Flavour-changing neutral current decays of heavy baryons. The case

Abstract

We investigate the rare decay b ! fl which receives both short and long distance contributions. We estimate the long distance contributions and find them very small. The form factors are obtained from c ! ` ¯ ` using heavy quark symmetry and a pole model. The short distance piece opens a window to new physics and we discuss the sensitivity of b ! fl to such effects. 1 Introduction Flavour Changing Neutral Current (FCNC) processes have attracted renewed attention since the recent CLEO measurement of the FCNC decays of the type b ! sfl. In the Standard Model (SM) these processes are forbidden at the tree level and are strongly suppressed by the GIM mechanism, in particular for up type quarks. Hence they offer a unique possibility to test the CKM sector of the SM and possibly open a window to physics beyond the SM. From the experimental side there is some data on the exclusive decay B ! K fl and the inclusive decay B ! X s fl with branching fractions [1] Br(B + ! K + fl) =...