Abstract
The decay B^0_srightarrow mu ^+mu ^- is a key probe for the search of physics beyond the Standard Model. While the current measurements of the corresponding branching ratio agree with the Standard Model within the uncertainties, significant New-Physics effects may still be hiding in B^0_srightarrow mu ^+mu ^-. In order to reveal them, the observable mathcal {A}^{mu mu }_{Delta Gamma _s}, which is provided by the decay width difference Delta Gamma _s of the B^0_s-meson system, plays a central role. We point out that a measurement of a CP-violating observable mathcal{S}_mathrm{mu mu }, which is induced through interference between B^0_s–{bar{B}}^0_s mixing and B_srightarrow mu ^+mu ^- decay processes, is essential to obtain the full picture, in particular to establish new scalar contributions and CP-violating phases. We illustrate these findings with future scenarios for the upgrade(s) of the LHC, exploiting also relations which emerge within an effective field theory description of the Standard Model, complemented with New Physics entering significantly beyond the electroweak scale.
Highlights
The decay Bs0 → μ+μ− is one of the most interesting processes offered by Nature, allowing us to test the Standard Model (SM) and probe New Physics (NP)
The theoretical framework to describe the decay Bs0 → μ+μ− is given by effective quantum field theory, which allows the calculation of a low-energy effective Hamiltonian of the following general structure [1,5,7]: Heff
The rare decay Bs0 → μ+μ− has been in the focus of particle physics for decades, offering one of the theoretically cleanest probes for physics beyond the SM, in particular for new-scalar contributions, which are still largely unconstrained
Summary
The decay Bs0 → μ+μ− is one of the most interesting processes offered by Nature, allowing us to test the Standard Model (SM) and probe New Physics (NP). The SM branching ratio is enormously suppressed, and only about three out of one billion Bs0 mesons decay into the μ+μ− final state. Another key feature of Bs0 → μ+μ− is related to the impact of strong interactions. In these observables, as in the case of Aμμ , the decay cons stant fBs cancels. As in the case of Aμμ , the decay cons stant fBs cancels In analyses of rare B(s) decays, it is usually – for simplicity – assumed that CP-violating NP phases vanish Within specific models, such assumptions can be made, where an important example is given by scenarios with “Minimal Flavour
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