High $p_T$ Measurements from PHENIX

TL;DR

PHENIX analyzes high-pT particle production in Au+Au and p+p collisions at √sNN=200 GeV to quantify medium-induced modifications. Using spectra, the nuclear modification factor R_AA, and jet-like correlations, the study finds strong suppression of π0 and charged hadrons in central collisions, consistent with parton energy loss in a dense medium and evolving with centrality. The results reveal a notable baryon/meson composition at high pT and provide jet evidence via two-particle correlations, reinforcing the jet fragmentation interpretation in heavy-ion environments. Overall, the work establishes significant jet quenching and centrality-dependent suppression, with implications for partonic energy loss mechanisms in the quark-gluon plasma.

Abstract

We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5-6 for neutral pions and 3-4 for charged hadrons in central collisions at high $p_T$. We find that the ratio of $π^0$ to $(h^++h^-)/2$ remains nearly constant at $\sim 0.5$ for $p_T = 2-9$ GeV/c. Finally we present strong evidence for the observation of jets in Au+Au collisions.

Figures (11)

• Figure 1: Neutral pion production cross section vs. $p_T$ in p+p collisions at $\sqrt{s_{NN}} = 200$ GeV.
• Figure 2: Invariant yields of $(h^++h^-)/2$ as a function of $p_T$ in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV jjia and 130 GeV for centrality selections of 0-10% and 60-92%.
• Figure 3: Invariant yields of $\pi^0$ as a function of $p_T$ in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and 130 GeV for centrality 0-10% and $\sqrt{s_{NN}} = 200$ GeV for centrality 70-80%.
• Figure 4: $R_{AA}$ ($\pi^0$) for central Pb+Pb collisions at $\sqrt{s_{NN}}=17$ GeV and central Au+Au collisions at $\sqrt{s_{NN}}=130$ GeV. The error bars are the statistical $\oplus$$p_T$-dependent systematic errors. The brackets/boxes are the errors on the normalization of this ratio.
• Figure 5: $R_{AA}$ ($\pi^0$) for central and peripheral Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. The error bars are the statistical $\oplus$$p_T$-dependent systematic errors. The shaded boxes are the errors on the normalization of the ratio.