[Show abstract][Hide abstract] ABSTRACT: A search is made for massive long-lived highly ionising particles with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb-1 of pp collision data taken at sqrt(s)=7 TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e <= |q| <= 17e and masses 200 GeV <= m <= 1000 GeV are set in the range 1-12 pb for different hypotheses on the production mechanism.
[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. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement of the cross-section for
ϒ(1S)→μμ production in
proton-proton collisions at centre of mass energy of 7 TeV is presented.
The cross-section is measured as a function of the ϒ(1S)
transverse momentum in two bins of rapidity, |y|<1.2 and
1.2<|y|<2.4. The measurement requires that both muons
have transverse momentum pTμ>4 GeV and pseudorapidity
|η|<2.5 in order to reduce theoretical uncertainties
on the acceptance, which depend on the poorly known polarisation. The
results are based on an integrated luminosity of 1.13 pb-1,
collected with the ATLAS detector at the Large Hadron Collider. The
cross-section measurement is compared to theoretical predictions: it
agrees to within a factor of two with a prediction based on the NRQCD
model including colour-singlet and colour-octet matrix elements as
implemented in PYTHIA while it disagrees by up to a factor of ten with
the next-to-leading order prediction based on the colour-singlet model.
Physics Letters B 10/2011; 705:9-27. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for new phenomena in events featuring a high energy jet and
large missing transverse momentum in proton-proton collisions at s = 7
TeV is presented using a dataset corresponding to an integrated
luminosity of 33 pb -1 recorded with the ATLAS detector at
the Large Hadron Collider. The number of observed events is consistent
with the Standard Model prediction. This result is interpreted in terms
of limits on a model of Large Extra Dimensions.
Physics Letters B 10/2011; 705:294-312. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for long-lived charged particles reaching the muon spectrometer
is performed using a data sample of 37 pb - 1 from pp
collisions at s = 7 TeV collected by the ATLAS detector at the LHC in
2010. No excess is observed above the estimated background. Stable τ
˜ sleptons are excluded at 95% CL up to a mass of 136 GeV , in
GMSB models with N = 3 , m = 250 TeV , sign (
μ ) = 1 and tan β = 5 . Electroweak production of sleptons is
excluded up to a mass of 110 GeV . Gluino R -hadrons in a generic
interaction model are excluded up to masses of 530 GeV to 544 GeV
depending on the fraction of R -hadrons produced as g ˜ -balls.
Physics Letters B 08/2011; 703:428-446. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The inclusive J/ψ production cross-section and fraction of J/ψ
mesons produced in B-hadron decays are measured in proton-proton
collisions at s=7 TeV with the ATLAS detector at the LHC, as a function
of the transverse momentum and rapidity of the J/ψ, using 2.3
pb-1 of integrated luminosity. The cross-section is measured
from a minimum p of 1 GeV to a maximum of 70 GeV and for
rapidities within |y|<2.4 giving the widest reach of any measurement
of J/ψ production to date. The differential production
cross-sections of prompt and non-prompt J/ψ are separately
determined and are compared to Colour Singlet NNLO⋆,
Colour Evaporation Model, and FONLL predictions.
Nuclear Physics B 08/2011; 850:387-444. · 4.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This Letter presents a measurement of the W+ W- production cross section in sqrt(s) = 7 TeV pp collisions by the ATLAS experiment, using 34 pb(-1) of integrated luminosity produced by the Large Hadron Collider at CERN. Selecting events with two isolated leptons, each either an electron or a muon, 8 candidate events are observed with an expected background of 1.7 ± 0.6 events. The measured cross section is 41(-16)(+20)(stat) ± 5(syst)±1(lumi) pb, which is consistent with the standard model prediction of 44 ± 3 pb calculated at next-to-leading order in QCD.
[Show abstract][Hide abstract] ABSTRACT: This Letter presents the first search for a heavy particle decaying into an e ± μ(-/+) final state in sqrt[s] = 7 TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except λ(311)' = 0.11 and λ312 = 0.07. In a lepton flavor violating model, a Z'-like vector boson with masses of 0.70-1.00 TeV and corresponding cross sections times branching ratios of 0.175-0.183 pb is excluded. These results extend to higher mass R-parity violating sneutrinos and lepton flavor violating Z's than previous constraints from the Tevatron.
[Show abstract][Hide abstract] ABSTRACT: This Letter presents a search for high mass e+e-
or μ+μ- resonances in pp collisions at s=7
TeV at the LHC. The data were recorded by the ATLAS experiment during
2010 and correspond to a total integrated luminosity of ˜40
pb-1. No statistically significant excess above the Standard
Model expectation is observed in the search region of dilepton invariant
mass above 110 GeV. Upper limits at the 95% confidence level are set on
the cross section times branching ratio of Z′
resonances decaying to dielectrons and dimuons as a function of the
resonance mass. A lower mass limit of 1.048 TeV on the Sequential
Standard Model Z′ boson is derived, as well as mass
limits on Z* and E-motivated Z′
Physics Letters B 05/2011; 700:163-180. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb− 1, dijet mass and angular distributions were measured up to dijet masses of ~3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale Λ below 9.5 TeV.
New Journal of Physics 05/2011; 13(5):053044. · 4.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurements are presented from proton–proton collisions at centre-of-mass energies of , 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT>100 MeV, is measured to be 3.483±0.009 (stat)±0.106 (syst) at and 5.630±0.003 (stat)±0.169 (syst) at .
New Journal of Physics 05/2011; 13(5):053033. · 4.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consist of three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by a differential Fabry-Perot interferometer. We plan to launch DECIGO in middle of 2020s, after sequence of two precursor satellite missions, DECIGO pathfinder and Pre-DECIGO, for technology demonstration required to realize DECIGO and hopefully for detection of gravitational waves from our galaxy or nearby galaxies.
Classical and Quantum Gravity 05/2011; · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full data set (∫Ldt=36 pb(-1)) acquired by the ATLAS detector during the 2010 sqrt(s)=7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high-energy regime.
[Show abstract][Hide abstract] ABSTRACT: This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from √s=7 TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A(0)=0 GeV, tanβ=3, and μ>0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.
[Show abstract][Hide abstract] ABSTRACT: Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.
European Physical Journal C 03/2011; 71:1593. · 5.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s=7 TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1 pb⁻¹. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R<729 GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the ATLAS collaboration’s ﬁrst search for supersymmetry in ﬁnal states containing jets, missing transverse momentum and one isolated electron or muon from √s = 7 TeV proton-proton collisions at the LHC. The data have been collected during 2010 and correspond to a total integrated luminosity of 35 pb −1 . No excess above the Standard Model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending earlier limits. For A0 = 0 GeV, tan β = 3, µ > 0 and assuming equal squark and gluino masses, gluino masses below 700 GeV are excluded with 95% conﬁdence level.