Differential decay rate for B -> pi/NU semileptonic decays

We present our study on B --> pi/nu semileptonic decay form factors using N RQCD action for heavy quark. In the analysis, we use the form factors f(1) (v.k(pi)) and f(2) (v.k(pi)) defined in the context of heavy quark effectiv e theory by Burdman et al. Since the NRQCD action for heavy quark respects the heavy quark symmetry, our results are described by the HQET form factor s most naturally. From a quenched lattice QCD simulation at beta = 5.9 on a 16(3) x 48 lattice, we obtain the form factors f(1) (v.k(pi)) and f(2) (v. k(pi)), and find that their 1/m(B) correction is small. The limit of physic al heavy and light quark masses can be reached without introducing any mode l function, and we obtain a prediction for the differential decay rate d Ga mma /dq(2). We also discuss the soft pion limit of the form factors.