A. Medvedev

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.

Strange meson enhancement in PbPb collisions

Abstract The NA44 Collaboration has measured yields and differential distributions of K + , K − , π + , π − in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/ c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K + production per π is observed, as compared to p + p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.The NA44 Collaboration has measured yields and differential distributions of K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K+ production per pi is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.

One and two-dimensional analysis of 3π correlations measured in Pb+Pb interactions

Abstract π−π−π− correlations from Pb+Pb collisions at 158 GeV/c per nucleon are presented as measured by the focusing spectrometer of the NA44 experiment at CERN. The three-body effect is found to be stronger for Pb+Pb than for S+Pb. The two-dimensional three-particle correlation function is also measured and the longitudinal extension of the source is larger than the transverse extension.

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.

Directional dependence of the pion source in high-energy heavy-ion collisions

Abstract π + π + and π − π − correlations from 200 GeV per nucleon S + Pb collisions and π + π + correlations from 450 GeV p + Pb collisions measured by the focussing spectrometer of CERN experiment NA44 are presented. The large data set which emphasizes small values of momentum difference allows multi-dimensional analysis along with the more traditional one-dimensional parameterization to characterize the pion emission source. It is found that the three radius parameters are similar and large compared to the projectile radius. This can be explained by pion scattering in the final state hadronic system.

Kaon interferometry in heavy ion collisions at the CERN SPS

K+K+ and K−K− correlations from S+Pb collisions at 200 GeV/c per nucleon and K+K+ correlations from p+Pb collisions at 450 GeV/c per nucleon, are presented as measured by the focusing spectrometer of the NA44 experiment at CERN. Multidimensional fits are performed in order to characterize the kaon-emission volume, which is found to be smaller than the pion-emission volume.

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.

Two-proton correlations near midrapidity in p+Pb and S+Pb collisions at the CERN SPS

Correlations of two protons emitted near midrapidity in p+Pb collisions at 450 GeV/c and S+Pb collisions at 200A GeV/c are presented, as measured by the NA44 Experiment. The correlation effect, which arises as a result of final state interactions and Fermi-Dirac statistics, is related to the space-time characteristics of proton emission. The measured source sizes are smaller than the size of the target lead nucleus but larger than the sizes of the projectiles. A dependence on the collision centrality is observed; the source size increases with decreasing impact parameter. Proton source sizes near midrapidity appear to be smaller than those of pions in the same interactions. Quantitative agreement with the results of RQMD (v1.08) simulations is found for p+Pb collisions. For S+Pb collisions the measured correlation effect is somewhat weaker than that predicted by the model simulations, implying either a larger source size or larger contribution of protons from long-lived particle decays.Abstract Correlations of two protons emitted near midrapidity in p + Pb collisions at 450 GeV/ c and S + Pb collisions at 200 A GeV/ c are presented, as measured by the NA44 Experiment. The correlation effect, which arises as a result of final state interactions and Fermi-Dirac statistics, is related to the space-time characteristics of proton emission. The measured source sizes are smaller than the size of the target lead nucleus but larger than the sizes of the projectiles. A dependence on the collision centrality is observed; the source size increases with decreasing impact parameter. Proton source sizes near midrapidity appear to be smaller than those of pions in the same interactions. Quantitative agreement with the results of RQMD (v1.08) simulations is found for p + Pb collisions. For S + Pb collisions the measured correlation effect is somewhat weaker than that predicted by the model simulations, implying either a larger source size or larger contribution of protons from long-lived particle decays.

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.

Charged hadron distributions in pA and AA collisions at the CERN SPS

Abstract Single particle distributions of π ± , K ± , p , p and d near mid-rapidity from 450 GeV/c p A and 200 GeV/c per nucleon SA collisions are presented. Inverse slope parameters are extracted from the transverse mass spectra, and examined for indications of collective phenomena. Proton and antiproton yields are determined for different projectile-target combinations. First results from 160 GeV/c per nucleon PbPb collisions are presented.