Prospects for $B_c^{+}\to {\tau }^{+}{\nu }_{\tau }$ at FCC-ee

Abstract

This paper presents the prospects for a precise measurement of the branching fraction of the leptonic $B_c^{+}\to {\tau }^{+}{\nu }_{\tau }$ 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 $b\bar{b}$, $c\bar{c}$, and $q\bar{q}$ backgrounds using event-based topological information. A second stage utilises the properties of the hadronic ${\tau }^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\bar{\nu }}_{\tau }$ decay to further suppress these backgrounds, and is also found to achieve high rejection for the $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ background. The number of $B_c^{+}\to {\tau }^{+}{\nu }_{\tau }$ 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.

arXiv comment31 pages, 11 figures

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