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.