Jeff Tseng

Abstract:

An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6fb-1 of integrated luminosity collected in 2011 at √s=7TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with p T>20GeV and |η|<2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(μμ) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(μμ) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e.g. doubly charged Higgs bosons (H ±). Assuming pair production of H± bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244)GeV and 251 (209)GeV for H± bosons coupling to left-handed and right-handed fermions, respectively. © 2012 CERN. Published by the American Physical Society under the terms of the uri xlink:href=http://creativecommons.org/licenses/by/3.0/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 DOI. © 2012 American Physical Society.

Abstract:

A measurement is presented of the cross section for the production of a W boson with one or two jets, of which at least one must be a b-jet, in pp collisions at s=7TeV. Production via top decay is not included in the signal definition. The measurement is based on 35pb -1 of data collected with the ATLAS detector at the LHC. The W+b-jet cross section is defined for jets reconstructed with the anti-k t clustering algorithm with transverse momentum above 25 GeV and rapidity within ±2.1. The b-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay channel of the W boson and is found to be 10.2±1.9(stat)±2.6(syst)pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent with, the measured value. © 2011 CERN.

Abstract:

A measurement of the production cross section of top quark pairs (tt̄) 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 35pb-1, a tt̄ production cross section σtt̄=177±20(stat.)±14(syst.)±7(lum.)pb is measured for an assumed top quark mass of mt=172.5GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions. © 2011 CERN.

Abstract:

This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of s=7TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4

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