S. Recksiegel

The purely leptonic decays D -> e nu and Ds -> e nu, for which no experimental limits exist, are highly suppressed in the Standard Model. Mere observation of these decays at the B factories BELLE/BaBar or forthcoming CLEO-c would be a clear signal of physics beyond the SM. We show that R parity violating slepton contributions can give rise to spectacular enhancements of the decay rates, resulting in branching ratios as large as 5 x 10^-3, which strongly motivates a search in these channels.

High Luminosity upgrades of the KEK-B collider are being discussed. We consider the role of the purely leptonic decays B^\pm -> l^\pm nu and B^0 -> l+l- in motivating such an upgrade. These decays are very sensitive to R parity violating extensions of the MSSM, and we show that future runs of the KEK-B factory can be competitive with high energy colliders for probing such models.

We study the decays Bu -> l nu and Bc -> l nu in the context of the Minimal Supersymmetric Standard Model (MSSM) with explicit R parity violation. We analyse the correlation between the two decays and show that branching ratios (BRs) for Bc -> l nu may be of order 5% (over 40% in one case), without violating current bounds on Bu -> l nu. Although Bc mesons are inaccessible at the e+e- B factories, such large BRs for Bc -> l nu would possibly be within experimental observability at LEP and the Tevatron Run II, with much larger yields expected at the hadronic B factories. We also update some earlier bounds on products of R parity violating couplings in the light of new experimental results.

We investigate the effect of vector quarks on the inclusive decays B -> X_d,s \gamma. We show that the branching ratio of B -> X_d \gamma can differ sizably from the SM and MSSM predictions, being enhanced to present experimental observability or suppressed such that present runs of the B factories would not observe it. Current measurements of the direct CP asymmetry (A_CP) for B -> X_s \gamma are sensitive to the contribution from B -> X_d \gamma. For a sufficiently enhanced BR(B -> X_d \gamma) we show that the dominant contribution to the combined asymmetry may be from B -> X_d \gamma. Thus any large value for A_CP should not immediately be attributed to B -> X_s \gamma, which stresses the importance of good K/pi separation.

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B\to X_d\gamma. Although such a decay contains a large background from B\to X_s\gamma, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A_CP) lies in the region -40% \le A_CP \le 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B\to X_d\gamma proves too dif ficult experimentally, its asymmetry contributes non-negligibly to the measurements of A_CP for B\to X_s\gamma, and thus should be included in future analyses. We show t hat there may be both constructive and destructive interference between A^d\gamma_CP and A^s\gamma_CP.

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B\to X_d\gamma. Although such a decay contains a large background from B\to X_s\gamma, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A_CP) lies in the region -40% \le A_CP \le 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B\to X_d\gamma proves too dif ficult experimentally, its asymmetry contributes non-negligibly to the measurements of A_CP for B\to X_s\gamma, and thus should be included in future analyses. We show t hat there may be both constructive and destructive interference between A^d\gamma_CP and A^s\gamma_CP.