Exclusive semi-leptonic decays of bottom mesons in the spectator quark model

Abstract

We calculate the exclusive semileptonic bottom meson decays$B \to D(D*) + l^ - + \bar v_l$ in the spectator quark model. The helicity structure of the mesonic current transitionsB→D(D ^*) is matched to the helicity structure of the free quark current transitionsb→c at minimum momentum transferq ²=0. The results are continued toq ²≠=0 by pole-dominated form factors. Our results are compared to recent calculations that use quark model dynamics at maximum momentum transferq ²_max = (M ₁ −M ₂)². We find agreement atq ²_max . Atq ²=0 there are significant differences between the predictions of the two approaches leading to marked differences in the predictions for the shape of the lepton energy spectrum, the shape of theq ²-distribution, and the helicity composition of the transition measurable in the angular distributions of the decaysD ^*→Dπ and$W_{virtual}^ - \to l^ - + \bar v_l$.