Leptonic Decays Of Heavy Mesons Research Articles

Form factors and branching ratio for the B→lνγ decay

Form factors parameterizing radiative leptonic decays of heavy mesons (B+→γl+νl) 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 BA * 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 gBB*γ and fBBA*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+νμ is found to be in the range 0.5×10-6. A detailed comparison is given with other approaches.

Radiative leptonic decays of heavy mesons in heavy quark limit

We study the radiative leptonic decays of heavy mesons within the covariant light-front model. Using this model, both the form factors F_V and F_A have the same form when the heavy quark limit is taken. In addition, the relation between the form factor F_V and the decay constant of heavy meson F_H is obtained. The hadronic parameter \beta can be determine by the parameters appearing in the wave function of heavy meson. We find that the value of \beta is not only quite smaller than the one in the non-relativistic case, but also insensitive to the value of light quark mass m_q. These results mean that the relativistic effects are very important in this work. We also obtain the branching ratio of B\to l\nu_l \gamma is about (1.40-1.67)\times 10^{-6}, in agreement with the general estimates in the literature.

ISOBAR RESCATTERING MODEL AND LIGHT SCALAR MESONS

We use a toy model to discuss the problem of parameterizing the possible contribution of a light scalar meson, sigma, to the final state interactions in the non leptonic decays of heavy mesons.

Radiative leptonic decays ofBmesons in QCD

We compute the form factors parametrizing radiative leptonic decays of heavy mesons ${B}^{+}\ensuremath{\rightarrow}\ensuremath{\gamma}{e}^{+}\ensuremath{\nu}$ for photon energies much larger than ${\ensuremath{\Lambda}}_{\mathrm{QCD}},$ where perturbative QCD methods for exclusive processes can be combined with the heavy quark effective theory. The form factors can be reliably obtained in this region in an expansion in powers of $\ensuremath{\Lambda}{/E}_{\ensuremath{\gamma}}.$ The leading term in this expansion displays an additional spin symmetry manifested in the equality of form factors of vector and axial vector currents. The leading twist form factors can be written as the convolution of the B meson light-cone wave function with a hard scattering amplitude, which is explicitly calculated to one-loop order. The Sudakov double logarithms of the form $[({\ensuremath{\alpha}}_{s}/\ensuremath{\pi}){\mathrm{log}}^{2}{(2E}_{\ensuremath{\gamma}}/\ensuremath{\Lambda}){]}^{n}$ are resummed to all orders. As an application we present a method for determining the CKM matrix element $|{V}_{\mathrm{ub}}|$ from a comparison of photon spectra in B and D radiative leptonic decays.

Semileptonic decays of heavy mesons

The semileptonic and leptonic decays of heavy mesons are studied as a phenomenological application and exploration of a heavy-quark limit of Dyson-Schwinger equations. The single form factor, $\xi(w)$, which characterises the semileptonic decay in this limit, is calculated and compares well with recent experimental extractions. We obtain a lower bound of 1/3 on the slope-parameter $\rho^2 \equiv -\xi^\prime(1)$, which, in calculations with realistic input, is exceeded by a great deal: agreement with experimental data requiring $\rho^2 \sim 1.2 - 1.6$. The flavour and momentum dependence of the light-quark propagators has observable consequences.

Radiative leptonic decays of heavy mesons.

We compute the photon spectrum and the rate for the decays $B(D)\to l\nu_l\gamma$ These photonic modes constitute a potentially large background for the purely leptonic decays which are used to extract the heavy meson decay constants. While the rate for $D\to l\n\g$ is small, the radiative decay in the $B$ meson case could be of comparable magnitude or even larger than $B\to\m\n$. This would affect the determination of $f_B$ if the $\tau$ channel cannot be identified. We obtain theoretical estimates for the photonic rates and disscuss their possible experimental implications.