Measurement of CKM matrix elements in single top quark $t$-channel production in proton-proton collisions at $\sqrt{s}=$ 13 TeV

Abstract

The first direct, model-independent measurement is presented of the modulus of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{\mathrm{tb}}|$, $|V_{\mathrm{td}}|$, and $|V_{\mathrm{ts}}|$, in final states enriched in single top quark $t$-channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb${}^{-1}$. Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of $|V_{\mathrm{tb}}|$ $>$ 0.970 is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values $|V_{\mathrm{tb}}|=$ 0.988 $\pm$ 0.024, and $|V_{\mathrm{td}}{|}^2+|V_{\mathrm{ts}}{|}^2=$ 0.06 $\pm$ 0.06, where the uncertainties include both statistical and systematic components, are measured.

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/TOP-17-012 (CMS Public Pages)

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