Measurement of the top-quark mass using a leptonic invariant mass in $pp$ collisions at $\sqrt{s}=13\text{ TeV}$ with the ATLAS detector

A measurement of the top-quark mass ($m_t$) in the $t\bar{t}\to \text{ lepton}+\text{jets}$ channel is presented, with an experimental technique which exploits semileptonic decays of $b$-hadrons produced in the top-quark decay chain. The distribution of the invariant mass $m_{\mathrm{\ell }\mu }$ of the lepton, $\mathrm{\ell }$ (with $\mathrm{\ell }=e,\mu$), from the $W$-boson decay and the muon, $\mu$, originating from the $b$-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract $m_t$. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb${}^{-1}$ of $\sqrt{s}=13\text{ TeV}$ $pp$ collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is $m_t=174.41\pm 0.39(\text{stat.})\pm 0.66(\text{syst.})\pm 0.25(\text{recoil})\text{ GeV}$, where the third uncertainty arises from changing the PYTHIA8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.