Pseudorapidity Distribution of Charged Particles in d + Au Collisions at $\sqrt{s_{_{NN}}$ = 200 GeV

Abstract

The measured pseudorapidity distribution of primary charged particles in minimum-bias d + Au collisions at ${\sqrt{s_{_{NN}}} = \rm {200 GeV}}$ 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 ${\rm < dN_{ch}/dη>_{\mid η\mid \le 0.6} = 9.4 \pm 0.7(syst)}$ and the integrated primary charged particle multiplicity in the measured region is 82 $\pm$ 6(syst). 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 + Au collisions, is compared to those of Au + Au and ${\rm p}+\bar{\rm p}$ systems at the same energy. The d + Au distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.