Eur. Phys. J. C (2007) 49: 665-674
https://doi.org/10.1140/epjc/s10052-006-0152-z

Regular Article - Theoretcial Physics

Form factors and branching ratio for the B→lνγ decay

National Center for Physics, Quaid-i-Azam University, Islamabad, 45320, Pakistan

^* e-mail: riazuddin@ncp.edu.pk

Received: 20 June 2006
Published online: 8 December 2006

Abstract

Form factors parameterizing radiative leptonic decays of heavy mesons (B⁺→γl⁺ν_l) against photon energy are computed in the language of dispersion relations. The states contributing to the absorptive part in the dispersion relation are the multiparticle continuum, estimated by the 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 the parameters needed. The couplings g_BB*γ and f_BBA*γ are predicted as we restrict ourselves to the first radial excitation; otherwise using these as an input the radiative decay coupling constants for the radial excitations are predicted. The value of the branching ratio for the process B⁺→γμ⁺ν_μ is found to be in the range 0.5×10^-6. A detailed comparison is given with other approaches.