0000000000318030
AUTHOR
H Przysiezniak
Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in $pp$ collisions at $\sqrt{s}=7$ TeV
In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at s√=7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb[superscript −1] collected with the ATLAS detector in 2011. The pT spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production…
Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data
Acknowledgements We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; ARTEMIS, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo…
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at √s = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton–proton collisions at a centre-of-mass energy of √s =7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb[superscript −1]. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the ra…
Search for supersymmetry in events with large missing transverse momentum, jets, and at least one tau lepton in 7 TeV proton-proton collision data with the ATLAS detector
A search for supersymmetry (SUSY) in events with large missing transverse momentum, jets, and at least one hadronically decaying τ lepton, with zero or one additional light lepton (e/μ), has been performed using 4.7 fb[superscript −1] of proton-proton collision data at √s = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95 % confidence level visible cross-sectionupper limit for new phenomena is set. In the framework of gauge-mediated SUSY-breaking models, lower limits on the mass scale Λ are set at 54 TeV in the regions where the [bar over τ]1 is the next-to-lightest SUSY particle (tanβ > 20). …
Search for scalar leptons in e+e- collisions at centre-of-mass energies up to 209 GeV
A search for selectron, smuon and stau pair production is performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. The numbers of candidate events are consistent with the background predicted by the Standard Model. Final mass limits from ALEPH are reported.
Improved luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC
The luminosity calibration for the ATLAS detector at the LHC during pp collisions at sqrt(s) = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at sqrt(s) = 7 TeV. A luminosity uncertainty of Delta L/L = +/- 3.5% is obtained for the 47 pb-1 of data delivered to ATLAS in 2010, and an uncertainty of Delta L/L = +/- 1.8% is obtained for the 5.5 fb-1 delivered in 2011.
Studies of the performance of the ATLAS detector using cosmic-ray muons
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 calibrat…
Search for an invisibly decaying Higgs boson in e+e-collisions at 189 GeV
The data collected in 1998 by ALEPH at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.2 pb(-1), are analysed to search for invisible decays of a Higgs boson produced in the reaction e(+) e(-) --> hZ. The number of events found in the data and their properties art: in agreement with the Standard Model expectation. This search results in an improved 95% C.L. lower limit on the Higgs boson mass of 95.4 GeV/c(2), assuming it decays totally invisibly and for a production cross section equal to that of the Standard Model. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Measurement of the W mass in e+e− collisions at 183 GeV
Abstract The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 57 pb−1 collected with the ALEPH detector in 1997 at a centre-of-mass energy of 183 GeV. The invariant mass distributions of reweighted Monte Carlo events are fitted separately to the experimental distributions in the q q q q and all lν q q channels to give the following W masses: m W hadronic =80.461±0.177 (stat.) ±0.045 (syst.) ±0.056 (theory) GeV /c 2 , m W semileptonic =80.326±0.184 (stat.) ±0.040 (syst.) GeV /c 2 , where the theory error represents the possible effects of final state interactions. The combination of these two measurements…
Search for massive colored scalars in four-jet final states in √s = 7 TeV proton–proton collisions with the ATLAS detector
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 34 pb[superscript −1] recorded by the ATLAS detector in 2010. No deviation from the Standard Model is observed. For a scalar mass of 100 GeV (190 GeV) the limit on the scalar gluon pair production cross section at 95% confidence level is 1 nb (0.28 nb). When these results are interpreted as mass limits, scalar-gluons (hyperpions) with masses of 100 to 185 GeV (100 to 155 GeV) are excluded at 95% confidence level with the exception of a mass window of width about 5 GeV (15 GeV) around 140 GeV.
