11 research outputs found
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
No full textThe jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy ofs√=7 TeV corresponding to an integrated luminosity of 38 pb−1. Jets are reconstructed with the anti-k t algorithm with distance parameters R=0.4 or R=0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta p T≥20 GeV and pseudorapidities |η|<4.5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2.5 % in the central calorimeter region (|η|<0.8) for jets with 60≤p T<800 GeV, and is maximally 14 % for p T<30 GeV in the most forward region 3.2≤|η|<4.5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon p T, the sum of the transverse momenta of tracks associated to the jet, or a system of low-p T jets recoiling against a high-p T jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-p T jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined
Measurement of the top quark charge in pp collisions at s√=7 TeV with the ATLAS detector
No full textA measurement of the top quark electric charge is carried out in the ATLAS experiment at the Large Hadron Collider using 2.05 fb−1 of data at a centre-of-mass energy of 7 TeV. In units of the elementary electric charge, the top quark charge is determined to be 0.64 ± 0.02 (stat.) ± 0.08 (syst.) from the charges of the top quark decay products in single lepton tt¯ candidate events. This excludes models that propose a heavy quark of electric charge −4/3, instead of the Standard Model top quark, with a significance of more than 8σ
Jet energy resolution in proton-proton collisions at root s=7 TeV recorded in 2010 with the ATLAS detector
No full textAtlas Collaboration contributor: Paul Douglas Jackson of SLAC National Accelerator Laboratory, Stanford CA, United States of America. Extent: 27p.The measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton collisions at √s=7 TeV . The sample corresponds to an integrated luminosity of 35 pb⁻¹. Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within |y|<2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.The ATLAS Collaboratio
Search for heavy stable and longlived particles in e+ e- collisions at s**(1/2) = 189-GeV
No full textA search for stable and long-lived heavy charged particles was performed using the data taken by the DELPHI experiment at an energy of 189 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionisation loss measured in the Time Projection Chamber were used to identify heavy particles passing through the detector. No evidence for the production of such particles has been found, therefore exclusion limits at 95% confidence level were derived on the masses of left and right handed smuons and staus. The results were combined with previous DELPHI searches in this channel. Including previous DELPHI results, masses of left (right) handed stable smuons and staus can be excluded between 2 GeV/c2 and 88 (87.5) GeV/c2 at 95% CL.0info:eu-repo/semantics/publishe
Measurement of the electron structure function F-2(e) at LEP energies
No full textThe hadronic part of the electron structure function F2e has been measured for the first time, using e +e - data collected by the DELPHI experiment at LEP, at centre-of-mass energies of s=91.2-209.5GeV. The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function F2e data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function F2γ analyses and help in refining existing parameterisations. © 2014 The Authors. Elsevier B.V
Inclusive single-particle production in two-photon collisions at LEP II with the DELPHI detector
No full textA study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle pT distribution and the differential charged hadrons dσ/dpT cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results
The ATLAS inner detector commissioning and calibration
No full textThe ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1±0.9 μm and a relative momentum resolution σ p /p=(4.83±0.16)×10<sup>−4</sup> GeV<sup>−1</sup>×p T have been measured for high momentum tracks
Search for heavy particles decaying into top-quark pairs using lepton-plus-jets events in proton--proton collisions at TeV with the ATLAS detector
No full textA search for new heavy particles that decay into top-quark pairs is performed using data collected from proton--proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain -hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical bosons, Kaluza--Kein gluons and Kaluza--Klein gravitons that decay into top-quark pairs.A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13 by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb . Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain b-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs.A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton-proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain -hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical bosons, Kaluza-Kein gluons and Kaluza-Klein gravitons that decay into top-quark pairs
Search for exclusive Higgs and boson decays to and with the ATLAS Detector
No full textA search for the exclusive decays of the Higgs and bosons to a or meson and a photon is performed with a collision data sample corresponding to an integrated luminosity of up to collected at with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson coupling to light quarks. No significant excess of events is observed above the background, in agreement with the Standard Model expectations. Upper limits at 95\% confidence level on the branching fractions of the Higgs boson decays to and of and , respectively, are obtained. The corresponding 95\% confidence level upper limits for the boson decays are and for and , respectively
Measurement of the electron structure function F e 2 at LEP energies DELPHI Collaboration
No full textThe hadronic part of the electron structure function F e 2 has been measured for the first time, using e + e − data collected by the DELPHI experiment at LEP, at centre-of-mass energies of The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function F e 2 data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function F γ 2 analyses and help in refining existing parameterisations
