Pion chemical potentials as seen from transverse momentum distributions
We examine the transverse momentum spectra of negatively charged pions emitted in proton-proton, proton-antiproton, and nucleus-nucleus collisions at beam momenta from tens to hundreds of GeV$/c$. The measured spectra are described within the framework of nonextensive Tsallis statistics, allowing the corresponding chemical potentials to be determined through a quantitative comparison with experimental data. The extracted thermodynamic parameters are subsequently employed to explore the structure of the phase diagram in the chemical potential-temperature ($μ$-$T$) plane, with particular emphasis on identifying possible signatures of a phase transition. Within this interpretation, pion production in the midrapidity region is associated with a phase characterized by broken chiral symmetry, whereas increasing rapidity corresponds to an evolution toward a regime in which chiral symmetry is restored.