Prospects for Bc+ and B+ → Τ+ντ at FCC-ee

The prospects are presented for precise measurements of the branching ratios of the purely leptonic B-c(+) -> tau(+)nu(tau) and B+ -> tau(+)nu(tau) decays at the Future Circular Collider (FCC). This work is focused on the hadronic tau(+) -> pi(+)pi(+)pi (-) nu(tau) decay in both B-c(+) -> tau(+)nu(tau) and B+ -> tau (+)nu(tau) processes. Events are selected with two Boosted Decision Tree algorithms to optimise the separation between the two signal processes as well as the generic hadronic Z decay backgrounds. The range of the expected precision for both signals are evaluated in different scenarios of non-ideal background modelling. This paper demonstrates, for the first time, that the B+ -> tau(+)nu(tau) decay can be well separated from both B-c(+) -> tau(+)nu(tau) and generic Z -> bb processes in the FCC-ee collision environment and proposes the corresponding branching ratio measurement as a novel way to determine the CKM matrix element |V-ub|. The theoretical impacts of both B+ -> tau(+)nu(tau) and B-c(+) -> tau(+)nu(tau) measurements on New Physics cases are discussed for interpretations in the generic Two-Higgs-doublet model and leptoquark models.