Calibration of a soft secondary vertex tagger using proton-proton collisions at $\sqrt{s}=$13 TeV with the ATLAS detector

TL;DR

This paper presents the calibration of a $b$-hadron tagging algorithm using 13 TeV proton-proton collision data from ATLAS, improving $b$-tagging performance estimates for new physics searches.

Contribution

It introduces a calibration method for a soft secondary vertex $b$-tagger using real collision data, with scale factors derived for efficiency and mistag rates across different event conditions.

Findings

Calibration scale factors for $b$-tagging efficiency are obtained.

Mistag rate scale factors are estimated for different interaction levels.

Validated results are applicable to various physics analysis regimes.

Abstract

Several processes studied by the ATLAS experiment at the Large Hadron Collider produce low-momentum $b$-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies $b$-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb$^{-1}$. Scale factors used to correct the algorithm's performance in simulated events are extracted for the $b$-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in $t\bar{t}$ events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a $b$-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average number of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regimes.