Measurement of CKM matrix elements in single top quark t-channel production in proton-proton collisions at √s = 13 TeV

Abstract

The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |Vtb |, |Vtd |, and |Vts |, 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 |Vtb | > 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 |Vtb | = 0.988 ± 0.024, and |Vtd | 2 + |Vts | 2 = 0.06 ± 0.06, where the uncertainties include both statistical and systematic components, are measured.