Analysis of the Lambda_b -> Lambda_c + l nu_l decay within a light-front constituent quark model

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  • 20 October 1998
Abstract
We present an investigation of the Isgur-Wise form factor relevant for the semileptonic decay Lambda_b -> Lambda_c + l nu_l performed within a light-front constituent quark model. Adopting different baryon wave functions it is shown that the Isgur-Wise form factor depends sensitively on the baryon structure. The shape of the Isgur-Wise function is effectively constrained using recent lattice QCD results as well as model-independent dispersive bounds on its slope and curvature at the zero-recoil point. Then, the Lambda_b -> Lambda_c + l n_l decay is investigated including also first-order power corrections in the inverse heavy quark mass. Our final predictions for the exclusive semileptonic branching ratio, the longitudinal and transverse asymmetries, and the longitudinal to transverse decay ratio are: Br(SL) = (7.3 +- 1.6) % |V_bc / 0.040|**2 tau(Lambda_b) / (1.24 ps), a(L) = -0.94 +- 0.01, a(T) = -0.6 +- 0.1 and R(L/T) = 1.6 +- 0.1, respectively. In particular, both the longitudinal asymmetry a(L) and the longitudinal to transverse decay ratio R(L/T) are found to be only marginally affected by the model dependence of the Isgur-Wise form factor as well as by power corrections. Therefore, their experimental determination could be a very interesting tool for testing the SM and for investigating possible New Physics.

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