Relativistic Flux Tube Model Calculation of the Isgur-Wise Function

Abstract

The Relativistic Flux Tube model is used to calculate of the Isgur-Wise functions describing the exclusive semileptonic decays of $\bar{B}$ and ${\bar{B}}_s$ mesons. The light quark mass dependence is investigated and the predicted universal function agrees well with the results of lattice simulations, and with the experimental data. Recent experimental measurements of the $\bar{B}\text{ra}{D}^{\ast }l{\bar{\nu }}_l$ decay distribution yield the CKM element $V_{bc}=0.035\pm 0.001$. The IW function slope and second derivative at the zero recoil point are predicted to be ${\xi }^{\prime }(1)=-0.93\pm 0.04$ and ${\xi }^{\prime \prime }(1)=1.7\pm 0.1$ for a range of light quark massses. The importance of including higher derivatives in analyses of experiment is emphasized.

Comments: Latex (uses epsf macro), 14 pages of text, 6 postscript figures included. MAD/PH/851