Centrality and system-size dependencies of temperatures of soft and hard components ofptdistributions of negative pions inHe4+C12,C12+C12, andC12+Ta181collisions atsNN=3.14GeV

Abstract

Collision centrality as well as the system-size dependencies of the temperatures of the soft (${p}_{t}=0.1\ensuremath{-}0.5\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$) and hard (${p}_{t}=0.5\ensuremath{-}1.2\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$) components of the experimental transverse momentum distributions of the negative pions produced in $^{4}\mathrm{He}{+}^{12}\mathrm{C}, ^{12}\mathrm{C}{+}^{12}\mathrm{C}$, and $^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ collisions at $4.2A\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$ ($\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$) are analyzed. For the studied collision systems and selected collision centralities, the temperatures are extracted from fitting separately the soft and hard ${p}_{t}$ components of the negative pions by one-temperature Hagedorn and one-temperature Boltzmann functions. The extracted temperatures of both the soft and hard components of the ${p}_{t}$ distributions of ${\ensuremath{\pi}}^{\ensuremath{-}}$ depend on the geometry (size) and degree of overlap of the colliding nuclei in peripheral, semicentral, and central nucleus--nucleus collisions at $\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. The gap (differences) between the extracted temperatures in the studied collision systems increases with increasing the degree of overlap of the colliding nuclei, i.e., with an increase in the collision centrality and the corresponding increase in the numbers of participant nucleons and binary collisions. The temperature of the soft ${p}_{t}$ component of the negative pions in $^{12}\mathrm{C}{+}^{12}\mathrm{C}$ ($^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$) collisions increases (decreases) with increasing of the collision centrality. The temperature of the hard ${p}_{t}$ component of ${\ensuremath{\pi}}^{\ensuremath{-}}$ in $^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ ($^{4}\mathrm{He}{+}^{12}\mathrm{C}$) collisions increases (decreases) consistently with an increase in the collision centrality. The temperature of the soft ${p}_{t}$ component of ${\ensuremath{\pi}}^{\ensuremath{-}}$ decreases with an increase in the system size in semicentral and central nucleus--nucleus collisions at $\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. In central collisions, the temperature of the hard ${p}_{t}$ component increases consistently with an increase in system size. The physical interpretations of the results obtained are given. The quantitative results on temperatures extracted from the ${p}_{t}$ spectra of negative pions in nucleus--nucleus collisions at $4.2A\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$ are compared to those obtained in lower, intermediate, and higher energies in other Joint Institute for Nuclear Research (JINR), Gesellschaft f\"ur Schwerionenforschung (GSI), and SPS experiments.