708 research outputs found
Response of Single Isolated Hadrons in the ATLAS Calorimeter
No full textTalk at PLHC about E/p measurement using the 900 GeV dat
Top-quark production at ATLAS
No full textStudies of the top-quark are an important part of the ATLAS physics program. Such studies offer a precision test of the Standard Model, but could also reveal hints of new phenomena. A short summary of the most recent ATLAS results on the study of top-quark production are presented here
Dijet Angular Distributions at the ATLAS Experiment
No full textDijet angular distributions from the first proton-proton collisions at 7 TeV have been measured with the ATLAS detector at the LHC. The dataset used corresponds to a total integrated luminosity of 61 +/- 7 nb-1. Comparing the distributions with Monte Carlo based QCD predictions shows good agreement between data and QCD. The distributions are used to set limits on the existence of quark compositeness
Top Production at ATLAS
No full textTop production with ATLAS (including single top and Afb). A summary of various public top production results produced by ATLAS until now, with a focus on more recent results, and with an outlook on the future
Response of Single Isolated Hadrons in the First ATLAS Data at = 900 GeV
No full textThe response of single isolated hadrons in the ATLAS calorimeters has been studied in 360 thousand collision events at 900 GeV collected during the December 2009 LHC commissioning run. Good agreement is found between the data collected and the Monte Carlo predictions. The results will be used as an input to the estimation of the Jet Energy Scale at ATLAS
Search for a fermiophobic Higgs boson in the diphoton decay channel with the ATLAS detector
No full textA search for a fermiophobic Higgs boson using diphoton events produced in proton-proton collisions at a centre-of-mass energy of s=7 TeV is performed using data corresponding to an integrated luminosity of 4.9 fb−1 collected by the ATLAS experiment at the Large Hadron Collider. A specific benchmark model is considered where all the fermion couplings to the Higgs boson are set to zero and the bosonic couplings are kept at the Standard Model values (fermiophobic Higgs model). The largest excess with respect to the background-only hypothesis is found at 125.5 GeV, with a local significance of 2.9 standard deviations, which reduces to 1.6 standard deviations when taking into account the look-elsewhere effect. The data exclude the fermiophobic Higgs model in the ranges 110.0–118.0 GeV and 119.5–121.0 GeV at 95 % confidence level
Strong constraints on jet quenching in centrality-dependent +Pb collisions at 5.02 TeV from ATLAS
No full textJet quenching is the process of color-charged partons losing energy via interactions with quark-gluon plasma droplets created in heavy-ion collisions. The collective expansion of such droplets is well described by viscous hydrodynamics. Similar evidence of collectivity is consistently observed in smaller collision systems, including and +Pb collisions. In contrast, while jet quenching is observed in Pb+Pb collisions, no evidence has been found in these small systems to date, raising fundamental questions about the nature of the system created in these collisions. The ATLAS experiment at the Large Hadron Collider has measured the yield of charged hadrons correlated with reconstructed jets in 0.36 nb of +Pb and 3.6 pb of collisions at 5.02 TeV. The yields of charged hadrons with GeV near and opposite in azimuth to jets with or 60 GeV, and the ratios of these yields between +Pb and collisions, , are reported. The collision centrality of +Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The values are consistent with unity within a few percent for hadrons with GeV at all centralities. These data provide new, strong constraints which preclude almost any parton energy loss in central +Pb collisions
Search for pair production of massive particles decaying into three quarks with the ATLAS detector in root s=7 TeV pp collisions at the LHC
No full textATLAS Collaboration Contributor: P. JacksonA search is conducted for hadronic three-body decays of a new massive coloured particle in √s=7 TeV pp collisions at the LHC using an integrated luminosity of 4.6 fb−1 collected by the ATLAS detector. Supersymmetric gluino pair production in the context of a model with R-parity violation is used as a benchmark scenario. The analysis is divided into two search channels, each optimised separately for their sensitivity to high-mass and low-mass gluino production. The first search channel uses a stringent selection on the transverse momentum of the six leading jets and is performed as a counting experiment. The second search channel focuses on low-mass gluinos produced with a large boost. Large-radius jets are selected and the invariant mass of each of the two leading jets is used as a discriminant between the signal and the background. The results are found to be consistent with Standard Model expectations and limits are set on the allowed gluino mass.The ATLAS collaboratio
Transverse momentum, rapidity, and centrality dependence of inclusive charged-particle production in TeV p+Pb collisions measured by the ATLAS experiment
No full text22 pages plus author list + cover page (41 pages total), 9 figures, 4 tables, submitted to Phys. Lett. B, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2012-14/ - See paper for full list of authorsInternational audienceMeasurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of TeV. Charged particles are reconstructed over pseudorapidity and transverse momentum between GeV and GeV in a dataset corresponding to an integrated luminosity of . The results are presented in the form of charged-particle nuclear modification factors, where the Pb charged-particle multiplicities are compared between central and peripheral Pb collisions as well as to charged-particle cross sections measured in pp collisions. The Pb collision centrality is characterized by the total transverse energy measured in , which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the Pb collision are carried out using the Glauber model and two Glauber-Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus
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