Measurements of <i>b</i>-jet tagging efficiency with the ATLAS detector using <i>t¯t</i> events at √s = 13 TeV

Abstract

The efficiency to identify jets containing <i>b</i>-hadrons (<i>b</i>-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs (<i>t¯t</i>) selected from the 36.1 fb^-1 of data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy √s = 13TeV. Two methods are used to extract the efficiency from <i>t¯t</i> events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using <i>b</i>-tagging information, is used to select events in which two <i>b</i>-jets are present, which reduces the dominant uncertainty in the modelling of the avour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.