2,175 research outputs found
Measurements of top quark pair relative differential cross-sections with ATLAS in pp collisions at root s=7 TeV
No full textATLAS Collaboration Contributor: Paul Douglas Jackson of SLAC National Accelerator Laboratory, Stanford CA, United States of AmericaMeasurements are presented of differential cross-sections for top quark pair production in pp collisions at √s = 7 TeV relative to the total inclusive top quark pair production cross-section. A data sample of 2.05 fb⁻¹ recorded by the ATLAS detector at the Large Hadron Collider is used. Relative differential cross-sections are derived as a function of the invariant mass, the transverse momentum and the rapidity of the top quark pair system. Events are selected in the lepton (electron or muon) + jets channel. The background-subtracted differential distributions are corrected for detector effects, normalized to the total inclusive top quark pair production cross-section and compared to theoretical predictions. The measurement uncertainties range typically between 10 % and 20 % and are generally dominated by systematic effects. No significant deviations from the Standard Model expectations are observed.The ATLAS Collaboratio
Measurement of the b-hadron production cross section using decays to D∗ +μ −X final states in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV with the ATLAS detector
No full textThe b-hadron production cross section is measured with the ATLAS detector in pp collisions at
√<span style="text-decoration:overline">s</span>=7 TeV, using 3.3 pb−1
of integrated luminosity, collected during the 2010 LHC run. The b-hadrons
are selected by partially reconstructing D∗+μ
−X final states. Differential cross sections are measured as
functions of the transverse momentum and pseudorapidity. The measured production cross section for a
b-hadron withpT
>9 GeV and |η|<2.5 is 32.7±0.8(stat.)+4.5
−6.8
(syst.) µb, higher than the next-to-leadingorder QCD predictions but consistent within the experimental and theoretical uncertainties
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV with the ATLAS detector
No full textThe 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−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 range 20<p T<400 GeV and rapidity in the range |y|<2.1. The bb− -dijet cross-section is measured as a function of the dijet invariant mass in the range 110<m jj<760 GeV, the azimuthal angle difference between the two jets and the angular variable χ in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bb− -dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta
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 dilepton resonances in pp collisions at √s=7 TeV with the ATLAS detector
No full textThis Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at √s=7 TeV at the Large Hadron Collider and correspond to a total integrated luminosity of 1.08 (1.21) fb-1 in the e+e- (μ+μ-) channel. No statistically significant excess above the standard model expectation is observed and upper limits are set at the 95% C.L. on the cross section times branching fraction of Z′ resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the sequential standard model Z′ boson is set. A Randall-Sundrum graviton with coupling k/M̅ Pl=0.1 is excluded at 95% C.L. for masses below 1.63 TeV
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
Measurement of the top quark pair production cross section in <i>pp</i> collisions at √s=7 TeV in dilepton final states with ATLAS
No full textA measurement of the production cross section of top quark pairs (t<span style="text-decoration: overline">t</span>) in proton–proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb<sup>−1</sup>, a t<span style="text-decoration: overline">t</span> production cross section σ t<span style="text-decoration: overline">t</span> = 177 ± 20(stat.) ± 14 (syst.) ± 7(lum.) pb is measured for an assumed top quark mass of <i>mt</i>=172.5 GeV. A second measurement requiring at least one jet identified as coming from a <i>b</i> quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by <i>b</i>-quark jets. These measurements are in good agreement with Standard Model predictions
Evidence of W gamma gamma Production in pp Collisions at root s=8 TeV and Limits on Anomalous Quartic Gauge Couplings with the ATLAS Detector
No full textPublished by the American Physical Society under the terms of
the Creative Commons Attribution 3.0 License. Further distribution
of this work must maintain attribution to the author(s) and
the published article’s title, journal citation, and DOISCOAP
Measurement of the inelastic proton–proton cross-section at √s=7 TeV with the ATLAS Detector
No full textA first measurement of the inelastic cross-section is presented for proton-proton collisions at a center of mass energy √ =7 TeV using the ATLAS detector at the Large Hadron Collider. In a dataset corresponding to an integrated luminosity of 20 µb<sup>-1</sup>, events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3 ± 2.1 mb is measured for ξ>5x10<sup>-6</sup>, where ξ=M<sup>2</sup><sub>X</sub>/s is calculated from the invariant mass, M<sub>X</sub>, of hadrons selected using the largest rapidity gap in the event. For diffractive events this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV
Search for type-III seesaw heavy leptons in pp collisions at root s=8 TeV with the ATLAS detector
No full textA search for the pair production of heavy leptons (N-0, L-+/-) predicted by the type-III seesaw theory formulated to explain the origin of small neutrino masses is presented. The decay channels N-0 -> W(+/-)l(+/-) (l = e, mu, tau) and L-+/- -> W(+/-)v (v = v(e), v(mu), v(tau)) are considered. The analysis is performed using the final state that contains two leptons (electrons or muons), two jets from a hadronically decaying W boson and large missing transverse momentum. The data used in the measurement correspond to an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV collected by the ATLAS detector at the LHC. No evidence of heavy lepton pair production is observed. Heavy leptons with masses below 325-540 GeV are excluded at the 95% confidence level, depending on the theoretical scenario considered.ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1103/PhysRevD.92.032001</p
- …
