).
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
M. Aoki, [......],
K. Yip,
S. W. Youn,
J. Zennamo,
T. Zhao,
T. G. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We measure the Λb0 lifetime in the fully reconstructed decay Λb0→J/ψΛ0 using 10.4 fb-1 of pp̅ collisions collected with the D0 detector at √s=1.96 TeV. The lifetime of the topologically similar decay channel B0→J/ψKS0 is also measured. We obtain τ(Λb0)=1.303±0.075(stat)±0.035(syst) ps and τ(B0)=1.508±0.025(stat)±0.043(syst) ps. Using these measurements, we determine the lifetime ratio of τ(Λb0)/τ(B0)=0.864±0.052(stat)±0.033(syst).
Phys. Rev. D. 06/2012; 85(11).
-
Collaboration,
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson, [......],
K. Yip,
S. W. Youn,
J. Zennamo,
T. Zhao,
T. G. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the elastic differential cross section
$d\sigma(p\bar{p}\rightarrow p\bar{p})/dt$ as a function of the
four-momentum-transfer squared t. The data sample corresponds to an integrated
luminosity of $\approx 31 nb^{-1}$ collected with the D0 detector using
dedicated Tevatron $p\bar{p} $ Collider operating conditions at sqrt(s) = 1.96
TeV and covers the range $0.26 <|t|< 1.2 GeV^2$. For $|t|<0.6 GeV^2$,
d\sigma/dt is described by an exponential function of the form $Ae^{-b|t|}$
with a slope parameter $ b = 16.86 \pm 0.10(stat) \pm 0.20(syst) GeV^{-2}$. A
change in slope is observed at $|t| \approx 0.6 GeV^2$, followed by a more
gradual |t| dependence with increasing values of |t|.
06/2012;
-
V. M. Abazov,
B. Abbott,
B. S. Acharya,
M. Adams,
T. Adams,
G. D. Alexeev,
G. Alkhazov,
A. Alton,
G. Alverson,
G. A. Alves, [......],
K. Yip,
S. W. Youn,
J. Yu,
S. Zelitch,
T. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We describe a model-independent search for physics beyond the standard model in lepton final states. We examine 117 final states using 1.1 fb-1 of pp̅ collisions data at √s=1.96 TeV collected with the D0 detector. We conclude that all observed discrepancies between data and model can be attributed to uncertainties in the standard model background modeling, and hence we do not see any evidence for physics beyond the standard model.
Phys. Rev. D. 05/2012; 85(9).
-
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
-
V M Abazov,
B Abbott,
B S Acharya,
M Adams,
T Adams,
G D Alexeev,
G Alkhazov,
A Alton,
G Alverson,
G A Alves, [......],
H Yin,
K Yip,
S W Youn,
J Yu,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
L Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: We study WW and WZ production with ℓνqq (ℓ=e,μ) final states using data collected by the D0 detector at the Fermilab Tevatron Collider corresponding to 4.3 fb(-1) of integrated luminosity from pp collisions at sqrt[s]=1.96 TeV. Assuming the ratio between the production cross sections σ(WW) and σ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to be σ(WV)=19.6(-3.0)(+3.2) pb and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously fitting WW and WZ contributions, we measure σ(WW)=15.9(-3.2)(+3.7) pb and σ(WZ)=3.3(-3.3)(+4.1) pb, which is consistent with the standard model predictions.
Physical Review Letters 05/2012; 108(18):181803. · 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
