A model-independent extraction of the modulus of the Cabibbo– Kobayashi–Maskawa matrix elements Vtb, Vtd, and Vts, is presented for the first time using an event sample enriched in single top quark t-channel events. The analysis uses proton-proton collisions data from the LHC, collected during 2016 with 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 the matrix elements Vtb, Vtd, and Vts are considered in both the production and decay vertices of the top quark in single top quark t-channel production, as well as in the background processes containing top quarks. In the standard model hypothesis of CKM unitarity, a lower limit of |Vtb| > 0.971 is measured at the 95% confidence level. Several beyond-the standard model possibilities are considered, and by releasing all constraints between the involved parameters, the values |Vtb| = 0.988 ± 0.024, and |Vtd|2 + |Vts|2 = 0.06 ± 0.06 are measured.
Michelangelo Mangano, Monica Pepe-Altarelli and Guillaume Unal