New Physics in Bq 0Bq 0 mixing: Present challenges, prospects, and implications for Bq 0→μ+μ-

The phenomenon of Bq0Bq0 mixing (q=d,s) provides a sensitive probe for physics beyond the Standard Model. We explore the corresponding space for New Physics left through the current data, having a careful look at analyses of the Unitarity Triangle that are needed for the Standard Model predictions of the Bq mixing parameters. In particular, we explore the impact of tensions between inclusive and exclusive determinations of the CKM matrix elements |Vub| and |Vcb|. Moreover, we focus on the angle γ of the Unitarity Triangle, comparing measurements from B→DK and B→ππ, ρπ, ρρ decays, where the latter are typically interpreted in terms of the angle α. We discuss various scenarios and present the corresponding state-of-the-art constraints on the New Physics parameters of Bq0Bq0 mixing. We point out that these results have an interesting application in the analysis of rare Bq0→μ+μ- decays, allowing us to minimise the impact of CKM parameters in the search for New Physics. In view of the high-precision era, we make future projections. Interestingly, we find that for the extraction of the New Physics parameters in the Bd system the determination of the apex of the Unitarity Triangle results in a key limiting factor. By contrast, the corresponding impact is negligible for the Bs system, making it a promising candidate to reveal sources of New Physics.