Single- and multi-photon production in e+e− collisions at a centre-of-mass energy of 183 GeV
The production of final states involving one or more energetic photons from e(+)e(-) collisions is studied in a sample of 58.5 pb(-1) of data recorded at a centre-of-mass energy of 183 GeV by the ALEPH detector at LEP. The e(+)e(-) --> v (v) over bar gamma(gamma) and e(+)e(-) --> gamma gamma(gamma) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e…
Search for light scalar top quark pair production in final states with two leptons with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions
A search is presented for the pair production of light scalar top quarks in s√=7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 running that corresponds to a total integrated luminosity of 4.7 fb[superscript −1]. Light scalar top quarks are searched for in events with two opposite-sign leptons (e, μ), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through…
Search for invisible Higgs boson decays in e+e- collisions at centre-of-mass energies up to 184 GeV
In a data sample of 78.3 pb(-1) collected in 1996 and 1997 by the ALEPH detector at centre-of-mass energies from 161 to 184 GeV, invisible decays of a Higgs boson have been searched for in the reaction e(+)e(-) --> hZ, where the Z can decay into e(+)e(-), mu(+) mu(-) or . No evidence for a signal is found and limits on the production cross section are derived as a function of the Higgs boson mass. These results are combined with those obtained in an update of the analyses of the ALEPH data taken at LEP 1. For a production cross section equal to that of the minimal standard model Higgs boson, masses below 80 GeV/c(2) are excluded at 95% C.L. (C) 1999 Elsevier Science B.V. All rights reserved.
Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS detector
A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton–proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb−1. A total of 7 candidate events are o…
Search for supersymmetric particles in events with lepton pairs and large missing transverse momentum in sqrt{s} = 7 TeV proton-proton collisions with the ATLAS experiment
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 √ s = 7 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 35 pb−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 690 GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy…
Search for pair-produced massive coloured scalars in four-jet final states with the ATLAS detector in proton–proton collisions at √s =7 TeV
A search for pair-produced massive coloured scalar particles decaying to a four-jet final state is performed by the ATLAS experiment at the LHC in proton–proton collisions at √s = 7 TeV. The analysed data sample corresponds to an integrated luminosity of 4.6 fb[superscript −1]. No deviation from the Standard Model is observed in the invariant mass spectrum of the two-jet pairs. A limit on the scalar gluon pair production cross section of 70 pb (10 pb) is obtained at the 95 % confidence level for a scalar gluon mass of 150 GeV (350 GeV). Interpreting these results as mass limits on scalar gluons, masses ranging from 150 GeV to 287 GeV are excluded at the 95 % confidence level.
Four-jet final state production in $e^+ e^-$ collisions at centre-of-mass energies ranging from 130 to 184 GeV
The four jet topology is analysed in the ALEPH data taken between November 1995 and November 1997, at centre-of-mass energies ranging from 130 to 184 GeV. While an unexpected accumulation of events with a dijet mas sum around 105 GeV/c**2 had been observed during the first run in 1995 at 130/136 GeV, corresponding to an integrated luminosity of 5.7 pb-1, no significant differences between data and standard model prediction is noticed, either in the high energy runs (81.1 pb-1 taken at centre-of-mass energies from 161 to 184 GeV) or in the 7.1 pb-1 recorded during a new short run at 130/136 GeV in 1997. We have found no other explanation for the earlier reported ``four jet anomaly'' than a s…
Search for a heavy top-quark partner in final states with two leptons with the ATLAS detector at the LHC
The results of a search for direct pair production of heavy top-quark partners in 4.7 fb[superscript −1] of integrated luminosity from pp collisions at s√ = 7 TeV collected by the ATLAS detector at the LHC are reported. Heavy top-quark partners decaying into a top quark and a neutral non-interacting particle are searched for in events with two leptons in the final state. No excess above the Standard Model expectation is observed. Limits are placed on the mass of a supersymmetric scalar top and of a spin-1/2 top-quark partner. A spin-1/2 top-quark partner with a mass between 300 GeV and 480 GeV, decaying to a top quark and a neutral non-interacting particle lighter than 100 GeV, is excluded …
Performance of the ATLAS detector using first collision data
More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track- and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies.