Search for the onset of baryon anomaly at RHIC-PHENIX

Tatsuya Chujo

One of the key questions at the relativistic heavy ion program at RHIC is that where is the onset of the high $p_T$ hadron yield suppression and baryon anomaly at RHIC, and how they evolve from SPS to RHIC energy. The beam energy survey data in Au+Au and Cu+Cu systems at RHIC may give us an answer to this important question by measuring the identified single particle spectra. In this talk, the experimental data on yields and particle ratios at SPS and RHIC will be reviewed, and the extracted hadron freeze-out properties will be studied as a function of beam energies and number of participant nucleons ($N_{part}$). We will also present the current analysis status on $\pi $/K/p (and their antiparticles) spectra in Cu+Cu at $\sqrt{s_{NN}}$ = 22.5 and 62.4 GeV measured by the PHENIX experiment. The evolution of the suppression pattern for both charged pions and (anti-)protons as a function of $\sqrt{s_{NN}}$ (and $N_{part}$) will be discussed.