M. Kopytine

Mid-rapidity protons in 158A·GeV Pb+Pb collisions

Abstract Proton distributions at mid-rapidity (2 ≤ y ≤ 3) have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. From baryon number conservation and by comparing the experimentally measured d N d y distribution with the transport model RQMD, we conclude that a rather high degree of nuclear stopping has been reached for the truly heavy-ion collisions at these energies. Transverse mass distributions exhibit characteristically thermal shapes and the slope parameters increase with the mass of the colliding system.

Coulomb effect in single particle distributions

Abstract Single particle distributions from heavy-ion collisions show the effect of Coulomb interactions on the final state. While a rather strong effect is seen in the ratio π − π + from central 158A·GeV/c Pb+Pb collisions, at most a small enhancement is found in the ratios from S+S and S+Pb collisions at 200A·GeV/c.

Particle ratios from central Pb + Pb collisions at the CERN SPS

We will address the physics of K?/K+ and /p ratios measured in 158 A GeV Pb + Pb collisions as a function of centrality and transverse momentum. We observe little significant centrality dependence in neither K?/K+ nor /p ratios and they are almost constant as a function of PT. In addition to the chemical freeze-out temperature Tch, we extract the chemical potentials for both light and strange quarks (?q and ?s) by comparing the present data with simple model predictions. Tch is greater than the thermal freeze-out temperature which is extracted from the transverse momentum distribution of charged hadrons.

Measuring the space-time extent of nuclear collisions using interferometry

Abstract Hanbury-Brown and Twiss (HBT) interferometry is used to study the space-time evolution of nuclear collisions at CERN energies. Pairs of identified pions, kaons and protons are studied by NA44 for a variety of collisions systems ranging from p-Pb to Pbue5f8Pb. The pion and kaon correlation data from the 1994 and 1995 Pb runs are compared to published data. The systematic increase in radius parameter with system size is continued in the Pb data sample. Model comparision stress the importance of scattering in the evolution of the collision.

Deuteron and triton production in Pb+Pb collisions at 158 A·GeV.

Abstract NA44 has measured the invariant cross section of deuterons and tritons at non zero p t in 158 A·GeV lead on lead collisions at CERN SPS. Normalized transverse mass spectra and coalescence parameters versus p t have been calculated showing a significant transverse flow. Radius parameters have been extracted using a simple thermal coalescence model. Results from RQMD+coalescence calculations are compared to the data.

Two kaon correlations from Pb+Pb collisions at 160 AGeV from NA44

Abstract K+K+ correlations from Pb+Pb collisions at the CERN experiment NA44 will be presented. NA44 is a focussing spectrometer that uses the 160 AGeV Pb beam at the SPS and specializes in the detection of a few artices near mid-rapidity. A comparison of the results from pion and kaon correlations will be made, and the mt dependence of hadron correlations will also be discussed.

Coalescence, interferometry and flow

Abstract NA44 has measured proton and deuteron distributions from SS and SPb collisions at 200 GeV/ c and PbPb collisions at 158 GeV/ c . The mean p T of both protons and deuterons grows with system size but the deuterons are somewhat slower than the protons. The phase space density of protons falls with m T but increases for larger systems. The phase space density of p s is much lower than of protons while their average freeze-out radii are similar. The proton source size increases with system size but not as rapidly as the pion source. For PbPb collisions, all radii lie on a single curve.