Time-Dependent Precision Measurement of $B_s^0\rightarrow ϕμ^+μ^-$ Decay at FCC-$ee$
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2025
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| _version_ | 1866913886995742720 |
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| author | Kwok, Tsz Hong Polonsky, Zachary Lukashenko, Valeriia Aebischer, Jason Kilminster, Ben |
| author_facet | Kwok, Tsz Hong Polonsky, Zachary Lukashenko, Valeriia Aebischer, Jason Kilminster, Ben |
| contents | We study the feasibility of measuring time-dependent $C\!P$ violation in the rare flavor-changing neutral current (FCNC) decay $B_s^0 \rightarrow ϕ(\rightarrow K^+K^-) μ^+ μ^-$ at the FCC-$ee$. In the Standard Model (SM), $C\!P$ violation in this mode arises only at higher orders and is highly suppressed. Extensions of the SM, collectively referred to as New Physics (NP), can introduce additional $C\!P$-violating phases that enhance such effects. The decay $B_s^0 \rightarrow ϕμ^+ μ^-$, mediated by the $b \rightarrow s \ell^+ \ell^-$ transition, is therefore a promising probe of NP. The FCC-$ee$, operating as a high-luminosity $Z$-factory, offers an optimal environment for this measurement due to its large event yield, clean conditions, efficient particle identification, and excellent vertex resolution. We perform a Monte Carlo study using Pythia and Delphes with the IDEA detector concept. A relative precision better than $\mathcal{O}(1\%)$ on the branching ratio and $\mathcal{O}(10^{-2})$ on the time-integrated $C\!P$ asymmetry is found to be achievable. We determine the projected sensitivities to the observables $D_f$, $C_f$, and $S_f$, which parameterize time-dependent $C\!P$ violation. In the untagged analysis, a precision of $\mathcal{O}(10^{-1})$ on $D_f$ can be reached. With flavor tagging, sensitivities to $C_f$ and $S_f$ improve to $\mathcal{O}(10^{-2})$. These measurements remain inaccessible to current flavor experiments. Interpreting the results within the Weak Effective Theory provides model-independent constraints on $C\!P$-violating NP. This study demonstrates that FCC-$ee$ enables first-time access to $C\!P$-sensitive observables previously beyond experimental reach. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_08089 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Time-Dependent Precision Measurement of $B_s^0\rightarrow ϕμ^+μ^-$ Decay at FCC-$ee$ Kwok, Tsz Hong Polonsky, Zachary Lukashenko, Valeriia Aebischer, Jason Kilminster, Ben High Energy Physics - Phenomenology High Energy Physics - Experiment We study the feasibility of measuring time-dependent $C\!P$ violation in the rare flavor-changing neutral current (FCNC) decay $B_s^0 \rightarrow ϕ(\rightarrow K^+K^-) μ^+ μ^-$ at the FCC-$ee$. In the Standard Model (SM), $C\!P$ violation in this mode arises only at higher orders and is highly suppressed. Extensions of the SM, collectively referred to as New Physics (NP), can introduce additional $C\!P$-violating phases that enhance such effects. The decay $B_s^0 \rightarrow ϕμ^+ μ^-$, mediated by the $b \rightarrow s \ell^+ \ell^-$ transition, is therefore a promising probe of NP. The FCC-$ee$, operating as a high-luminosity $Z$-factory, offers an optimal environment for this measurement due to its large event yield, clean conditions, efficient particle identification, and excellent vertex resolution. We perform a Monte Carlo study using Pythia and Delphes with the IDEA detector concept. A relative precision better than $\mathcal{O}(1\%)$ on the branching ratio and $\mathcal{O}(10^{-2})$ on the time-integrated $C\!P$ asymmetry is found to be achievable. We determine the projected sensitivities to the observables $D_f$, $C_f$, and $S_f$, which parameterize time-dependent $C\!P$ violation. In the untagged analysis, a precision of $\mathcal{O}(10^{-1})$ on $D_f$ can be reached. With flavor tagging, sensitivities to $C_f$ and $S_f$ improve to $\mathcal{O}(10^{-2})$. These measurements remain inaccessible to current flavor experiments. Interpreting the results within the Weak Effective Theory provides model-independent constraints on $C\!P$-violating NP. This study demonstrates that FCC-$ee$ enables first-time access to $C\!P$-sensitive observables previously beyond experimental reach. |
| title | Time-Dependent Precision Measurement of $B_s^0\rightarrow ϕμ^+μ^-$ Decay at FCC-$ee$ |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2506.08089 |