Parity doubling as a tool for right-handed current searches

The V-A structure of the weak interactions leads to definite amplitude hierarchies in exclusive heavy-to-light decays mediated by b → (d, s)γ and $$ b\to \left(d,\ s\right)\ell \overline{\ell} $$ . However, the extraction of right-handed currents beyond the Standard Model is contaminated by V-A long-distance contributions leaking into right-handed amplitudes. We propose that these quantum-number changing long-distance contributions can be controlled by considering the almost parity-degenerate vector meson final states by exploiting the opposite relative sign of left- versus right-handed amplitudes. For example, measuring the time-dependent rates of a pair of vector V (J P = 1−) and axial A(1+) mesons in B → (V, A)γ, up to an order of magnitude is gained on the theory uncertainty prediction, controlled by long-distance ratios to the right-handed amplitude. This renders these decays clean probes to null tests, from the theory side.