One of the most exciting discoveries from the first RHIC operations is the suppression effect of high particles. PHENIX has observed clear effect not only for charged particles, but also for as identified pions as shown in Fig.3 [PHENIX, PRL 88, 022301(2002)].
This effect has been discussed in terms of "Jet Quenching Effect", which is considered as an important probe for early stage of collisions where QGP might exist. PHENIX results show that there seems to be a difference between and charged particles; suppression of seems to be larger. Considering the fact that protons exceeds pions above GeV/c, observed difference may be due to the larger contributions of protons, which is considered also as an evidence of the large gluon density [I. Vitev, M. Gyulassy, Hep-ph/0108045]. Measurements of proton and kaon at higher pt region together with existing data would shed light on this effect. Thus, particle identification of /K/p at higher region is strongly required.