Springer : Prospects for $B_c^+$ and $B^+\rightarrow \tau ^+ \nu _\tau $ at FCC-ee

Zuo, Xunwu; Hill, Donal; Klute, Markus; Iguro, Syuhei; Helsens, Clément; Fedele, Marco

doi:10.1140/epjc/s10052-024-12418-0

Article
Report number	arXiv:2305.02998 ; TTP23-015 ; P3H-23-28
Title	Prospects for $B_c^+$ and $B^+\rightarrow \tau ^+ \nu _\tau $ at FCC-ee
Author(s)	Zuo, Xunwu (KIT, Karlsruhe, ETP) ; Fedele, Marco (KIT, Karlsruhe, TTP) ; Helsens, Clément (KIT, Karlsruhe ; Ecole Polytechnique, Lausanne ; CERN) ; Hill, Donal (Ecole Polytechnique, Lausanne) ; Iguro, Syuhei (KIT, Karlsruhe, TTP ; KIT, Karlsruhe, IAP) ; Klute, Markus (KIT, Karlsruhe)
Publication	2024-01-26
Imprint	2023-05-04
Number of pages	28
Note	39 pages, 19 figures, 5 tables
In:	Eur. Phys. J. C 84 (2024) 87
DOI	10.1140/epjc/s10052-024-12418-0
Subject category	hep-ph ; Particle Physics - Phenomenology ; hep-ex ; Particle Physics - Experiment
Study	CERN FCC
Abstract	The prospects are presented for precise measurements of the branching ratios of the purely leptonic $B_c^+ \to \tau^+ \nu_\tau$ and $B^+ \to \tau^+ \nu_\tau$ decays at the Future Circular Collider (FCC). This work is focused on the hadronic $\tau^{+} \to \pi^+ \pi^+ \pi^- \bar{\nu}_\tau$ decay in both $B_c^+ \to \tau^+ \nu_\tau$ and $B^+ \to \tau^+ \nu_\tau$ 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 $B^+ \to \tau^+ \nu_\tau$ decay can be well separated from both $B_c^+ \to \tau^+ \nu_\tau$ and generic $Z\to b\bar{b}$ 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 $B^+ \to \tau^+ \nu_\tau$ and $B_c^+ \to \tau^+ \nu_\tau$ measurements on New Physics cases are discussed for interpretations in the generic Two-Higgs-doublet model and leptoquark models.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2024-2025 The Author(s) (License: CC-BY-4.0)