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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.
Production cross sections of K$^+$ and K$^-$ mesons have been measured in C+C collisions at beam energies per nucleon below and near the nucleon-nucleon threshold. At a given beam energy, the spectral slopes of the K$^-$ mesons are significantly steeper than the ones of the K$^+$ mesons. The excitation functions for K$^+$ and K$^-$ mesons nearly coincide when correcting for the threshold energy. In contrast, the K$^+$ yield exceeds the K$^-$ yield by a factor of about 100 in proton-proton collisions at beam energies near the respective nucleon-nucleon thresholds.
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.
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Production of charged kaons in proton-sulphur, proton-gold, sulphur-sulphur and oxygen-gold collisions at 200 GeV/nucleon has been studied in the NA35 Streamer Chamber experiment. Rapidity and transverse mass distributions as well as mean multiplicities were obtained. The results are compared with nucleon-nucleon data and with model predictions.
Product of charged kaons in central S + S and O + Au collisions at 200 GeV/nucleon has been studied in the NA 35 Streamer Chamber experiment. Mean multiplicities and transverse mass distributions were obtained. They were compared with nucleon-nucleon data and with model predictions.
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During the recent commissioning of Au beams at the Brookhaven Alternating Gradient Synchrotron facility, experiment 886 measured production cross sections for π±, K±, p, and p¯ in minimum bias Au+Pt collisions at 11.5A GeV/c. Invariant differential cross sections, Ed3σ/dp3, were measured at several rigidities (p/Z≤1.8 GeV/c) using a 5.7° (fixed-angle) focusing spectrometer. For comparison, particle production was measured in minimum bias Si+Pt collisions at 14.6A GeV/c using the same apparatus and in p+Pt collisions at 12.9 GeV/c using a similar spectrometer at KEK. When normalized to projectile mass, Aproj, the measured π± and K± cross sections are nearly equal for the p+Pt and Si+Pt reactions. In contrast to this behavior, the π− cross section measured in Au+Pt shows a significant excess beyond Aproj scaling of the p+Pt measurement. This enhancement suggests collective phenomena contribute significantly to π− production in the larger Au+Pt colliding system. For the Au+Pt reaction, the π+ and K+ yields also exceed Aproj scaling of p+Pt collisions. However, little significance can be attributed to these excesses due to larger experimental uncertainties for the positive rigidity Au beam measurements. For antiprotons, the Si+Pt and Au+Pt cross sections fall well below Aproj scaling of the p+Pt yields indicating a substantial fraction of the nuclear projectile is ineffective for p¯ production. Comparing with p+Pt multiplicities, the Si+Pt and Au+Pt antiproton yields agree with that expected solely from ‘‘first’’ nucleon-nucleon collisions (i.e., collisions between previously unstruck nucleons). In light of expected p¯ annihilation in the colliding system, such projectile independence is unexpected without additional (projectile dependent) sources of p¯ production. In this case, the data indicate an approximate balance exists between absorption and additional sources of antiprotons. This balance is remarkable given the wide range of projectile mass spanned by these measurements.
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