Produce
signal channel :
B\to D^*(\to K \pi) e(\mu) \nu
B\to D^*(\to K \pi) \tau(\to e(\mu)) \nu and
B\to D^*(\to K \pi) \tau(\to e(\mu)) \nu
background channel :
B\to D^{**} e \nu
B\to D^{**} \tau(\to e) \nu
With UT, and without \Delta M_{D^*} cut
\Delta M_{D^*}