Measurement of the Vcb element in top-quark pair events in CMS

Measurements of the CKM matrix element Vcb are presented using proton–proton collision data collected with the CMS detector during the LHC Run 2 and Run 3 periods. The measurements exploit top-quark pair events in which one top quark decays via a W boson to a final state with an electron or a muon and neutrinos, and the other top quark decays via a W boson to a charm quark and a bottom quark. The analyses rely on dedicated CMS jet-flavor tagging algorithms to efficiently and precisely identify jets originating from charm and bottom quarks. Binned maximum-likelihood fits are performed to extract the branching fraction of the decay of a W boson to a charm quark and a bottom quark. This measurement is then used to infer the magnitude of the CKM matrix element Vcb, providing a direct determination of this fundamental parameter from top-quark events.