# ATLAS $b$-jet identification performance and efficiency measurement with $t\bar{t}$ events in $pp$ collisions at $\sqrt{s}=13$ TeV

## TL;DR

This paper evaluates the performance and efficiency of $b$-jet identification algorithms used by ATLAS during Run 2, using $tar{t}$ events at 13 TeV, and compares measurements with simulation predictions.

## Contribution

It introduces a likelihood-based method to measure $b$-jet tagging efficiency in $tar{t}$ events, improving precision over previous measurements.

## Key findings

- Efficiency uncertainties range from 1% to 8%.
- Measurement agrees well with simulation predictions.
- Enhanced precision in $b$-jet identification performance.

## Abstract

The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing $b$-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing $b$-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample of highly enriched in $t\bar{t}$ events. The topology of the $t \to W b$ decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 GeV to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb$^{-1}$, were collected in proton-proton collisions during the years 2015 to 2017 at a centre-of-mass energy $\sqrt{s}=$ 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1% to 8% depending on the jet transverse momentum.