Measurement of CKM element |Vcb| from W boson decays at the future Higgs factories

A bstract This study investigates the precision measurement of the CKM matrix element | V cb | through semileptonic WW events at future Higgs factories, i.e., FCC-ee, ILC, C 3 , and CEPC. We use full detector simulation to generate the WW → ℓνcb signal events and various backgrounds at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 240 GeV with unpolarized beams. The relative statistical uncertainties of | V cb | are projected to be 0.91% for the muon channel and 1.2% for the electron channel, assuming a baseline integrated luminosity of 5 ab −1 . The sensitivities at other Higgs factory scenarios are also projected. Possible contributors to systematic uncertainties are discussed, with the most prominent one being the systematics of flavor-tagging and mistagging rates. Combining with WW threshold runs, the relative systematic uncertainty can be further reduced.