A complete determination of New Physics parameters in leptonic decays of $\mathbf{B_{s}^0}$
Recently LHCb has measured the branching ratio of the rare decay of $B_s^0\rightarrow \mu^+ \mu^- $ as $2.9^{+1.1}_{-1.0} \times10^{-9}$ which is at par with the predicted standard model (SM) value. This result does not predict the absence of new physics (NP), rather it confines the NP parameter-space in a more stringent fashion. In this paper we have used the general loop level Hamiltonian to constrain the parameter space for the NP couplings for $B_s^0\rightarrow \mu^+ \mu^- $ from the experimental branching ratio. Using the available parameter space for these couplings, we have explored the angular analysis of the cascade decay of $B^0_{s}\to \tau^+\tau^- \to (\rho^+\bar{\nu}_\tau)_{\tau^+}(\pi^{-}\nu_{\tau})_{\tau^-} \to ((\pi^+ \pi^0)_{\rho^+}\bar{\nu}_\tau)_{\tau^+}(\pi^{-}\nu_{\tau})_{\tau^-}$. This analysis shows presence of NP can be identified by the angular analysis and also shows how to isolate the NP contribution from the SM. We believe that in future with the reduced error in the branching ratio measurement and better $\tau$ cone reconstruction technique we will be able to probe NP signal using this angular analysis.