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

Author(s): Sirunyan, AM; Tumasyan, A; Adam, W; Ambrogi, F; Bergauer, T; Dragicevic, M; Ero, J; Escalante Del Valle, A; Flechl, M; Fruhwirth, R; Jeitler, M; Krammer, N; Kratschmer, I; Liko, D; Madlener, T; Mikulec, I; Rad, N; Schieck, J; Schofbeck, R; Spanring, M; Waltenberger, W; Wulz, CE; Zarucki, M; Drugakov, V; Mossolov, V; Suarez Gonzalez, J; Darwish, MR; De Wolf, EA; Di Croce, D; Janssen, X; Kello, T; Lelek, A; Pieters, M; Rejeb Sfar, H; Van Haevermaet, H; Van Mechelen, P; Van Putte, S; Van Remortel, N; Blekman, F; Bols, ES; Chhibra, SS; D'Hondt, J; De Clercq, J; Lontkovskyi, D; Lowette, S; Marchesini, I; Moortgat, S; Python, Q; Tavernier, S; Van Doninck, W; Van Mulders, P; Beghin, D; Bilin, B; Clerbaux, B; De Lentdecker, G; Delannoy, H; Dorney, B; Favart, L; Grebenyuk, A; Kalsi, AK; Moureaux, L; Popov, A; Postiau, N; Starling, E; Thomas, L; Vander Velde, C; Vanlaer, P; Vannerom, D; Cornelis, T; Dobur, D; Khvastunov, I; Niedziela, M; Roskas, C; Skovpen, K; Tytgat, M; Verbeke, W; Vermassen, B; Vit, M; Bruno, G; Caputo, C; David, P; Delaere, C; Delcourt, M; Giammanco, A; Lemaitre, V | Abstract: The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |η|Vtb, |η|Vtd, and |η|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 |η|Vtbg0.970 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|Vtb=0.988±0.024, and |η|Vtd2+|η|Vts2=0.06±0.06, where the uncertainties include both statistical and systematic components, are measured.