$|V_{ub}|$ determination by $B to D_s pi$

We investigate $ovar{B^0} to D_s^- pi^+$ decay in perturbative QCD approach which has recently been applied to $B$ meson decays. $ovar{B^0} to D_s^- pi^+$ decay (and its charge conjugated mode) can be one of the hopeful modes to determine $|V_{ub}|$ since it occurs through $b to u$ transition only. We estimate both factorizable and non-factorizable contribution, and show that the non-factorizable contribution is much less than the factorizable one. Our calculation gives ${BR}(ovar{B^0} to D_s^- pi^+) = (50 sim 70) times f_{Ds}^2|{V_{ub}}{V_{cs}}|^2$.