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

The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |V$_{tb}$|, |V$_{td}$|, and |V$_{ts}$|, 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 13TeV, corresponding to an integrated luminosity of 35.9fb$^{-1}$. 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$_{tb}$| >0.970is 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$_{tb}$| =0.988 ±0.024, and |V$_{td}$|2+|V$_{ts}$|2=0.06 ±0.06, where the uncertainties include both statistical and systematic components, are measured.