Narrow Results

The collision centrality dependencies of the average kinematical characteristics of the negative and positive pions, produced in ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions at $4.2A\mathrm{\text{GeV}}/c$, were investigated. The ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ proved to be $1.20\pm 0.05$, $1.08\pm 0.04$ and $1.04\pm 0.03$ in the peripheral, semicentral, and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collision events, respectively, decreasing noticeably with increasing collision centrality. The suppression (decrease) of the ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ was observed in the semicentral and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions as compared to the ratio $(\approx 1.22)$, estimated using the simple model for ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collision system. The ratio $〈n({\pi }^{-})〉/〈n({\pi }^{+})〉$ estimated using the simple model agreed well with the corresponding ratio $(\approx 1.24)$, estimated for ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions at $4.2A\mathrm{\text{GeV}}/c$ based on the Wounded Nucleon Model (WNM). Comparison of the emission angle as well as momentum distributions of the charged pions in the peripheral and central ${}^{12}\mathrm{\text{C}}+{}^{181}\mathrm{\text{Ta}}$ collisions revealed the significant decrease of the fraction of the relatively fast charged pions (with smaller emission angles) and increase of the fraction of the relatively slow charged pions (with larger emission angles) with an increase in collision centrality. The results of the present analysis can be useful for analysis of the centrality dependence of the charged pion production in heavy ion collisions at high energies.