On the S-wave pollution of B→K ^*l+ ^l- observables

It has been argued recently that transverse asymmetries that are expected to be shielded from the presence of the S-wave Kπ pairs originating from the decay of a scalar K0* meson, are indeed affected by this pollution due to the impossibility to extract cleanly the normalization for these observables. In this short article we show how using folded distributions, which is nowadays the preferred method to obtain the information from the 4-body decay mode B→K *(→Kπ)l +l -, one can easily bypass this problem and extract the clean observables P 1,2,3 and also P4,5,6′ in a way completely free from this pollution including all lepton mass corrections. We also show that in case one insists in using uniangular distributions to extract these observables, it is possible to reduce this pollution to just lepton mass suppressed terms. On the contrary, the S i observables, that are by definition normalized by the full differential decay distribution, will indeed suffer from this pollution via their normalization. Finally, we also present a procedure to minimize the error associated to neglecting lepton mass corrections in the distribution defining a massless-improved limit. © 2012 American Physical Society.