The study of hadron spectra at high $p_{ T}$ in p+p collisions provides a good test of perturbative quantum chromo-dynamic calculations (pQCD) and baseline for measurements of nuclear modification factors in Au+Au collisions. Using events triggered by the Barrel Electro-Magnetic Calorimeter, identified charged hadron transverse momentum ($p_T$) spectra are measured up to 15 GeV/$c$ at mid-rapidity ($\mid y\mid$ $<$ 0.5) and neutral kaon $p_T$ spectra up to 12 GeV/$c$ in p + p collisions at $\sqrt{ s_{ NN}}$ = 200 GeV. The particle ratios of $p/\pi^{ +}$, $\bar{ p}/\pi^{ -}$ and $K^{ \pm,0}$ / $\pi^{ \pm}$ in p + p collisions are shown and compared with next-to-leading order pQCD calculations. In central Au+Au collisions, we report nuclear modification factors ($R_{ AA}$) for pion, kaon, proton and $\rho$ and discuss several model calculations: color-charge dependence of jet quenching and jet conversion. Finally, centrality dependence of $R_{ AA}$ at high $p_T$ ($>$ 5.5 GeV/c) for kaon are compared with that of pion in Au + Au collisions at 200 GeV.
Categories: nucl-ex