Two-Particle Jet-Correlations from STAR: Systematics from Charged Hadrons and First Result for Net-Charges

Two-particle jet-like correlations of charged hadrons with a high $p_T$ trigger particle are strongly modified at RHIC, lending strong support for jet quenching and partonic energy loss. We present a systematic study of 2-particle jet-correlations in azimuth ($\Delta\phi$) and pseudo-rapidity ($\Delta\eta$) as a function of trigger and associated particle $p_T$, system size, and collision centrality. In central heavy-ion collisions, significant excess of correlated particles are found on the away-side at about 1 radian away from $\Delta\phi=\pi$, and those correlated particles are observed to possess a larger average $\langle p_T \rangle$ than those at $\pi$. In order to investigate the physics mechanisms underlying these observations, azimuthal correlations of net-charges, reflecting mostly net-protons, are analyzed. First result from the analysis will be reported.