May 16 – 20, 2022
Europe/Zurich timezone

Measurement of the b -tagging efficiency using multijet events in ATLAS

May 17, 2022, 7:00 PM
Experimental poster Performance and Tools Poster Session I


Valentina Vecchio (University of Manchester)


The identification of jets containing b-hadrons, b-tagging, plays an important role in many physics analyses in ATLAS. Several different machine learning algorithms have been deployed for the purpose of b-tagging. These tagging algorithms are trained using Monte-Carlo simulation samples, as such their performance in data must be measured. The b-tagging efficiencies (epsilon_b) have been measured in data using $t\bar{t}$ events in the past and this work presents the measurements in multijet events using data collected by the ATLAS detector at $\sqrt{s}=13\rm~ TeV$ for the first time. This offers several key advantages over the ttbar based calibrations, including a higher precision at low jet $p_T$ and an ability to perform measurements of epsilon_b at significantly higher jet $p_T$. Two approaches are applied and for both a profile likelihood fit is performed to extract the number of b-jets in samples passing and failing a given b-tagging requirement. The b-jets yields are then used to determine epsilon_b in data and from that scale factors to the efficiency measured in MC. The two approaches differ primarily in the discriminating variable used in the fit. At low jet $p_T$ the variable ${p_T}_{rel}$ is used, while for high jet $p_T$ the signed impact parameter significance is used. Both calibrations give measurements of the scale factors as a function of the jet $p_T$.

Primary authors

Andreas Korn (University College London (GB)) Valentina Vecchio (University of Manchester)

Presentation materials