Identification Of B-jets And Observation Of The B(?) Decay Mode Of The Higgs Boson With The ATLAS Experiment

A new particle which is consistent with the Standard Model(SM)Higgs boson has been observed by the ATLAS and CMS experiments in 2012.After that,the property study of the Higgs boson has been extensively performed in bosonic decay channels and entered a new era of precision measurement.However,for the SM Higgs boson with a mass of 125 GeV,the H?b(?) decay mode has not been discovered previously,despite the largest branching ratio of 58%.The search for the inclusive H?b(?) decays is unrealistic due to the large multi-b-jet background at the LHC.The search for the H?b(?) decays has been performed in the VH production mode,with V standing for the W or Z boson.The characteristics of the leptonic decay of the vector boson,Z?vv,W?lv and Z?ll,have been exploited to suppress the background and as the trigger signature during the data-taking.This analysis is based on 79.8 fb-1 of proton-proton collision data collected by the ATLAS detector in the years of 2015 to 2017.In this analysis,an excess of data events over expected Standard Model(SM)background processes is observed,which corresponds to 4.9(4.3)? of observed(expected)significance.The signal strength,which defined as the ratio of the observed cross section of the signal process to the SM predictions,is measured as 1.16±0.26.Further more,with combined to other Higgs boson production modes,the H?b(?) decay has been observed with 5.4(5.5)? of observed(expected)significance.The VH production mode is also observed with 5.3(4.8)? of observed(expected)significance by combining with other Higgs boson decay channels.In the VH,H?b(?) analysis,the Higgs candidate is reconstructed with two hadronic jets which are identified as b-jets.The identification of b-jets,also known as b-tagging,has played an important role in many physics programmes of the ATLAS experiment.The b-tagging efficiency has been measured based on 36.1 fb-1 proton-proton collision data collected by ATLAS detector from 2015 to 2016.In this analysis,the b-tagging efficiency has been measured from a Tag-and-Probe method,and the b-tagging efficiency scale factors are derived as function of jet pT,with total uncertainty ranges from 2%to 12%depending on the jet PT.