Measuring the b-tagging Performance with ATLAS Data

The identification of jets originating from b-quarks, referred to as b-tagging, is an important part of the LHC physics program. Most b-tagging algorithms exploit the relatively long lifetime of the b-hadron, resulting in a second decay vertex which is significantly displaced from the primary interaction point. In precision measurements in the top quark sector as well as in the search for the Higgs boson and new phenomena, the suppression of background processes containing predominantly light-flavour jets using b-tagging is of great use. It is also critical to eventually understand the flavour structure of any new physics (e.g. supersymmetry) that may be revealed at the LHC. In order for b-tagging to be used in physics analyses the efficiency with which a jet originating from a b-quark is tagged by a b-tagging algorithm needs to be measured. A second important piece of information is the probability to tag a jet originating from a light-flavour (u-, d-, s-quark or gluon) jet, referred to as the mistag rate. Both the b-tag efficiency and the mistag rate have been measured with data from the ATLAS detector using a range of methods. The b-tag efficiency measurements either make use of samples of jets containing muons or a ample of top quark events which inherently contains a large fraction of b-jets, while the mistag rate is measured in a QCD jet sample.