Asymmetry observables and the origin of RD (∗) anomalies

Abstract

The RD(∗) anomalies are among the longest-standing and most statistically significant hints of physics beyond the standard model. Many models have been proposed to explain these anomalies, including the interesting possibility that right-handed neutrinos could be involved in the B decays. In this paper, we investigate future measurements at Belle II that can be used to tell apart the various new physics scenarios. Focusing on a number of τ asymmetry observables (forward-backward asymmetry and polarization asymmetries) which can be reconstructed at Belle II, we calculate the contribution of the most general dimension 6 effective Hamiltonian (including right-handed neutrinos) to all of these asymmetries. We show that Belle II can use these asymmetries to distinguish between new-physics scenarios that use right- and left-handed neutrinos, and in most cases can likely distinguish the specific model itself.