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The slow, target associated particles produced in ultrarelativistic heavy-ion interactions are a quantitative probe of the cascading processes in the spectator parts of the target nucleus. These processes are directly influenced by the proper timescale for the formation of hadronic matter. In this letter we show experimental data on singly and multiply charged particles, with velocities smaller than 0.7 c , produced in ultrarelativistic heavy-ion interactions in nuclear emulsion.

The average multiplicities of singly charged relativistic particles in oxygen-induced interactions with a nuclear emulsion target are studied over the energy range 2.1–200 A GeV. A similar energy dependence as for proton-induced interactions is observed. Both the number of participating nucleons and the number of binary collisions are shown to be of importance for the particle production.

Two independent emulsion experiments using Bevalac beams of {sup 16}O and {sup 56}Fe at {approx}2 GeV/nucleon find with > 99.7% confidence that the reaction mean-free paths of projectile fragments, 3 {approx}< Z {approx}< 26, are shorter for a few centimeters after their emission than at larger distances, or than predicted from experiments on beam nuclei. This effect, which is enhanced in later generations of fragments, can be interpreted by the relatively rare occurrence of fragments that interact with an unexpectedly large cross section.

Proton-nucleus interactions have been studied in nuclear emulsion exposed to the NAL 200 GeV proton beam. The inelastic mean free path is found to be 35.5 ± 0.8 cm and the average shower particle multiplicity is 12.9 ± 0.2. The angular distribution reveals some characteristics features of proton-nucleus interactions.

We present the results of 1179 precise charge measurements carried out on 1 ⩽ Z ⩽ 3 projectile fragment nuclei from relativistic nucleus-nucleus collisions in nuclear emulsion. We find no evidence for the existence of third-integral fractionally charged projectile fragments, particularly for those with charges 5 3 and 7 3 .

An exclusive-type study of the transverse momentum distribution of alpha particles emerging as relativistic projectile fragments from collisions of a 1.9 GeV/nucleon 56Fe beam in nuclear emulsion reveals that the events fall into either one or the other of two distinct classes with sharply differing characteristics. Each of these classes is characterised by a Maxwellian distribution in the projectile rest frame, but the associated temperatures differ by a factor of about four (namely approximately=10 MeV and approximately=40 MeV; the same 40 MeV temperature is observed among target-related alpha particles emitted from 12C collisions in nuclear emulsion at 0.87 GeV/nucleon and 2.1 GeV/nucleon). The authors show that the 'hot' (T approximately=40 MeV) events are not simulated by 'projectile bounce' effects, and that they occur among events of high multiplicity as well as among those of low multiplicity. They are regarded as direct evidence for a highly collective mechanism.

Two consequences of coherence of mesonic fields have been tested in proton-nucleus collisions. Multiplicity fluctuations measured in finite rapidity intervals are found to obey a Poisson distribution at large rapidities where nuclear transparency occurs. In close analogy to quantum optics we present a quark-parton model in which this link between coherence and transparency is realized via the phenomenon of self-induced transparency.

Here we present results on charged hadron production in an experiment using tracking detectors with the highest possible spatial resolution: emulsion chambers. A sample of the most central collisions will be compared to the predictions of the Lund Model, which does an accurate job of representing conventional (non−quark−gluon plasma) physics in nuclear reactions. We can use the high resolution of our detectors to examine spatial correlations in several ways. In particular, the radial size of the particle formation region can be estimated using pion interferometry techniques. (AIP)

Pseudorapidity distributions of relativistic singly charged particles in oxygen-induced emulsion interactions at 14.6, 60, and 200 GeV/nucleon are studied. Limiting fragmentation behavior is observed in both the target and projectile fragmentation regions for a central as well as for a minimum-bias sample. Comparisons with the fritiof model reveal that the picture of fragmenting strings successfully describes the observed data.

Experimental studies of the interactions between nuclei at relativistic energies had their beginnings with the momentous discovery of the existence of the heavy-ion component of the primary cosmic rays in 1948 by Freier et. al. (Fr 48,48a). Because of the broad energy spectra of the cosmic rays, highly relativistic nucleus-nucleus collisions, with abundant particle production, were observed in these early experiments. Also, it was realized that complementary investigations on the elemental and isotopic abundances of the heavy-ion component would have profound astrophysical implications.

Annihilation of heavy'' antinuclei, such as {ital {bar d}}, {ital {bar t}}, or {bar {alpha}} in nuclear matter could serve to probe whether the constituent antinucleons annihilate independently of each other or whether a single fireball is formed. In the latter case the total meson multiplicity distribution should have a lower mean and a larger relative width than in the trivial case. The meson spectrum would be correspondingly harder.

The authors defend their two-component convolution model to descibe multiplicity distributions of hadron-hadron interactions. (AIP)