Bound on V+A admixture in the b -> c current from inclusive vs. exclusive semileptonic decays of B mesons

An admixture of a right-handed $b\to c$ current in the semileptonic weak decays of the $B$ mesons would give a significantly different contribution to the inclusive rate of the decays $B\to l\nu X_c$ as compared to the exclusive decay $B\to D^{\ast }l\nu$ at zero recoil. Thus a difference in the values of $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ extracted from the data on these two types of decay would measure such admixture. The present marginal mismatch in determination of $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ by the two methods can be interpreted as corresponding to $g_R/g_L \approx 0.14 \pm 0.18$.