First study of $B\to \pi$ semileptonic decay form factors using NRQCD

Abstract

We present a quenched calculation of the form factors of the semileptonic weak decay $B\to \pi l\bar{\nu }$ with $O(1/m_Q)$ NRQCD heavy quark and Wilson light quark on a $16^3\times 32$ lattice at $\beta =5.8$. The form factors are evaluated at six heavy quark masses, in the range of $m_Q\sim 1.5-8$ GeV. $1/m_Q$ dependence of matrix elements are investigated and compared with HQET predictions. We observe clear signal for the form factors near $q_{max}^2$, even at the $b$-quark mass range. $f^0(q_{max}^2)$ is compared with $f_B/f_{\pi }$ based on the soft pion theorem and significant difference is observed.

Comments: 3 pages, 5 ps figures, uses espcrc2.sty and epsf.sty, Talk presented at Lattice'97