Centrality dependences of soft and hard components of pt distributions of negative pions in 4He+12C collisions at 4.2A GeV/c
Abstract
The dependences of the shapes of transverse momentum distributions of the negative pions, produced in minimum bias 4He+12C collisions at a momentum of 4.2 GeV/c per nucleon, on collision centrality and fitting range of pt were analyzed systematically. To study the change in slopes (temperatures) of the pt spectra of π- with changing collision centrality and fitting pt range, the pt spectra, extracted from the experimental data and quark–gluon string model (QGSM) calculations, were fitted by the one- and two-temperature Hagedorn and Boltzmann functions. Fitting of the experimental pt distributions of π- in both the whole pt and pt = 0.1–1.2 GeV/c intervals required the two-temperature functions for adequate description of spectra, in agreement with the previous findings for different sets of colliding nuclei and various energies. On the whole, the absolute values of the extracted temperatures were lower in case of fitting range pt = 0.1–0.7 GeV/c as compared to the fitting interval pt = 0.1–1.2 GeV/c. The one-temperature functions were sufficient for fitting satisfactorily the experimental pt distributions of the negative pions in range pt = 0.1–0.7 GeV/c. In contrast to the experimental temperatures, the extracted QGSM temperatures were not sensitive to collision centrality and fitting range of pt. The collision centrality dependences of the temperatures of soft (pt = 0.1–0.5 GeV/c) and hard (pt = 0.5–1.2 GeV/c) components of the experimental pt distributions of the negative pions in 4He+12C collisions at 4.2A GeV/c were studied separately. The extracted temperatures of both soft and hard components of pt distributions of π- depended on geometry (size) and degree of overlap of colliding nuclei in peripheral, semicentral and central 4He+12C collisions. The temperature of soft pt component of the negative pions was consistently larger in semicentral and central 4He+12C collisions than that in peripheral interactions. The temperature of hard pt component of π- in 4He+12C collisions decreased consistently with an increase in collision centrality. The physical interpretations of the observed centrality dependences of temperature (T) of soft and hard pt components of the negative pions in 4He+12C collisions were given.
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