BC_NPI module for the analysis of Bc -> J/psi +n pi and Bc -> B_s +n pi decays within the EvtGen package

The module for the generation of $B_c$ meson decays into $J\mathrm{/}\psi +n\pi$ and $B_s^{(\ast )}+n\pi$ ($n\le 4$) is implemented into EvtGen program package. The decay amplitudes are calculated in the frame work of factorization model. Within this approach the decay can be represented as $B_c$ decay into $J/\psi (B_s)+W^$followedbythevirtual$W^$-bosondecayintothefinalsetof$\pi$-mesons. The described calculation technique allows to adopt the parameters of $W^{\ast }\to n\pi$ transition from the analysis of $\tau$ decay into ${\nu }_{\tau }+n\pi$. Comparison with available theoretical predictions is performed.