Signatures of light new particles in B→K(*)Emiss

Abstract

The recent Belle II observation of B→KEmiss challenges theoretical interpretations in terms of Standard Model neutrino final states. Instead, we consider new physics scenarios where up to two new light-invisible particles of spin 0 up to 3/2 are present in the final state. We identify viable scenarios by reconstructing the (binned) likelihoods of the relevant B→K(*)Emiss and also Bs→Emiss experimental analyses and present preferred regions of couplings and masses. In particular, we find that the current data prefer two-body decay kinematics involving the emission of a single massive scalar or a vector particle or, alternatively, three-body decays involving pairs of massive scalars or spin 1/2 fermions. When applicable, we compare our findings with existing literature and briefly discuss some model-building implications. Published by the American Physical Society 2024