N. Maeda

Identified pion interferometry in heavy-ion collisions at CERN

Abstract π + π + correlations from S + Pb collisions at 200 GeV/ c per nucleon, measured by the focusing spectrometer of the NA44 experiment at CERN, are presented. The large data set, particularly at small values of Q inv , allows determination of the detailed shape of the correlation function. We construct the background by event mixing, and correct for resolution, Coulomb interaction, and distortion of single-particle spectra which produce effects large compared to the statistical errors at small Q inv . An exponential, rather than gaussian, source distribution is slightly favoured, but both are statistically acceptable.

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.

Three Pion Correlations in Sulphur Lead Collisions at the CERN SPS

Abstract π + π + π + correlations from sulphur-lead collisions at 200 GeV/c per nucleon are presented as measured by the focusing spectrometer of experiment NA44 at CERN. We have investigated the three-pion correlation function at mid-rapidity and found that a genuine three-body correlation is suppressed. A possible interpretation of this result is that the emission of particles is partially coherent.

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.

A Cherenkov beam counter for ultra-relativistic heavy-ion experiments

Abstract A beam counter system consisting of two sets of gas Cherenkov counters was constructed for ultra-relativistic heavy-ion experiments. The performance has been examined with sulphur ions of 200 GeV/c per nucleon. The intrinsic time resolution and the width of the pulse height distribution are 30 ps and 5%, respectively, at a beam intensity of 2×106 ions/s. The detector was successfully operated for more than one month, although some reduction in pulse height was observed as a long-term variation.

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.

Charged kaon and pion production at midrapidity in proton-nucleus and sulphur-nucleus collisions

The NA44 collaboration has measured charged kaon and pion distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450 GeV/c per nucleon, respectively. The inverse slopes of kaons are larger than those of pions. The difference in the inverse slopes of pions, kaons and protons, all measured in our spectrometer, increases with system size and is consistent with the buildup of collective flow for larger systems. The target dependence of both the yields and inverse slopes is stronger for the sulphur beam suggesting the increased importance of secondary rescattering for SA reactions. The rapidity density, dN/dy, of both K+ and K- increases more rapidly with system size than for pi+ in a similar rapidity region. This trend continues with increasing centrality, and according to RQMD, it is caused by secondary reactions between mesons and baryons. The K-/K+ ratio falls with increasing system size but more slowly than the pbar/p ratio. The pi-/pi+ ratio is close to unity for all systems. From pBe to SPb the K+/p ratio decreases while K-/pbar increases and ({K+*K-}/{p*pbar})**1/2 stays constant. These data suggest that as larger nuclei collide, the resulting system has a larger transverse expansion, baryon density and an increasing fraction of strange quarks.