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

We calculate the exclusive semileptonic bottom meson decaysB to D(D*) + l^ - + bar v_l in the spectator quark model. The helicity structure of the mesonic current transitions B→ D( D ^*) is matched to the helicity structure of the free quark current transitions b→ c at minimum momentum transfer q ²=0. The results are continued to q ²≠=0 by pole-dominated form factors. Our results are compared to recent calculations that use quark model dynamics at maximum momentum transfer q {_max/²} = ( M ₁ - M ₂)². We find agreement at q {_max/²}. At q 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 the q ²-distribution, and the helicity composition of the transition measurable in the angular distributions of the decays D ^*→ Dπ andW_{virtual}^ - to l^ - + bar v_l.