  Recently, interesting data concerning $dN_{ch}/d\eta$ in Au-Au collisions
[$\eta=-\ln \tan (\theta/2)$] with centrality cuts have been reported from the
PHOBOS Collaboration. In most treatment these data are divided by the number of
participants (nucleons) in collisions. Instead of this method, we use the total
multiplicity $N_{ch} = \int (dN_{ch}/d\eta)d\eta$ and find that there is
scaling phenomenon among $(N_{ch})^{-1}dN_{ch}/d\eta = dn/d\eta$ with different
centrality cuts at $\sqrt{s_{NN}} = 130$ GeV. To explain this scaling behavior
of $dn/d\eta$, we employ a stochastic approach using the Ornstein-Uhlenbeck
process with two sources. A Langevin equation is adopted for this explanation.
Moreover, comparisons of $dn/d\eta$ at $\sqrt{s_{NN}} = 130$ GeV with that at
$\sqrt{s_{NN}} = 200$ GeV are made, and no significant difference is found. A
possible method fot the detection of the quark-gluon plasma (QGP) through
$dN_{ch}/d\eta$ is presented.
