Göttingen 2012 – scientific programme

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T: Fachverband Teilchenphysik

T 36: Top-Quark: Zerfälle

T 36.3: Talk

Friday, March 2, 2012, 09:15–09:30, ZHG 104

Calibration of b-tagging algorithms using kinematic selections in the single lepton channel tt decays in pp collisions at √s=7 TeV with the ATLAS experiment — Tatevik Abajyan, Markus Cristinziani, Sara Ghasemi, Gia Khoriauli, •Agnieszka Leyko, Ralph Schaefer, Kirika Uchida, and Kaven Yau — Physikalisches Institut Universität Bonn

In the signature of the top pair decays with single lepton in final state there are at least four jets present among which at least two are b-jets. This b-enriched sample provides a perfect environment for the calibration of b-tagging algorithms. Calibration with tt processes takes advantage of the large cross-section of the top quark pair production at the LHC and a good understanding of this process after the initial phase of data taking with the ATLAS detector. Results of such performance studies can be applied to analyses with large multiplicity of high p_T jets, for example Higgs and SUSY searches.

To measure the b-tagging efficiency in the single lepton channel a slightly modified tag and probe method is applied to four jets with the highest p_T in tt events selected from the data recorded by the ATLAS detector. The method accounts also for presence of misidentified c− and light jets, which are coming mostly from the background processes such as W boson production with associated jets or QCD. Thanks to the large amount of data collected in 2011 those studies are not much affected by statistical uncertainty and an accurate measurement of the efficiencies in many jet p_T bins for jets with p_T up to 300 GeV is possible.