CMS-TOP-17-012
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 |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.