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Register a new userPure Leptonic Radiative Decays $B^pm, D_stoell ugamma$ and the Annihilation Graph
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Pure leptonic radiative decays of heavy-light mesons are calculated using a very simple non-relativistic model. Dominant contribution originates from photon emission from light initial quark. We find $BR(B^pmtoell ugamma)sim3.5times10^{-6}$ and $BR(D_sto ell ugamma)sim1.7 times10^{-4}$. The importance of these reactions to clarify the dynamics of the annihilation graph is emphasized.
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Radiative and leptonic decays of B-mesons represent an excellent laboratory for the search for New Physics. I present here recent results on radiative and leptonic decays from the Belle and BABAR collaborations.
We investigate the pure annihilation type radiative $B$ meson decays $B^0 to phi gamma$ and $B_s to rho^0(omega)gamma$ in the soft-collinear effective theory. We consider three types of contributions to the decay amplitudes, including the direct annihilation topology, the contribution from the electro-magnetic penguin operator and the contribution of the neutral vector meson mixings. The numerical analysis shows that the decay amplitudes are dominated by the $omega-phi$ mixing effect in the $B^0 to phigamma$ and $B_s to omegagamma$ modes. The corresponding decay branching ratios are enhanced about three orders of magnitudes relative to the pure annihilation type contribution in these two decay channels. The decay rate of $B_s to rho^0gamma$ is much smaller than that of $B_s to omegagamma$ because of the smaller $rho^0-phi$ mixing. The predicted branching ratios $B(B^{0}rightarrowphigamma)=(3.99^{+1.67}_{-1.46} )times10^{-9},,B(B_srightarrowomegagamma)=(2.01^{+0.81}_{-0.71} )times10^{-7}$ are to be tested by the Belle-II and LHC-b experiments.
In this paper, we summarize the existing methods of solving the evolution equation of the leading-twist $B$-meson LCDA. Then, in the Mellin space, we derive a factorization formula with next-to-leading-logarithmic (NLL) resummation for the form factors $F_{A,V}$ in the $B to gamma ell u$ decay at leading power in $Lambda/m_b$. Furthermore, we investigate the power suppressed local contributions, factorizable non-local contributions (which are suppressed by $1/E_gamma$ and $1/m_b$), and soft contributions to the form factors. In the numerical analysis, which employs the two-loop-level hard function and the jet function, we find that both the resummation effect and the power corrections can sizably decrease the form factors. Finally, the integrated branching ratios are also calculated for comparison with future experimental data.
In this work, we study the radiative leptonic decays of $B^-$ and $D^-$ mesons using factorization approach. Factorization is proved to be valid explicitly at 1-loop level at any order of $O(Lambda_{rm QCD}left/m_Qright.)$. We consider the contribution in the soft photon region that $E_{gamma} sim left. Lambda^2_{rm QCD} /right. m_Q$. The numerical results shows that, the soft photon region is very important for both the $B$ and $D$ mesons. The branching ratios of $Bto gamma e u_e$ is $5.21times 10^{-6}$, which is about $3$ times of the result obtained by only considering the hard photon region $E_{gamma}sim m_Q$. And for the case of $Dto gamma e u_e$, the result of the branching ratio is $1.92times 10^{-5}$.
Adding a hard photon to the final state of a leptonic pseudoscalar-meson decay lifts the helicity suppression and can provide sensitivity to a larger set of operators in the weak effective Hamiltonian. Furthermore, radiative leptonic $B$ decays at high photon energy are well suited to constrain the first inverse moment of the $B$-meson light-cone distribution amplitude, an important parameter in the theory of nonleptonic $B$ decays. We demonstrate that the calculation of radiative leptonic decays is possible using Euclidean lattice QCD, and present preliminary numerical results for $D_s^+ to ell^+ ugamma$ and $K^- to ell^-bar{ u}gamma$.
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