Analysis of the Lambda(b)->Lambda(c)+l(nu)over-bar(l) decay within a light-front constituent quark model - art. no. 074018

We present an investigation of the Isgur-Wise form factor relevant for the semileptonic decay Lambda(b)-->Lambda(c) +l<(nu)over bar>(l) performed with in a light-front constituent quark model. Adopting different baryon wave fu nctions it is found that the Isgur-Wise form factor depends sensitively on the baryon structure. It is shown however that the shape of the Isgur-Wise function in the full recoil range relevant for the Lambda(b)-->Lambda(c) l<(nu)over bar>(l) decay can be effectively constrained using recent lattic e QCD results at low recoil. Then the Lambda(b)-->Lambda(c) + l<(nu)over ba r>(l) decay is investigated including both radiative effects and first-orde r power corrections in the inverse heavy-quark mass. Our final predictions for the exclusive semileptonic branching ratio, the longitudinal and transv erse asymmetries, and the longitudinal to transverse decay ratio are Br(Lam bda(b)-->Lambda(c)l<(nu)over bar>(l)) = (6.3 +/- 1.6)% \V-bc/0.040 (2)tau(L ambda(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, both the longitudinal asymmetry and the (partially integrated) longitudinal to transverse decay ratio are found to be only marginally affected by the model dependence of the Isgur-Wise form factor as well as by first-order power corrections; therefore, their exper imental determination might be a very interesting tool for testing the SM a nd for investigating possible new physics. [S0556-2821(99)06817-4].