Effects of a fourth family on b-->s[gamma] and a useful parametrization of quark mixing for rare B decays

Abstract

The effects of a fourth family on the decays b-->s(d)[gamma] are reported. The BR(b-->s[gamma]) can become ~10-3, i.e., a gain from the three-generation result by an order of magnitude. For very massive t' (mt > 200GeV) the four-generation result is not sensitive to mt, making the reaction usuful for probing the new mixing angles of the fourth generation. We emphasize that combined information from b-->s[gamma], sl+l- and the hadronic b-->s transition without charmed particles would be useful for constraining mass scales and mixing parameters of a fourth generation. In view of the importance of B decays we present a new parametrization of the 4 x 4 mixing matrix that appears to be better suited for the study of B physics.