Prospects for B-c(+) -> tau(+)nu(tau) at FCC-ee

This paper presents the prospects for a precise measurement of the branching fraction of the leptonic B-c(+) -> tau(+)nu(tau) decay at the Future Circular Collider (FCC-ee) running at the Z-pole. A detailed description of the simulation and analysis framework is provided. To select signal candidates, two Boosted Decision Tree algorithms are employed and optimised. The first stage suppresses inclusive b (b) over bar, c (c) over bar, and q (q) over bar backgrounds using event-based topological information. A second stage utilises the properties of the hadronic tau(+)-> pi(+)pi(+)pi(-)(nu) over bar (tau) decay to further suppress these backgrounds, and is also found to achieve high rejection for the B+-> tau(+)nu(tau) background. The number of B+-> tau(+)nu(tau) candidates is estimated for various Tera-Z scenarios, and the potential precision of signal yield and branching fraction measurements evaluated. The phenomenological impact of such measurements on various New Physics scenarios is also explored.