The production of π±,K±,p has been measured in p+Be and p+Au collisions for comparison with central Si+Au collisions. The inverse slope parameters T0 obtained by an exponential fit to the invariant cross sections in transverse mass are found to be, T0p,K+,ππ∼140–160 MeV in p+A collisions, whereas in central Si+Au collisions, T0p,K+∼200–220 MeV >T0ππ∼140–160 MeV at midrapidity. The π± and K+ distributions are shifted backwards in p+Au compared with p+Be. A gradual increase of (dn/dy)K+ per projectile nucleon is observed from p+Be to p+Au to central Si+Au collisions, while pions show no significant increase.
Data on stable hadron production in p + p and p + n interactions at 200 GeV/ c are reviewed. Methods to construct missing data in the p + p, p + n, and n + n interactions are derived from charge symmetry and charge, baryon and strangeness conservation, and used to yield nucleon-nucleon interaction results. These may be useful for evaluating nucleus-nucleus collision measurements in terms of enhancements and suppressions. Parameterizations of p t 2 and rapidity distributions are presented to provide yields in acceptance cuts for comparisons to nucleus-nucleus data. As an example the derived nucleon-nucleon multiplicities are reduced to the acceptances of the NA-35 CERN S + S experiment.
Multiplicity distributions of negatively charged particles have been studied in restricted phase space intervals for central S+S, O+Au and S+Au collisions at 200 GeV/nucleon. It is shown that multiplicity distributions are well described by a negative binomial form irrespectively of the size and dimensionality of phase space domain. A clan structure analysis reveals interesting similarities between complex nuclear collisions and a simple partonic shower. The lognormal distribution agrees reasonably well with the multiplicity data in large domains, but fails in the case of small intervals. No universal scaling function was found to describe the shape of multiplicity distributions in phase space intervals of varying size.
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Measurements of charged particle multiplicity distributions in the central rapidity region in p-p and p-α, and α-α collisions are reported. They are better fitted to the “wounded nucleon” than to the “gluon string” model. The average transverse momenta, for all three reactions, are identical (and almost independent of multiplicity) up to very high multiplicities.
The neutral π0 and η mesons are studied in 197Au−197Au collisions at an incident energy of 800AMeV, substantially below the threshold for η production in N−N collisions. While the gross π0 multiplicity increases almost linearly with the number of participant nucleons, the multiplicities of η and hard π0 mesons show a stronger than linear dependence. The nonlinearity is governed by the average transverse-mass excess 〈mt〉−(s−2mN) of the mesons and is insensitive to their final-state interaction in the nuclear medium.
The production of neutral pions has been studied in the reactions 40 Ar + nat Ca , 86 Kr + nat Zr and 197 Au + 197 Au at 1 A GeV. For high energy pions emitted from the heavier systems a steeper than linear rise of the pion multiplicity with the centrality of the reaction is observed, indicating a pion production process other than binary nucleon-nucleon collisions. At low transverse momenta an enhancement of the π 0 -multiplicity increasing with the mass of the collision system is found. Systematic discrepancies between the experimental results and recent BUU, QMD and Cascade calculations are discussed.
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Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.
Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of \ee data. It is shown that certain aspects of the quarks emerging from within the proton in \ep interactions are essentially the same as those of quarks pair-created from the vacuum in \ee annihilation. The measured area, peak position and widthof the fragmentation function show that the kinematic evolution variable, equivalent to the \ee squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence effects in parton showers.
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