Determining the photon polarization of the b --> s gamma using the B --> K1(1270) gamma --> (K pi pi) gamma decay

Understand

Recently the radiative B decay to the strange axial-vector mesons, B --> K1(1270) gamma, has been observed with rather large branching ratio.

• This process is particularly interesting as the subsequent K1 decay into its three body final state allows us to determine the polarization of the photon, which is mostly left- (right-)handed for Bbar (B) in the SM while various new physics models predict additional right- (left-)handed components.
• A new method is proposed to determine the polarization, exploiting the full Dalitz plot distribution, which seems to reduce significantly the statistical errors.
• This polarization measurement requires however a detailed knowledge of the K1--> K pi pi strong interaction decays, namely, the various partial wave amplitudes into the several possible quasi two-body channels, as well as their relative phases.