W. F. Fountain

Cosmic-ray proton and helium spectra: Results from the JACEE Experiment

Measurements of the cosmic-ray hydrogen and helium spectra at energies from 20 to 800 TeV are presented. The experiments were performed on a series of twelve balloon flights, including several long duration Australia to South America and Antarctic circumpolar flights. No clear evidence is seen for a spectral break. Both the hydrogen and the helium spectra are consistent with power laws over the entire energy range, with integral spectral indices 1.80 ± 0.04 and 1.68 -->+ 0.04−0.06 for the protons and helium, respectively. The results are fully consistent with expectations based on supernova shock acceleration coupled with a leaky box model of propagation through the Galaxy.

Energy spectra of cosmic rays above 1 TeV per nucleon

Direct measurements of cosmic-ray nuclei above 1 TeV/nucleon have been performed in a series of balloon-borne experiments with emulsion chambers. The observed all-particle spectrum above 20 TeV is consistent with the results of the Proton satellite and many air shower experiments. The proton spectrum is consistent with a power law having an index of 2.76 + or - 0.09 up to at least 100 TeV, but an overabundance of helium by a factor of 2 above 2 TeV per nucleon is found when compared with the extrapolation from the low energies. For heavy elements (C through Fe), the intensities around 1 TeV/nucleon are consistent, within the statistical errors, with the extrapolation from lower energy data using the Spacelab 2 spectral indices. An enhancement for the medium-heavy components (C through Ca) above 200 TeV is indicated. The mean mass above 50 TeV indicates slightly higher values than the results of the air shower experiments. 37 refs.

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.

Study of correlations of positive and negative charged particles

Abstract Particle correlations of the central collision events of 32 S + Pb at 200 GeV/AMU have been studied by utilizing a Magnetic-Interferometric-Emulsion-Chamber (MAGIC) detector. Particle angles, momentum, and charge-signs are measured for all produced charged tracks for each event. Two-particle correlation functions, C 2 = dN (¦ p 1 − p 2 ¦= q )/ dp 1 dp 2 , for (++), (−−) and (+-) particles are examined. A source radius around 4 – 6 fm is observed for overall identical particle correlations, while unexpected short-range correlations of unlike-sign pairs are observed in the high rapidity region. An analysis of unlike-sign pairs in terms of resonance decays indicated that a large amount (40% relative to pions) of η or ω mesons (decaying into 3 π), or of scalar iso-scalar σ mesons (decaying into 2π) would be required to explain some of the data. Multi-particle charge-sign clusters are recognized; however, their “run-test” and “conjugate-test” show small deviations from statistical fluctuations.

Rapidity and transverse momentum distributions in 6.4 TeV S+Pb interactions from CERN EMU05 experiments

Abstract Mixed transverse(P T ) momentum and rapidity distributions of charged particles produced in 200 GeV/AMU heavy ion collisions are obtained with Magnetic-Interferometric-Emulsion-Chamber ( MAGIC ) by CERN-EMU05 experiments. The P T spectra at different rapidity regions showed no anomalous enhancement of low P T components over a conventional, single exponential function with slope values ranging from 160 to 200 MeV/c.

Rapidity spacings and intermittency analyses by differenciating charge-sign in 200 GeV/amu S + Pb interaction from CERN EMU05 experiments

Fluctuations in rapidity are examined, by using CERN EMU05 experimental data differentiating charge-sign in S + Pb collision at 200 GeV/amu. Rapidity spacing analyses show limiting fluctuations at higher order spacings, while Poisson fluctuations are universally indicated in the lower spacings. The limiting behavior suggests that a long-range positive correlation, such as Wigner repulsion, is in order in the rapidity space. No clear evidence for the intermittent phenomena has been observed in the resultant normalized factorial moments in all charged, positively and negatively charged particles, respectively.

Transverse momentum distributions and particle correlations from EMU05

Abstract Transverse momentum distributions and multi-particle correlations of charged particles in 200 GeV/AMU heavy-ion collisions are studied with the Magnetic-Interferometricr-Emulsion-Chamber (MAGIC) for central collision events in 16 O + Pb and 32 S + Pb interactions. The P T distribution of negative-charged particles below 1 GeV/c fits a single exponential, while that of positive particles contains additional contributions of both highand low-P T particles. The like-sign, two particle correlations indicate HBT interferences, while that of the unlike-sign pairs possibly suggests other components. The apparent, multi-particle, charge-sign clustering is studied with the run-test and with Monte Carlo simulations. Some of the data are consistent with chance coincidence and the HBT interference.

Observation of early photon conversions in high‐energy cosmic‐ray interactions

High energy cosmic ray interactions were studied by the JACEE Collaboration using balloon‐borne emulsion chambers at high altitude. In high energy, yet low multiplicity interactions many secondary vertices were observed, probably due to decays of short‐lived particles. Early conversions of photons were found in the vicinity of these vertices. Conversion distances and angular distributions of the photons were studied.

Interpreting anomalous electron pairs as new particle decays

In heavy particle decays found in cosmic ray interactions recorded in the JACEE emulsion chambers, multiple electron pairs were previously reported. These pairs apparently originated from conversions of photons emitted in the decays. It is difficult to explain the overall properties of these decays in terms of known heavy particle decay modes. A recently published compilation of low-energy nuclear data suggests the presence of excess electron pairs with invariant mass of about 9 MeV/c2, which may be explained by postulating the existence of a new neutral boson decaying into the electron pair. The feasibility of explaining the JACEE electron pairs with this hypothesis is presented.