On centrality and rapidity dependences of transverse momentum spectra of negative pions in ¹²C + ¹²C collisions at 4.2 GeV/c per nucleon

The dependences of the experimental transverse momentum spectra of the negative pions, produced in minimum bias ¹²C + ¹²C collisions at a momentum of 4.2A GeV/c, on the collision centrality and the pion rapidity range were studied. To analyze quantitatively the change in the p_t spectra of π^- mesons with the changes of collision centrality and pion rapidity range, the extracted p_t spectra were fitted by Hagedorn, Boltzmann, simple exponential and Gaussian functions. The values of the extracted spectral temperatures T₁ and T₂ were consistently larger for the p_t spectra of π^- mesons coming from midrapidity range as compared to those of the negative pions generated in the target and projectile fragmentation regions. The spectral temperatures T₁ and T₂ extracted from fitting the p_t spectra of π^- mesons in range p_t = 0.1–1.2 GeV/c practically coincided with each other in peripheral, semicentral and central ¹²C + ¹²C collision events, and thus did not show any collision centrality dependence. However, the values of T₁ and T₂ extracted from fitting in range p_t = 0.1–0.7 GeV/c were consistently and noticeably larger in case of central collisions as compared to peripheral and semicentral ¹²C + ¹²C collisions. Hagedorn and Boltzmann functions provided significantly better fits of the transverse momentum spectra of the negative pions with the physically acceptable values of the extracted temperatures as compared to Gaussian and simple exponential functions. (author)