Factorization of Radiative Leptonic Decays of BB^- and DD^- Mesons Including the Soft Photon Region


In this work, we study the radiative leptonic decays of BB^- and DD^- mesons using factorization approach. Factorization is proved to be valid explicitly at 1-loop level at any order of O(ΛQCD/mQ)O(\Lambda_{\rm QCD}\left/m_Q\right.). We consider the contribution in the soft photon region that EγΛQCD2/mQE_{\gamma} \sim \left. \Lambda^2_{\rm QCD} /\right. m_Q. The numerical results shows that, the soft photon region is very important for both the BB and DD mesons. The branching ratios of BγeνeB\to \gamma e\nu_e is 5.21×1065.21\times 10^{-6}, which is about 33 times of the result obtained by only considering the hard photon region EγmQE_{\gamma}\sim m_Q. And for the case of DγeνeD\to \gamma e\nu_e, the result of the branching ratio is 1.92×1051.92\times 10^{-5}.Comment: arXiv admin note: text overlap with arXiv:1409.035

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