Draft Abstract for Fall DNP Meeting (Michigan State University)

From: Stephen J. Sanders (ssanders@ku.edu)
Date: Thu Jun 27 2002 - 16:56:52 EDT

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    Hi,
Below is a draft abstract that I would like to submit to the mini-symposium
on "Gluon Saturation at RHIC" at the Fall DNP meeting.  The
abstract deadline is Monday so please send comments and corrections before
then.  Thanks. 

...steve



ABSTRACT:
Charged-Particle Pseudorapidity Densities at BRAHMS

S.J. Sanders for the BRAHMS Collaboration

One of the suggested signatures for a saturation of the number of parton
collisions in central nucleus-nucleus collisions at higher energies is a
limit on the production of charged particles [1-3].  The BRAHMS experiment
has measured charged-particle pseudorapidity densities as a function
collision centrality at sqrt[s_nn]=130 GeV [4] and 200 GeV [5] for the
pseudorapidity range of ­4.7<=eta<=4.7.  Close to beam rapidity, the
pseudorapidity densities at the two energies scale in a manner consistent
with a limiting fragmentation picture in which the excitations of the
fragment baryons saturate at a moderate collision energy, independent of
system size.  At mid-rapidity for the 5% most central events we find a 14%
increase in pseudorapidity density at sqrt[s_nn]=200 GeV relative to
sqrt[s_nn]=130 GeV. The calculations of Kharzeev and Levin [3], which
include gluon saturation effects,  are in reasonable agreement with this
result.  We note, however, that an alternative calculation [6] gives
comparably good results without including saturation effects.  This talk
will present the BRAHMS results at the two RHIC energies in the context of
current models. Data on p+p scattering at the highest RHIC energy will also
be presented.



[1] L.V. Gribov, E.M Levin and M.G. Ryskin, Phys. Rep. 100, 1(1983).
[2] K.J. Eskola, K. Kajantie and K. Tuominen, Phys. Lett. B497, 39(2001).
[3] D. Kharzeev and E. Levin, Phys. Lett. B 523, 79(2001).
[4] I.G. Bearden et al., Phys. Lett. B523, 227(2001).
[5] I.G. Bearden et al., Phys. Rev. Lett. (2002).
[6] Zi-Wei Lin et al., Phys. Rev. C 64, 011902R(2001); and Zi-wei Lin,
private communication.

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