Energy Dependence of Particle Multiplicities in Central $Au+Au$ Collisions

We present the first measurement of the pseudorapidity density of primary charged particles in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{}\mathrm{GeV}$. For the $6\%$ most central collisions, we obtain ${\mathrm{dN}}_{\mathrm{ch}}/d\eta {|}_{|\eta |<1\mathrm{}}=650\mathrm{}\pm 35\left(\mathrm{syst}\right)$. Compared to collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$, the highest energy studied previously, an increase by a factor of $1.14\pm 0.05$ at $90\%$ confidence level, is found. The energy dependence of the pseudorapidity density is discussed in comparison with data from proton-induced collisions and theoretical predictions.