Measurement of CKM matrix element |Vcb| in ttbar events with the ATLAS detector
by
Small Lecture Theatre
Poynting
The top quark is a unique probe for physics in the Standard Model and beyond. This talk highlights recent ATLAS results on free parameter measurements using top quark events. In particular, we focus on the first measurement of the CKM matrix element |Vcb| using on-shell W-boson decays in ttbar events. This analysis offers an independent test of the long-standing tension in traditional low-energy extractions via inclusive and exclusive semileptonic decays of B hadrons. Using 140 fb-1 of pp collision data at 13 TeV collected by the ATLAS experiment during Run 2, a value of |Vcb| = (50 +11/-14) x 10^-3 is obtained, with roughly equal statistical and systematic uncertainties. While the sensitivity does not yet rival traditional determinations made at much lower energy scales, this novel approach probes a completely different physical situation, namely the rare hadronic t -> b bbar c decay at high momentum-transfer. Together, these analyses demonstrate innovative ways to leverage vast LHC datasets to push the precision frontier and explore rare processes.