RESUMEN
Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.
RESUMEN
Motivated by the recent evidence for B+âK+ν¯ν decays at Belle II, we point out that fully invisible Bd and Bs meson decays are strongly constrained by LEP. A reinterpretation of an old inclusive ALEPH search for b-hadron decays with large missing energy allows us to place the limits Br(Bdâinvisible)<1.4×10-4 and Br(Bsâinvisible)<5.6×10-4, both at 90% CL. The Bd limit is only a factor of 6 looser than the world-leading one provided by the BaBar collaboration, while the Bs one is the first limit in the literature on this decay mode. These results are relevant in the context of new light states coupled to quarks and exemplify the power of a future Tera-Z factory at FCC-ee to look for B meson decays containing missing energy.