https://indico.ihep.ac.cn/event/11467/

This paper describe the latest results of ATLAS b-jet identification performance and efficiency measurement with ttar events.

• The identification of jets containing b-hadrons (b-jets) against the large jet background containing c-hadrons but no b-hadron (c-jets) or containing neither b- or c-hadrons (light-flavour jets) is of major importance in many areas of the physics programme of the ATLAS experiment, plays a crucial role in a large number of Standard Model (SM) precision measurements, studies of the Higgs boson properties, and searches for new phenomena.

• The most impoartant feature of b-jet is that it contains a b hadron which has a long life time, with the help of inner detector of ATLAS, we can reconstruct the secondary vertex of the b-badron.

• Several algorithms have been developed to identify the b-jet: – Low-level identifications: IP2D, IP3D, SV1, JetFitter – High-level identification: MV2 and DL1

• Events are classifies into one signal region(rich in ttbar events) and 3 control regions(rich in background events)

• Mimimum likelihood methos is employed to extract the b-tag efficiency in each pT region of the signal region,

• The derived efficiencies from data and MC agree well, the scale factors are close to one.