H E

Radiative penguin decays ofB mesons are avour-changing neutral current (FCNC) processes, studies of which provide fertile ground for precision tests of the Stan-dard Model. Because such decays must proceed through 1-loop or higher order processes, they are rare and their amplitudes are particularly sensitive to inter-ference from other FCNC interactions beyond the SM. This thesis presents the search for the rare radiative penguin process b! d , carried out at the BABAR experiment. This inclusive decay has yet to be observed, with this analysis mea-suring the branching fraction to 3.1 signicance as (2:47 0:72+0:420:44) 105, where the rst error is statistical and the second systematic. 90 % condence limits are set on its branching fraction: 1:4 105 < BF (b! d ) < 3:6 105. As a cross-check of the experimental procedure, measurements of the branching fraction and the direct CP violation of the exclusive b! s decay B! K are made, with BF (B! K ) = (3:74 0:16 0:41) 105 and ACP (B! K ) = 0:0790:0360:001. This analysis also measures the branching fraction and di-rect CP asymmetry of the b! s decay: BF (b! s ) = (3:540:190:39)104 and ACP (b! s ) = 0:040 0:035 0:004. The branching fraction of the exclu-sive b! d decays B! (;!) is also measured as a cross-check, and found to be BF (B! (;!) ) = (1:46 0:59+0:180:19) 106. All measurements made with control samples are found to be consistent with recent published experimental results and theoretical predictions. Finally, the ratio of the branching fractions b! d and b! s is used to set a bound on the CKM matrix element ratio 0:17 < jVtd Vts j < 0:43 at 90 % condence level. Combining this with the ratio ob-tained from the cross-check B! K and B! (;!) control samples gives 0:15 < jVt