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|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 |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.
Highlights
A distinctive feature of the electroweak sector of top quark physics is the relative magnitude of the Cabibbo–Kobayashi– Maskawa (CKM) [1] matrix element V tb with respect to V td and V ts, which leads to a strong suppression of processes involving mixing between the third and the first two quark families
The three CKM matrix elements are extracted by measuring the production cross sections and branching fractions of single top quark t-channel processes that depend on V tb, V td, and V ts in production and decay
A measurement of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |V tb |, |V td |, and |V ts | has been performed in an event sample enriched in t-channel single top quark events, featuring one muon or electron and je√ts in the final state
Summary
A distinctive feature of the electroweak sector of top quark physics is the relative magnitude of the Cabibbo–Kobayashi– Maskawa (CKM) [1] matrix element V tb with respect to V td and V ts , which leads to a strong suppression of processes involving mixing between the third and the first two quark families. This feature can be probed at the CERN LHC by studying the couplings of top quarks to d, s, and b quarks in electroweak charged-current interactions, where such couplings play a role at either the production or decay vertices of the top quark. We present the first direct and model-independent simultaneous measurement of |V tb |, |V td |, and |V ts |, by considering their respective contributions to the top quark t-channel production and decay
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