Calibration of the $b$-tagging efficiency on charm jets using a sample of $W$+$c$ events with $\sqrt{s}$ = 13 TeV ATLAS data

The identification of jets containing $b$-hadrons ($b$-jets) is of fundamental importance for many physics analyses performed by the ATLAS experiment. The measurement of the probability to mistakenly identify a jet containing $c$-hadrons ($c$-jet) as a $b$-jet, referred to as the $c$-jet tagging efficiency, is presented. The analysis is performed using a sample of $c$-jets produced in association with a $W$ boson, extracted from $pp$ collisions recorded at $\sqrt{s}$ = 13 TeV during 2015 and 2016, corresponding to an integrated luminosity of approximately 36 $fb^{-1}$. The $W$ boson is identified by an isolated electron and missing transverse energy from the neutrino, and the $c$-jet is identified by a muon stemming from a semileptonic $c$-hadron decay. Data-to-simulation scale factors for the $c$-jet tagging efficiency are computed for calorimeter jets reconstructed using the anti-$k_t$ algorithm with a radius parameter of 0.4. Results are presented for the 60\%, 70\%, 77\% and 85\% efficiency working points of the MV2c10 $b$-jet identification algorithm, integrated and as a function of jet transverse momentum. The results of the measurement performed on $W$+$c$ events are combined with the results of a measurement performed on $t\bar{t}$ events in order to reduce the total uncertainty.