Analysis of rapidity spectra of negative pions ind + 12C,12C + 12C, and12C + 181Ta collisions at 4.2 GeV/cper nucleon

The experimental rapidity distributions of negative pions were studied in minimum bias $d+{}^{12}$C, ${}^{12}$C + ${}^{12}$C, and ${}^{12}$C + ${}^{181}$Ta collisions at 4.2 GeV/$c$ per nucleon with 4\ensuremath{\pi} acceptance. The quantitative analysis of centrality dependence of the rapidity as well as transverse momentum versus rapidity spectra of the negative pions in the above collisions was performed by fitting the pion spectra with a Gaussian function. The widths of the rapidity spectra of ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons decreased in going from peripheral to central $d+{}^{12}$C, ${}^{12}$C + ${}^{12}$C, and ${}^{12}$C + ${}^{181}$Ta collisions. With an increase in collision centrality, the centers of the rapidity distributions of the negative pions shifted towards the target fragmentation region in the case of asymmetric $d+{}^{12}$C and ${}^{12}$C + ${}^{181}$Ta collisions and remained at the midrapidity position for symmetric ${}^{12}$C + ${}^{12}$C collisions. The extracted widths and locations of the centers of transverse momentum versus rapidity spectra of the negative pions did not depend within uncertainties on the masses of the projectile and target nuclei as well as the collision centrality. The experimental results were compared systematically with the corresponding results extracted by using a version of the quark-gluon-string model adapted to intermediate energies.