Abstract:

is a Flavor Changing Neutral Current (FCNC) process which is highly suppressed at the tree level in the Standard Model by the GIM mechanism. However, the large violation of the quark mass equality by the top quark allows this decay to proceed very slowly at the loop level with a branching ratio of the order of , making this decay very sensitive to the CKM matrix element . Measurement of from this decay will put additional constraint on the CKM triangle and since the theoretical uncertainty for this decay is very small, a precise measurement of this branching ratio will be a test of SM. The experimental search for this decay has been extended to a new region in the pion momentum spectrum. Recent results from BNL E787/E949 will be presented in this talk.