Mean pion multiplicities in Ar+Sc collisions

Preliminary results for mean negatively charged pion multiplicities $\langle \pi^- \rangle$ using the $h^-$ method are presented for central Ar+Sc collisions at 13, 19, 30, 40, 75 and 150\textit{A} GeV/c beam momentum. The data were recorded by the NA61/SHINE detector at the CERN SPS. Starting with rapidity distributions ${dn}/{dy}$ the procedure of obtaining total multiplicities is presented. The mean number of wounded nucleons $\langle W\rangle$ extracted from the Glissando MC model is used to calculate the ratio $\langle \pi^- \rangle/\langle W\rangle.$ The results are compared to those from other experiments and their dependence on colliding systems and collision energy is discussed.