Baryon spectra in the low pT-region

The measurement of transverse momentum spectra for identified particle species in central collisions of relativistic heavy ions is of great interest for the determination of parameters which describe the phase of high density matter presumably formed in these collisions. If thermal equilibrium is reached in a heavy ion collision, then the transverse momentum distribution of the emitted particles is related to the freeze-out temperature T of the particle species under consideration. For a single source Boltzmann-distribution T would be obtained by fitting a distribution of the form A mT exp(-mT/T) to the measured transverse momentum spectrum, where mT=√m02 + pT2. An impressive sample of pT-spectra for different identified particles was recently measured at the AGS by the E802-group. The distributions of invariant cross sections for all measured particle species are in agreement with a Boltzmann-distribution as well as with an exponential distribution in the transverse mass mT. More interesting features of relativistic heavy ion collisions are possibly hidden in the very low pT-range. The measurements at 200 GeV/u at CERN revealed for π-spectra a deviation from the exponential slope, the so called 'low pT-enhancement,' below pT = 200 MeV/c. Many speculations about the origin of this phenomenon arose from these measurements down to very low values of pT. In this context it is therefore very interesting to measure spectra of nucleons in the same low pT region and search for similar enhancements. This paper discusses the search for these enhancements