Emulsion Experiments Research Articles

Power-Spectrum Analysis of Fluctuations of Pseudorapidity Distributions in Nucleus-Nucleus Collisions at Very High Energies

Two events of ultrarelativistic nucleus-nucleus collisions observed in the Japanese-American cooperative emulsion experiment show large fluctuations of the pseudorapidity distributions of the charged secondaries. The fluctuations are analyzed by use of the power spectrum. A simulation is used to estimate the statistical noise. Fairly strong signals are found in the Si-AgBr event, while the Ca-C event exhibits only weak signals.

Counter experiments to search for anomalous particle fragments

We propose simple electronic counter experiments to test the existence and properties of anomalous particle fragments previously reported in emulsion experiments. We also suggest experiments to establish whether such phenomena extend to fragments in high energy elementary particle reactions.NUCLEAR REACTIONS Electronic counter experiments based on anomalous absorption suggested to study anomalous high energy nuclear fragments. Extension to particle physics.

Energy spectrum of cosmic ray primaries at super high energies estimated from the recent balloon-borne calorimeter measurements

The energy spectrum of primary cosmic ray particles has been estimated from the analysis of the chemical composition data of high energy cosmic rays, data obtained by the Japanese American cooperative emulsion experiments for proton and helium intensities and the Goddard Space Flight Centre measurements for cosmic ray nuclei. The results indicate no drastic change in abundance ratios at high energies. The elemental fluxes have been calculated by assuming that the primary cosmic ray nuclei break up into their constituent nucleons near the top of the atmosphere. The calculated total primary spectrum in the range 2–300 TeV follows the form N(E) dE = 2.24 × 104 E−2.7 dE where E is the energy expressed in GeV/nucleon and N(E) is the intensity expressed in (m2∙s∙sr∙GeV/nucleon) −1.Using this primary spectrum as the source of nucleons near the top of the atmosphere, the sea level proton and neutron spectra have been estimated by using the Feynman scaling hypothesis and the conventional nucleon-atmospheric diffusion equation. The derived spectra are in accord with the measured proton and neutron spectra of Brooke and Wolfendale, Ashton and Coates, and Ashton et al.

Projectile independence of normalized charged-particle multiplicity in hadron-nucleus collisions at energies ≥50 GeV

The normalized created-charged-particle multiplicity (${R}_{3}$) in hadron-nucleus interactions has been studied as a function of the effective number of projectile encounters calculated by using the additive quark model. The analysis of the $〈{\ensuremath{\nu}}^{\ensuremath{'}}〉$ data on the ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleus and $p$-nucleus interactions obtained from emulsion and counter experiments at energies \ensuremath{\ge}50 GeV suggests a new kind of scaling whereby the ${R}_{3}\ensuremath{-}〈{\ensuremath{\nu}}^{\ensuremath{'}}〉$ relationship is projectile independent.

Evidence for Anomalous Nuclei among Relativistic Projectile Fragments from Heavy-Ion Collisions at 2 GeV/Nucleon

Two independent emulsion experiments using Bevalac beams of $^{16}\mathrm{O}$ and $^{56}\mathrm{Fe}$ at \ensuremath{\sim}2 GeV/nucleon find with > 99.7% confidence that the reaction mean-free paths of projectile fragments, $3<~Z<~26$, 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.

Production of pions in heavy ion reactions below 500 MeV/nucleon

Pion production and subsequent absorption in heavy ion reactions at lab. energies 200–500 MeV/ N has been calculated using an independent nucleon-nucleon scattering description based on Glauber multiple scattering formalism, and a two step isobar model for pion absorption. Calculated pion production cross sections are compared to results from recent emulsion and streamer chamber experiments.

Corrections for target absorption of charged particles in wire loaded nuclear emulsions

In this paper we discuss how to correct multiplicities, angular and range distributions of charged particles in wire loaded emulsion experiments in order to make the results comparable to those of experiments where ordinary emulsions are used. The corrections arise from particles stopping in the wire or in a shadow zone around the wire and are of importance only for low energy particles. We suggest in the paper a function of the density, the charge and the diameter of the wire target to describe the multiplicity correction for black prong producing particles in hadron-nucleus and nucleus-nucleus reactions above 1 GeV/a.m.u.

Lifetimes and branching ratios for heavy-lepton cascades

We have advocated a heavy-lepton model in which the muonic sector ${M}^{\ensuremath{-}}$, ${M}^{0}$ explains neutrino-produced trimuons via cascade decay, and the electronic sector ${E}^{\ensuremath{-}}$, ${E}^{0}$ accounts for ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\mu}e+(\mathrm{missing}\mathrm{energy})$ events. For these heavy leptons we estimate lifetimes, expected track lengths in bubble-chamber and emulsion experiments, and branching ratios for all decay stages.

