W. V. Jones

JACEE emulsion chambers for studying the energy spectra of high energy cosmic ray protons and helium

Abstract Emulsion chambers are being used in a series of stratospheric balloon flights to study nuclear interactions, charge composition, and energy spectra of cosmic ray nuclei over the energy range 10 12 –10 15 eV. Charge identification involves grain, gap, and/or delta-ray counting in emulsion plates having different sensitivities on two sides of an acrylic base. Electromagnetic cascade energies are measured with resolutions of about 25% by the three-dimensional track counting method. This report describes the apparatus, the measurement techniques, and the analysis methods used to determine the primary proton and helium spectra.

Multiplicity in proton-nucleus interactions in emulsion at 800 GeV

The experimental data on multiplicities of charged particles of different type produced in incoherent interactions of 800 GeV proton with emulsion nuclei are reported and discussed. The data are compared with the results of other experiments on protonnucleus collisions at lower energies. It is shown that the Lund model describes well the data on multiplicities of relativistic particles.

Interactions of 10.6 GeV/nucleon gold nuclei in nuclear emulsion

Stacks of nuclear emulsion were exposed at the Brookhaven AGS to a 10.6 GeV/n beam of gold nuclei in the BNL 868 experiment. A preliminary analysis of the main features of the interactions of these nuclei is reported here and compared with those observed previously at lower energies,E<1 GeV/n. The multiplicity and pseudo-rapidity distributions of the singly charged particles emitted both in central and in minimum bias samples of interactions have been analyzed in order to look for any non random effects indicative of the nuclear state during the interactions. The fragmentation characteristics of the gold projectiles appear to be different at 10.6 GeV/n from those at ≦1 GeV/n incident energy. Fission of the gold projectiles, which was relatively frequent at low energy, is almost entirely suppressed. Some of alpha particles from the projectile are emitted with very large transverse momenta. In gold-emulsion interactions the residual target nuclei are significantly smaller than in oxygen and sulfur interactions in emulsion.

Direct measurement of the composition and spectra of cosmic rays above 1 TeV/amu from Jacee

Abstract Direct measurements on cosmic ray protons through iron above about 1 TeV/amu have been performed in a series of balloon-borne experiments with emulsion chambers. The measured energy spectra of protons and helium are power laws with exponents of 2.77 ± 0.09 and 2.72 ± 0.11 in the energy range 5 to 500 TeV and 2 to 50 TeV/amu, respectively. The proton spectrum shows no evidence of the steepening near 2 TeV which was reported by other experiments. Helium has a slightly higher intensity compared to extrapolations from lower energy measurements. The heavier elements, carbon to sulfur, show a small tendency for intensity enhancement in the relative abundance above 10 TeV/amu.

Cosmic ray results from the jacee experiments

Abstract Studies of high-energy nucleus-nucleus interactions with balloon-borne JACEE emulsion chambers are summarized. High energy, high multiplicity interactions are found with high-energy-density (⩾ 2 GeV/fm3), high observed values (500 – 2,000 MeV/c), and several interesting pseudorapidity and/or azimuthal structures. Very short-range correlations of charged particles, and several other inclusive characteristics are discussed.

Evidence for a nuclear phase transition in target nuclei after relativistic nuclear interactions

The degree of excitation of the emulsion target nuclei due to nuclear interactions of oxygen and sulfur projectiles at 200 GeV/nucleon incident energy has been investigated. Using the plausible assumption that the numberNb of slow particles emitted from the struck target nucleus can be interpreted as a measure of the temperatureT of the residual nucleus, we have found that there exists a critical temperatureTc of the excited target nucleus. For Ag and Br target nuclei this temperature corresponds to ≌12 and it is attained when the impact parameters are less than about 4 fm.

Interactions of 10.6 GeV/n gold nuclei with light and heavy target nuclei in nuclear emulsion

We have investigated the particle production and fragmentation of nuclei participating in the interactions of 10.6 GeV/n gold nuclei in nuclear emulsions. A new criterion has been found to distinguish between the interactions of these gold nuclei with the light (H,C,N,O) and heavy (Ag, Br) target nuclei in the emulsion. This has allowed separate analyses of the multiplicity and pseudo-rapidity distributions of the singly charged particles emitted in Au-(H,C,N,O) and Au-(Ag,Br) interactions, as well as of the modes of breakup of the projectile and target nuclei. The pseudo-rapidity distributions show strong forward asymmetries, particularly for the interactions with the light nuclei. Heavy target nuclei produce a more severe breakup of the projectile gold nucleus than do the lighter targets. A negative correlation between the number of fragments emitted from the target nuclei and the degree of centrality of the collisions has been observed, which can be attributed to the total destruction of the relatively light target nuclei by these very heavy projectile nuclei.

High energy cosmic ray events of ultra-relativistic nucleus-nucleus collisions☆

Abstract Cosmic ray ultra-relativistic nucleus-nucleus collision events in the TeV/A region are analyzed. The average transverse momentum of non-peripheral events is examined and the breakdown of the limiting behaviour of this quantity is observed in events with high energy density. Close pairing or clustering of tracks is observed in many events. Possible explanations of the phenomena are discussed.

COHERENT PRODUCTION OF PARTICLES IN INTERACTIONS OF 800 GEV PROTONS WITH EMULSION NUCLEI

The experimental data on total and topological cross sections for coherent diffractive dissociation of 800 GeV protons on emulsion nuclei are presented. The energy dependence of basic characteristics of these reactions is discussed.

New event types in a balloon‐gorn cosmic ray experiment

Proton‐nucleus interactions at the mean energy of about 45 TeV and nucleus‐nucleus interactions at energies greater than 1 TeV/nucleon are being studied with a balloon born emulsion chamber. The multiplicities of charged secondaries, the fractional energy spectra and transferse momentum distribution of gamma rays, and the rapidity density in the central region are obtained. The features of inelastic proton‐nucleus interactions are as expected from extrapolations of measurements at lower energies. On the other hand, preliminary data on nucleus‐nucleus interactions indicate some features not expected by simple superposition of nucleon‐nucleon interactions. Examples of unusual phenomena include one event with multiplicity Ns=1000 and several events with apparent high PT particle productions.