PoS - Proceedings of Science
Volume 397 - The Ninth Annual Conference on Large Hadron Collider Physics (LHCP2021) - Top physics
Single Top Measurement Highlights at CMS
M. Kumar
Full text: pdf
Pre-published on: October 20, 2021
Published on: November 17, 2021
The $\it{t}$-channel and $\mathrm{tW}$-channel are the two most dominant single top quark production processes at the LHC.
These processes provide a unique phase space at lower interaction scale with lower colour reconnection probability compared to the top quark pair production.
The $\it{t}$-channel ($\mathrm{tW}$-channel) final state comprises a single top quark produced along with a light quark (W boson) leading to at least two (three) jets, one of which arises from the hadronization of a b-quark, an isolated energetic lepton (electron or muon), and large missing momentum due to a neutrino escaping from the W boson decay. In this report, measurements of the top quark mass in single top $\it{t}$-channel process and of the production cross-section in $\mathrm{tW}$-channel are reported based on $35.9\,{\rm fb}^{-1}$ of proton-proton (pp) collision data recorded at 13\,TeV by the CMS experiment during 2016.
A multivariate technique relying on boosted decision trees is deployed to optimally separate signal from background in both measurements. A simultaneous maximum-likelihood fit has been performed in electron and muon final states.
The response of the boosted decision trees has been used in a binned likelihood fit to extract the $\mathrm{tW}$-channel cross-section. The measured signal strength and cross section are $1.24 \pm 0.18$ and $89 \pm 4$ (stat) $\pm 12$ (syst) pb, respectively. Whereas the top quark mass is obtained by fitting its reconstructed mass distribution using a suitable combination of parametric shapes to model the $\it{t}$-channel signal and various backgrounds. The measured mass of the top quark is found to be $172.13^{+0.76}_{ - 0.77}$ GeV, reaching a sub-GeV precision for the first time in this specific phase space. The top quark to top antiquark mass ratio and difference are also calculated using the separately measured top and top antiquark mass depending on the lepton charge in the final state. The calculated mass ratio and difference are $0.9952^{+0.0079}_{-0.0104}$ and $0.83^{+1.79}_{-1.35}$ GeV.
DOI: https://doi.org/10.22323/1.397.0307
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