Charged particle rapidity distributions at RHIC

Using a multiphase transport model (AMPT), which includes both initial partonic and final hadronic scattering, we study the rapidity distributions of charged particles such as protons, antiprotons, pions and kaons in central Au+Au collisions at $\sqrt s$ = 56, 130, and 200 AGeV at RHIC. We find that present data at 56 and 130 AGeV by the PHOBOS collaboration are consistent with a rather weak jet quenching in the initial dense matter. We also find that the antiproton to proton ratio at mid-rapidity increases appreciably with $\sqrt s$, indicating the approach to a nearly baryon-antibaryon symmetric matter in high energy collisions. Furthermore, the $K^+/\pi^+$ ratio is almost constant within the energy range studied here, suggesting the approximate chemical equilibrium for strangeness production in these collisions.