Measuring the photon polarization in b->s gamma using the B-> K*e+e- decay channel

The decay B0 -> K* e+e- proceeds via electroweak penguin and box diagrams. The low e+ e- mass region is dominated by the photon term and an analysis of the angular variables allows to test the photon helicity which is expected to be predominantly left-handed. For an integrated luminosity of 2 fb-1 the expected accuracy on the fraction of wrongly polarized photons is of the order of 0.1 assuming a background over signal ratio of 1.