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 $dN/dη|_{|η|<1} = 408 \pm 12 {(stat)} \pm 30 {(syst)}$ 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.

Figures (4)

• Figure 1: Detector setup for the initial running period. The insert shows the $\eta$ acceptance of the SPEC and VTX subdetectors as a function of primary vertex position.
• Figure 2: Paddle signal distribution for data events at $\sqrt{s} =$ 130 AGeV.
• Figure 3: Tracklet pseudorapidity density in the detector acceptance per event for data at $\sqrt{s} =$ 56 (circles) and 130 AGeV (triangles) for SPEC (left) and VTX (right), in comparison to scaled HIJING simulations (solid lines).
• Figure 4: Measured pseudorapidity density normalized per participant pair for central Au+Au collisions. Systematic errors are shown as shaded area. Data are compared with $p\overline{p}$ data and Pb+Pb data from the CERN SPS. Also shown are results of a HIJING simulation (with a line to guide the eye) and a parametrization of the $p\overline{p}$ data [7].