Charged Particle Spectra in Sulfur + Sulfur Interactions at 200 Gev/nucleon from Ccd-Imaged Nuclear Collisions in a Streamer Chamber

We have measured the transverse momentum spectra 1/p_{T} dN/dp_{T } and rapidity distributions dN/dy of negatively charged hadrons and protons for central ^ {32}S + ^{32} S interactions at 200 GeV/nucleon incident energy. The data were taken using the streamer chamber of experiment NA35 at the CERN SPS but with a novel imaging and data acquisition system based on charge-coupled devices (CCDs) as image sensors. The negative hadron dN/dy distribution is too broad to be accounted for by thermal models which demand isotropic particle emission. It is compatible with models which emphasize longitudinal dynamics, by either a particle production mechanism, as in the Lund fragmentation model, or by introducing one-dimensional hydrodynamic expansion, as in the Landau model. The proton dN/dy distribution, although showing no evidence for a peak in the target fragmentation region, exhibits limited nuclear stopping power. We estimated the mean rapidity shift of participant target protons to be Delta y~ 1.5, greater than observed for pp collisions, less than measured in central pp collisions, and much less than would be observed for a single equilibrated fireball at midrapidity. Both the negative hadron and proton dN/dy distributions can be fit by a symmetric Landau two-fireball model. The negative hadron p_{T} distribution is independent of rapidity, suggesting that the underlying invariant cross section factorizes, Ed^3 sigma/d^3p=f(y)g(p_{T}). Although the spectrum possesses a two-component structure, a comparison to pp data at comparable center-of-mass energy showed no evidence for enhanced production at low p _{T} _sp{~} {<} 0.4 GeV/c. The two-component structure can be explained by a thermal and chemical equilibrium model which takes into account the kinematics of resonance decay. The proton p_{T} distribution, although showing a much higher mean p _{T} than in pp data < p_{T}>~ 0.600 GeV/c, is consistent with this model. Using an expression motivated by longitudinal expansion we found the same temperature for both the protons and negative hadrons at freezeout, T_{f}~ 170 MeV. We conclude that the charged particle spectra of negative hadrons and protons can be accommodated in a simple collision picture of limited nuclear stopping, evolution through a state of thermal equilibrium, followed by longitudinal hydrodynamic expansion until freezeout.