Computer simulations of cosmic-ray air showers II. Showers initiated by heavy primary particles

Computer simulations have been made of large extensive air showers initiated by nuclei heavier than protons. The work forms part of a study of future experiments designed to identify the nature of the energetic primary particles. A model based upon data from nuclear emulsion experiments has been used to represent the break-up of the primary nuclei in collision with air nuclei. Differences in shower characteristics are predicted which are dependent upon the choice of model for the fragmentation of the primary nucleus and its energy. The major cause of fluctuations in the longitudinal development of showers produced by heavy particles is shown to be the pattern of the fragmentation of the incident nucleus. In the absence of a precise knowledge of the high-energy interaction, we have not identified any parameter in large showers which, if measurable and averaged over many showers, will reflect strongly the nature of the primary particle.

Comment on two recent emulsion experiments related to scaling forE>1 TeV

Two recent papers report data which purport to cast doubt on the validity of «scaling» in inclusive strong interactions above one TeV. It is observed here that those two papers are in disagreement with each other more than with scaling. However, both sets of data are also shown to be not inconsistent with scaling after the inclusion of the experimental biases.

Scaling at very high energy and an emulsion experiment at the ISR

With reference to a recent paper of the Bombay-CERN-Cracow collaboration, we show that the ISR emulsion experiment does not disprove scaling.

The binding energy difference between the hypernuclides4HeΛ and4HΛ

Experimental and theoretical studies indicate a departure from charge symmetry for the mirror hypernuclides4HeΛ and4HeΛ amounting to a few tenths of a MeV in the binding energies. A nuclear emulsion experiment utilizing 45 newly measured π−-mesic decays of4HeΛ and4HΛ is reported to give ΔBΛ=BΛ(4HeΛ)-BΛ(4HeΛ)=(0.55±0.26)MeV. By adding events from the literature to this sample, a total of 214 π−-mesic decays of these hypernuclides was obtained. This number proved sufficient to resolve the difficulties previously encountered in an experimental evaluation of ΔBΛ. Contamination by other hypernuclides (probably5HeΛ) was eliminated from the4HeΛ sample by a strict recoil-range requirement (Rrec⩾10 µm), while, on the other hand, no contaminants were found among the4HeΛ decays. The binding energy discrepancy between the πr and πpr decays of4HeΛ was found to be due to pion range measurement losses which are important mainly for the πr events (Rπ∼4 cm). The final value of ΔBΛ for the latter sample is (0.30±0.15) MeV. Because a negative term in the theoretical calculation of ΔBΛ is expected from a Coulomb energy increase in the3He core of4HeΛ, this positive experimental result is a strong indication of charge-symmetry violation in the Δ Open image in new window interaction compatible with estimates of the virtual electromagnetic effects in (Λ→Λ+π0) suggested by theoretical workers.

The capture of K − mesons by complex nuclei

The effect on the two-nucleon capture process of nuclear and K − meson orbit distortion brought about by the residual Coulomb interaction is studied. It is suggested that a collective type of capture process by the distorted nucleus could exist which gives reasonable agreement with emulsion experiments without the assumption of surface α-particle clusters.

A 200 kG pulsed magnet for emulsion experiments

A pulsed magnet was constructed which will give a magnetic field of approximates 200 kgauss over a volume of approximates 120 cm/sup 3/ with a variation of less than 3% and almost constant during the time of a proton burst. The measurements and calculations are discussed with respect to the requirements, and possible improvements are proposed. (D.L.C.)

On some consequences of charge independence for K+-nucleon interactions

In the present work an attempt to find consistent relations between the three K+-N cross sections assuming the validity of charge independence is made. It is seen that, in this spirit, the K+-n elastic cross section should be much greater than previously deduced from counter and emulsion experiments. These experiments are then analysed and the possibility of increasing the value deduced from them for this cross section, bringing it in the limits required by charge independence, is shown to be consistent with reasonable changes of the parameters of the nuclear model used in the analysis of this interaction. Finally, a Tamm-Dancoff calculation in terms of pseudoscalar KNY coupling, taking into account the recoils, is made; a somewhat good fit with the experimental data is found, with values of the two coupling constantsgΣ andgΛ of the same order of magnitude as the π-N one.

