Charged particle multiplicity near mid-rapidity in central Au+Au collisions at $\sqrt{s}=$ 56 and 130 AGeV

Abstract

We present the first measurement of pseudorapidity densities of primary charged particles near mid-rapidity in Au+Au collisions at $\sqrt{s}=$ 56 and 130 AGeV. For the most central collisions, we find the charged particle pseudorapidity density to be $dN/d\hat{I}\cdot {|}_{|\hat{I}\cdot |<1}=408\pm 12(stat)\pm 30(syst)$ at 56 AGeV and $555\pm 12(stat)\pm 35(syst)$ at 130 AGeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.

4 pages, 4 figures, revtex (submitted to Phys. Rev. Letters), revised Fig. 4