New Approach for Measuring $|V_{ub}|$ at Future $B$-Factories

It is suggested that the measurements of hadronic invariant mass ($m_X$) distributons in the inclusive $B \rightarrow X_{c(u)} l \nu$ decays can be useful in extracting the CKM matrix element $|V_{ub}|$. We investigated hadronic invariant mass distributions within the various theoretical models of HQET, FAC and chiral lagrangian as well as ACCMM model. It is also emphasized that the $m_X$ distribution even at the region $m_{X} > m_{D}$ in the inclusive $b\rightarrow u$ are effetive in selecting the events, experimentally viable at the future asymmetric $B$ factories, with better theoretical understandings.