Identified charged-hadron production in p + Al, 3 He +Au, and Cu + Au collisions at √sNN = 200 GeV and in U + U collisions at √sNN = 193 GeV

The PHENIX experiment has performed a systematic study of identified charged-hadron (π±, K±, p, ¯p) production at midrapidity in p + Al, 3 He +Au, and Cu + Au collisions at √sNN = 200 GeV and U + U collisions at √sNN = 193 GeV. Identified charged-hadron invariant transverse-momentum (pT ) and transverse-mass (mT ) spectra are presented and interpreted in terms of radially expanding thermalized systems. The particle ratios of K/π and p/π have been measured in different centrality ranges of large (Cu + Au and U + U) and small (p + Al and 3 He +Au) collision systems. The values of K/π ratios measured in all considered collision systems were found to be consistent with those measured in p + p collisions. However, the values of p/π ratios measured in large collision systems reach the values of ≈0.6, which is a factor of ≈2 larger than in p + p collisions. These results can be qualitatively understood in terms of the baryon enhancement expected from hadronization by recombination. Identified charged-hadron nuclear-modification factors (RAB) are also presented. Enhancement of proton RAB values over meson RAB values was observed in central 3 He +Au, Cu + Au, and U + U collisions. The proton RAB values measured in the p + Al collision system were found to be consistent with RAB values of φ, π±, K±, and π0 mesons, which may indicate that the size of the system produced in p + Al collisions is too small for recombination to cause a noticeable increase in proton production.