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

Abstract

We present a quenched calculation of the form factors of the semileptonic weak decay $B \to πl \barν$ with $O(1/m_Q)$ NRQCD heavy quark and Wilson light quark on a $16^3 \times 32$ lattice at $β=5.8$. 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 $q^2_{max}$, even at the $b$-quark mass range. $f^0(q^2_{max})$ is compared with $f_B/f_π$ based on the soft pion theorem and significant difference is observed.