Analysis of the exclusive semileptonic decay Lambda(b)->Lambda(c)+l(nu)over-bar(l) within a light-front constituent quark model

The exclusive semileptonic decay Lambda(b) --> Lambda(c) + l<(nu)over bar>( l) is investigated including both radiative and first-order power correctio ns in the inverse heavy-quark mass, while the Isgur-Wise function is calcul ated within a light-front constituent quark model. It turns out that the de pendence on the model parameters can be effectively constrained using recen t lattice QCD results at low values of the recoil. Our final predictions fo r the exclusive semileptonic branching ratio, the longitudinal and transver se asymmetries, and the longitudinal to transverse decay ratio are: Br(Lamb da(b) --> Lambda(c)l<(nu)over bar>e) = (6.3 +/- 1.6) % \V-bc/0.040\(2) tau( Lambda(b))/(1.24 ps), a(L) = -0.945 +/- 0.014, a(T) = -0.62 +/- 0.09 and R- L/T = 1.57 +/- 0.15, respectively. Moreover, the theoretical uncertainties both on a(L) and the (partially integrated) R-L/T are found to be quite sma ll and, therefore, the experimental determination of these quantities is a very interesting tool for testing the Standard Model and for investigating possible New Physics. In this respect the sensitivity to extract unique inf ormation both oil the strength and phase of possible hadronic right-handed currents is illustrated.