Antiproton annihilations in complex nuclei

An investigation of 356 antiproton annihilations in nuclear emulsion is reported. The results are generally analysed to yield information on primary processes, assumed to be annihilations with single protons or neutrons into a number of pions with or without a K-meson pair. The average pion multiplicity is 4.68±0.12 for annihilations at rest, and 5.11±0.12 for annihilations in flight (the antiproton energy being on the average 166 MeV). This increase of 0.4±0.2 pions is to be compared with an expected average increase of 0.1 pion. The pion energy distributions are given with mean values of 391±10 MeV total energy (at rest) and 390±9 MeV (in flight). Emission of K-meson pairs is found to take place in 3±2% of the annihilation reactions. The average number of pions emitted together with K-mesons is 2.2±0.5. The correction for K-meson pairs unobservable in usual emulsion experiments has been computed. The result that about 40% of the K-meson pairs are undetectable, means that the correction for detection efficiency is larger than previously assumed. A recalculation of all published data using emulsion detectors results in a world average of 5.0±1.1% of the annihilations with K-meson pairs for annihilations at rest and in flight (antiproton energy below 250 MeV). The annihilation probability at rest with neutrons is found to be less than that with protons on the basis of a determination of the number of stars with an odd number of charged pions relative to that with an even number. The ratio odd/even is 0.73±0.09. The reabsorption probability of the pions in complex emulsion nuclei is determined. It is found that 18% of the pions are absorbed on the average (at rest) and 32% (in flight). The difference is understood as a result of the movement of the centre-of-momentum and the penetration of the antiprotons into the nuclei for the cases produced in flight. Comparison of our experimental results with the predictions of various theories is carried out. For the pion production, however, no decision in favour of a particular theoretical model can be made. As regards the production of K-mesons, all theories fail to predict the experimentally found production frequency. The world data on antiproton annihilations are collected, reanalysed and discussed.

Elastic Scattering of Low-EnergyK−Mesons on Protons

Low-energy K/sup -/-p elastic scattering events in bubble chambers and emulsions are studied in order to investigate the possibility of a peak at approximately 30 Mev. The results indicate that the scattering cross section is increasing in the region of lowest K/sup -/ meson momentum and that there is only approximately 1O% probability that the cross section will flatten off at momenta lower than 120 Mev/c. Possible explanations are offened for the cross-section flattening observed in earlier emulsion experiments. (D.L.C.)

Radiation measurements to 1500 kilometers altitude at equatorial latitudes

Three instrument packages containing Geiger tubes were flown into the inner Van Allen belt to altitudes up to 1500 km. Various absorber thicknesses were used to obtain range spectra for penetrating particles. Magnetic separation of electrons and protons was performed on counters with absorber thicknesses ranging from 1.7 mg/cm2 of mica to 36 mg/cm2 of aluminum. The electron spectrum observed with counters having electron energy thresholds of 30, 160, 190, and 460 kev appears considerably softer than a neutron beta-decay spectrum. Counts in counters with higher thresholds are assumed to be due to trapped protons and the measurements are compared with those obtained with nuclear emulsion experiments on similar trajectories. Absolute flux values are reported.

Low-Energy Antiproton Interactions in Hydrogen and Deuterium

The distributions of charged particles resulting from antiproton annihilations in hydrogen and deuterium are compared with the predictions resulting from the normalized statistical theory of Fermi. Multiplicities and momentum distributions are shown to be in agreement with the theory if the radius of the interaction volume is chosen to be about 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm. The values given for the average multiplicities observed in hydrogen and deuterium are 4.94\ifmmode\pm\else\textpm\fi{}0.31 and 5.03\ifmmode\pm\else\textpm\fi{}0.44, respectively, both somewhat lower than found in the emulsion experiments. $K$-meson production in annihilations was found to be consistent with previous experiments, but the number of events is statistically inadequate to warrant any new conclusions. The total elastic scattering cross sections in hydrogen, though of small statistical significance, are in agreement with recent theoretical calculations.

Monte Carlo Calculations on Intranuclear Cascades. II. High-Energy Studies and Pion Processes

The nuclear cascade calculations described in the preceding paper have been extended to incident energies up to 1.8 Bev with the inclusion of pion production, scattering, and absorption processes. Again the MANIAC electronic computer was used. Several incident proton energies between 450 Mev and 1.8 Bev have been investigated, with ${\mathrm{Al}}^{27}$, ${\mathrm{Cu}}^{64}$, ${\mathrm{Ru}}^{100}$, ${\mathrm{Ce}}^{140}$, ${\mathrm{Bi}}^{209}$, and ${\mathrm{U}}^{238}$ as target nuclei. Cascades initiated by pions of several energies up to 1500 Mev incident on ${\mathrm{Ru}}^{100}$ have also been studied. The elementary cross sections used and the assumptions made about details of the inelastic nucleon-nucleon and pion-nucleon processes are presented. The results of the calculation are summarized in tables and graphs giving data on transparencies, on numbers, energy spectra, and angular distributions of emitted cascade nucleons and pions, and on frequencies of occurrence and excitation energies of residual nuclei. The computed number distributions, energy spectra, and angular distributions of emitted particles are compared with the results of several emulsion experiments with incident protons and negative pions. The agreement is generally satisfactory, but certain discrepancies are found, for example regarding spectra and angular distributions of emitted pions; some of these discrepancies are discussed in terms of details of the model used. The calculation predicts quite well the over-all yield distribution of spallation products of copper produced by 2-Bev protons; however, as at lower energies, the calculated cross sections for ($p, \mathrm{pn}$) reactions are too low by factors of two or three.