High $p_T$ Measurements from PHENIX

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 $\pi^0$ 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.