  It has been known that $B \rightarrow D^{(*)} \tau \nu_{\tau}$ are good
observables in the search for the charged Higgs. The recent obervation of
deviation from standard-model by almost 4$\sigma$ by Babar, Belle and LHCb in
$R(D^{(*)})$ revived the interest in possible signal of presence of charged
Higgs in these modes. But such a large deviation in the rates, where
standard-model has tree level contribution, coming from a charged Higgs alone
is highly unlikely. However these decay modes are good probes to search for
small charged Higgs signal if we can construct sensitive observables in these
modes. In this work we would like to propose four new observables which shows
much more sensitivity to the presence of charged Higgs than the usual
observables such as $A_{\lambda}^{D^{(*)}}$ and $A_{\theta}^{D^{(*)}}$. These
four observable are (1) $\frac{1}{A_{\lambda}^{D}}$,\ (2) $Y_{1}(q^{2}) =
\frac{A^{D}_{\theta}}{A^{D}_{\lambda}}$,\ (3) $Y_{2}(q^{2}) = \frac{d\Gamma(B
\rightarrow D^{*}\tau\nu_{\tau})}{d\Gamma_{D}(\lambda_{\tau}=+1/2) -
d\Gamma_{D}(\lambda_{\tau}=-1/2)}$ and (4) $Y_{3}(q^{2}) =
(\frac{q^{2}}{m^{2}_{\tau}})(A^{D}_{\lambda} + 1)\frac{1}{A^{D}_{\lambda}}$.
