Pseudorapidity Distribution of Charged Particles in $d+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$

The measured pseudorapidity distribution of primary charged particles in minimum-bias $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=\mathrm{200}\mathrm{G}\mathrm{e}\mathrm{V}$ is presented for the first time. This distribution falls off less rapidly in the gold direction as compared to the deuteron direction. The average value of the charged particle pseudorapidity density at midrapidity is $\langle d{N}_{\mathrm{c}\mathrm{h}}/d\eta {\rangle }_{\mid \eta \mid \le 0.6}=9.4\pm 0.7(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$ and the integrated primary charged particle multiplicity in the measured region is $82\pm 6(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$. Estimates of the total charged particle production, based on extrapolations outside the measured pseudorapidity region, are also presented. The pseudorapidity distribution, normalized to the number of participants in $d+\mathrm{A}\mathrm{u}$ collisions, is compared to those of $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ and $p+\overline{p}$ systems at the same energy. The $d+\mathrm{A}\mathrm{u}$ distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.

Figure 1

Minimum-bias pseudorapidity distributions of primary charged particles, $d{N}_{\mathrm{c}\mathrm{h}}/d\mathrm{\eta }$, measured for $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=\mathrm{200}\mathrm{G}\mathrm{e}\mathrm{V}$. (a) $d{N}_{\mathrm{c}\mathrm{h}}/d\mathrm{\eta }$ distributions obtained by explicit integration over centrality bins for each centrality measure. (b) Final $d{N}_{\mathrm{c}\mathrm{h}}/d\mathrm{\eta }$ distribution obtained by averaging over the five minimum-bias distributions. The gray band corresponds to the systematic errors (90% C.L.). The curve corresponds to a triple Gaussian fit to $d+\mathrm{A}\mathrm{u}$ collisions.

Figure 2

$d{N}_{\mathrm{c}\mathrm{h}}/d\eta$ distributions per participant are shown for minimum-bias $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=\mathrm{200}\mathrm{G}\mathrm{e}\mathrm{V}$ (solid circles), for central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions ($0–6\%$) [12] (triangles) and for $p+\overline{p}$ collisions from UA5 [19] (open squares) at the same energy. The systematic errors are shown by gray bands. The uncertainties on $\langle N_{\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}}\rangle$ for $d+\mathrm{A}\mathrm{u}$ and $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions have been added in quadrature to the gray bands.

Figure 3

Comparison of the measured minimum-bias pseudorapidity distribution for $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=\mathrm{200}\mathrm{G}\mathrm{e}\mathrm{V}$ to model predictions. (a) Comparison to the parton saturation [7] and RQMD [9] models. (b) Comparison to the predictions of the HIJING [8] model and the published AMPT model with and without final-state interactions (FSI) [10]. (c) Quantitative evaluation of the model predictions, expressed as the ratio of the model prediction to the data. The gray band corresponds to the systematic errors (90% C.L.) on the data.