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 |η|V_tb, |η|V_td, and |η|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 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 |η|V_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 |η|V_tb=0.988±0.024, and |η|V_td ²+|η|V_ts ²=0.06±0.06, where the uncertainties include both statistical and systematic components, are measured.