Measurement of the top-quark mass using the BEST-assisted $R$ distribution in the muon + jets channel

A measurement of the top-quark mass is presented using a template method based on the Bi-Event Subtraction Technique (BEST). Top-quark-pair candidate events with one muon and at least four jets in the final state are selected in proton--proton collision data recorded by the CMS experiment in 2012. The dataset corresponds to an integrated luminosity of 19.7 fb$^{-1}$. The top-quark mass is extracted from the distribution of the ratio $R$ of three-jet and two-jet invariant-mass combinations, corresponding to the top-quark and W boson candidate masses, respectively. The BEST method is used to determine the shape of the background distribution. By taking the ratio, a significant reduction of the dominant systematic uncertainty associated to the jet energy scale is achieved. The top-quark mass is measured to be $m_t = 172.61 \pm 0.57~(\rm stat.) \pm 0.90~(\rm syst.)$ GeV, in agreement with previous measurements.