Semileptonic Decay of $B$-Meson into $D^{\ast \ast }$ and the Bjorken Sum Rule

Abstract

We study the semileptonic branching fraction of $B$-meson into higher resonance of charmed meson $D^{\ast \ast }$ by using the Bjorken sum rule and the heavy quark effective theory(HQET). This sum rule and the current experiment of $B$-meson semileptonic decay into $D$ and $D^{\ast }$ predict that the branching ratio into $D^{\ast \ast }l{\nu }_l$ is about 1.7\%. This predicted value is larger than the value obtained by the various theoretical hadron models based on the HQET.

Comments: 10 pages, LaTex, to be published in Phys. Lett. B