This PhD thesis presents the exclusive radiative decays of B meson within the Standard Model (SM). In particular, we consider the decays Bâ†’Î³â„“vâ„“ and Bâ†’ (K1, bl , h1) Î³ where K1, b1 and h1 are orbitally excited axial vector mesons of K*, p and w respectively. At quark level, all these decays are governed by the flavor changing neutral currents bâ†’ (s, d) Î³ transitions, which are not allowed at tree level in the SM. These processes will provide quantitative information on the Standard Model parameters especially the CKM matrix elements and are also sensitive to the presence of physics beyond the SM. The exclusive decays are experimentally better accessible but pose more problem for the theoretical analysis. It is therefore imperative to firm up theoretical predictions in exclusive decays for precision tests of SM and to interpret data for possible new physics effects in these decays.
The main results of our work are the following:
Form factors parameterizing radiative leptonic decays of heavy mesons (B+â†’Î³l+vl) for photon energy are computed in the language of dispersion relations. The contributing states to the absorptive part in the dispersion relation are the multi particle continuum, estimated by quark triangle graph and resonances with quantum numbers 1- and 1+ which includes B* and B*A. and their radial excitations, which model the higher state contributions. Constraints provided by the asymptotic behavior of the structure dependent amplitude, Ward Identities and gauge invariance are used to provide useful information for parameters needed. The couplings gBB*Î³ and fBB*AÎ³ are predicted if we restrict to first radial excitation; otherwise using these as an input the radiative decay coupling constants for radial excitations are predicted. The value of the branching ratio for the process B+â†’Î³Âµ+vÂµ is found to be in the range 0.5 x 10-6. A detailed comparison is given with other approaches.
For Bâ†’ (K1, bl , h1) Î³ decays we calculate the hard spectator corrections in 0 (as) in the leading-twist approximation using Large Energy Effective Theory (LEET) techniques. Combining with the hard vertex, already calculated in the literature, and annihilation contributions, they are used to compute the branching ratios for these decays in the next-to-leading order (NLO) in the strong coupling as and in leading power in AQCD/MB. It is found that the theoretical branching ratios for the decays Bâ†’ K1 Î³ in the LEET approach can be compared with the data only for significantly large values of the form factors than their estimates in the Light Cone Sum Rules (LCSR). Using the SU (3) symmetry for the form factors, the branching ratio for Bâ†’ (bl , h1) Î³ is expressed in terms of the branching ratio of the Bâ†’ K1 Î³ and they are found to be B (Bâ†’b1Î³) = 0.53 x 10-6 and B (Bâ†’h1Î³) = 0.51 x 10-6.
We also calculate the direct GP asymmetry for the decays Bâ†’ (K1, bl , h1) Î³ and find, in conformity with the observations made in the literature, that the hard spectator contributions significantly reduce the asymmetry arising from the vertex corrections. The sensitivity of the GP asymmetry on the underlying parameters is found to be significantly large.