Identification of b-quark jets with the CMS experiment

At the Large Hadron Collider, the identification of jets originating from b quarks is important for searches for new physics and for measurements of standard model processes. A vari- ety of algorithms has been developed by CMS to select b-quark jets based on variables such as the impact parameters of charged-particle tracks, the properties of reconstructed decay vertices, and the presence or absence of a lepton, or combinations thereof. The performance of these algorithms has been measured using data from proton-proton collisions at the LHC and compared with expec- tations based on simulation. The data used in this study were recorded in 2011 at p s = 7 TeV for a total integrated luminosity of 5.0 fb 1 . The efficiency for tagging b-quark jets has been measured in events from multijet and t-quark pair production. CMS has achieved a b-jet tagging efficiency of 85% for a light-parton misidentification probability of 10% in multijet events. For analyses requir- ing higher purity, a misidentification probability of only 1.5% has been achieved, for a 70% b-jet tagging efficiency.