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

A measurement for the top-quark mass $m_t$ in the $\ell$+jets channel for $t\bar{t}$ events is presented, with an experimental technique used for the first time in ATLAS. Semi-leptonic decays of $b$-hadrons produced by the same top which produced the leptonically decaying $W$-boson are exploited. The distribution of the invariant mass of the lepton from the $W$-boson decay $\ell$ (with $\ell=e,\mu$) and of the soft muon $\mu$ originated by the $b$-hadron decay, $m_{\ell\mu}$, is reconstructed in data and a template fit is performed to extract $m_t$. The measured value of the top quark mass is $m_t = 174.48 \pm 0.78(stat.+syst.)$ GeV based on a data collected during 2015+2016 Run2 campaign corresponding to an integrated luminoisty of 36.1 fb$^{-1}$.