Precision measurement of the top quark mass with single top events at CMS

A measurement of the top quark mass in single top events produced in the $t$-channel at the CMS experiment is presented. The $t$-channel is the dominant process for single top quark production at the LHC. The $t$-channel process provides a unique phase space with different color reconnection conditions than that of $\mathrm{t}\bar{\mathrm{t}}$ events, which are are exploited for the most precise measurements of the top-quark mass. . The final state comprises a single top quark along with a light quark giving rise to at least two jets, (one of which arises from the hadronization of a b quark), an isolated high-momentum lepton (electron or muon), and large missing transverse momentum due to an escaping neutrino from the W boson decay. The study is based on proton-proton collision data, equivalent to $35.9$ $\mathrm{fb}^{-1}$ integrated luminosity, recorded at $\sqrt{s}$ = 13 TeV by the CMS experiment during 2016. Dominant standard model backgrounds are studied in different kinematic regions depending on the number of b-tagged quarks and light-flavor jets in the final state. A multivariate technique relying on boosted decision trees is employed to optimally separate the signal from backgrounds. The top-quark mass is reconstructed using kinematic information of the final-state objects, namely the charged lepton, missing transverse momentum, and jets. We obtain the top quark mass $m_\mathrm{t}=172.13^{+0.69}_{-0.70}$ GeV, by fitting the reconstructed mass distribution using an appropriate combination of parametric shapes.