CMS-PAS-TOP-14-011

CMS-PAS-TOP-14-011
Measurement of the top-quark mass using the BEST-assisted $R$ distribution in the $\mu$+jets channel
CMS Collaboration
November 2015

Abstract: 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 (stat) $\pm$ 0.90 (syst) GeV, in agreement with previous measurements.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Summary	CMS Publications

Summary

The top-quark mass is measured using the template method based on the mass ratio R of the reconstructed top quark and Wboson from three jets and two jets, respectively. The shapes of the combinatorial backgrounds for the trijet and dijet invariant mass distributions are modelled by BEST. The analysis is performed in the muon plus jets channel using the data sample collected by CMS which corresponds to an integrated luminosity of 19.7 fb$^{-1}$ from proton?proton collisions at a centre-of-mass energy of 8 TeV. The result from the fit to the distribution of R when performed on the observed data is $m_{\mathrm{t}} =$ 172.61 $\pm$ 0.57 (stat) $\pm$ 0.90 (syst) GeV, corresponding to a precision of 0.62%.
Since event mixing is novel to estimate $ \mathrm{ t \bar{t} }$ events, the BEST method is successfully applied for the modelling of the main background in the invariant mass distribution of the selected jet pairs and triplets. Given the final uncertainty obtained for the measurement of the top-quark mass, after a careful choice of the variable which minimizes the main uncertainty, we believe that this demonstrates the feasibility of applying the method for an analysis of a model-independent search for new hadronically-decaying resonances which may be found in the future.