An article by Williams et al. fails to find evidence for critical behavior in central collisions of 35-400 MeV/nucleon Kr-84+Au-197. On, this basis, and because of the effect of secondary decay on the fragment charge distribution, these authors question the validity of the critical exponents obtained by the EOS Collaboration for 1 GeV/nucleon Au+C. It is shown that the experiment by Williams et nl. was not optimized to search for critical behavior and that the effect of secondary decay at the excitation energy corresponding to the critical point in the Au + C system is small. [S0556-2813(98)04612-3].

The impact parameter dependence of light charged particle (p,d,t,alpha) emission has been studied using an impact parameter selection based on coincident detection of residues or fission fragments. The energy spectra at twelve angles between 20 degrees and 150 degrees have been fit by a multiple moving source parametrization. The angle and energy integrated preequilibrium proton multiplicities decrease with increasing impact parameter in qualitative agreement with a Fermi jet calculation The preequilibrium d/p and t/p multiplicities increase slowly with increasing impact parameter and are nearly identical at the two bombarding energies. The preequilibrium alpha/p ratio shows a less consistent dependency on impact parameter but decreases significantly with increasing bombardment energy. A calculation of the d/p and t/p multiplicity ratios with a transport model incorporating complex particle emission is quite successful in reproducing the absolute magnitude, impact parameter dependence, and bombarding energy dependence of the experimental total multiplicities.

The dependence of intermediate-mass-fragment (IMF) element distributions on the multiplicity, N-IMF, of detected fragments has been measured for Kr-84+Au-197 collisions at E/A = 35, 55, 70, 100, 200, and 400 MeV. The observed dependence can be parametrized as P(N-IMF\Z)proportional to P(Z)exp(-c . N-IMF. Z), where c is a beam-energy and excitation-energy dependent parameter. Previous work indicated this parameter is zero in the liquid-gas coexistence region and positive in the gaseous phase. In contrast, we observe both negative and positive values for c, revealing the meaning of this parameter to be less straightforward than previously assumed. The magnitude of c appears nonetheless to provide a nontrivial test of multifragmentation models.

Differential cross sections for evaporation residues and fission fragments for 35A, 100A, 130A and 155A MeV $^{14}\mathrm{N}$ on targets ranging from $^{154}\mathrm{Sm}$ to $^{197}\mathrm{Au}$ have been measured. The angle-integrated cross sections are larger than what might be expected. The fission fragment-fission fragment folding angle correlations for 35A, 100A MeV $^{14}\mathrm{N}$ and 25A MeV $^{16}\mathrm{O}$ on similar targets were also measured. The average linear momentum transfer has been deduced from both the fission angle correlation and from the fore-aft asymmetry of the fission angular distributions in the laboratory system. The data are all consistent with a picture where pre-equilibrium particle emission removes an increasing fraction of the orbital angular momentum as the bombarding energy increases. This allows a large range of partial waves to contribute to formation of a composite nucleus with a finite fission barrier. \textcopyright{} 1996 The American Physical Society.

A set of compact ionization chamber-Si(IP)CsI(Tl) telescopes for multifragmentation studies are described. These ion chamber telescopes can be used either individually, or to augment the MSU Miniball 4π array. The characteristics of the large-area passivated, ion implanted Si detectors are investigated. Statistics on the overall planarity of these detectors as well as, the thickness of dead layers present at the surface of this type of detectors are examined.

The spatial-temporal extent of the emitting system for central collisions in Kr-84 + Au-197 at E/A = 35, 55, and 70 MeV is probed using fragment-fragment velocity correlation functions. Selection on fragment pairs of high velocity yields a stronger fragment-fragment Coulomb interaction than for inclusive fragment pairs. This result is consistent with fragment emission from a source of decreased spatial-temporal extent. The universality of this association and the effect of different selection criteria are explored. The sensitivity of the spatial-temporal extent deduced by the correlation function technique to measurement uncertainties, assumed source characteristics, and rotational effects is assessed.

Fragment emission patterns occurring in nuclear systems of modest excitation are studied. Exclusive measurement of fragment emission in 14N+197Au reactions at EA = 100, 130 and 156 MeV allows selection of central collisions where a single source dominates the decay. Low threshold measurement of IMF emission for these events allows investigation of the influence of detector threshold effects. The time scale of fragment emission is deduced using fragment-fragment velocity correlations. Comparisons are made to the predictions of a statistical decay model.

The relationship between observed intermediate mass fragment and total charged particle multiplicities has been measured for Kr-84 + Au-197 collisions at energies between E/A = 35 and 400 MeV. Fragment multiplicities are greatest for central or near-central collisions. For these collisions, fragment production increases up to E/A almost-equal-to 100 MeV, and then decreases at higher energies.

Highly fragmented exit channels produced by the decay of excited 24Mg projectiles were detected. The longitudinal velocity spectra of protons and alpha particles from such channels are offset. This offset is consistent with post-breakup Coulomb accelerations from the 197Au target nuclei implying that the protons were emitted within 3 X 10−22 s after the target-projectile separation.

The spatial and temporal extent of a system decaying by multifragment emission is deduced. Two-particle intermediate mass fragment correlation functions measured for central $^{36}\mathrm{Ar}$${+}^{197}$Au collisions at E/A=50--110 MeV indicate a rapid decay, 75 fm/c, of the highly excited system. Furthermore, the behavior of the correlation function at large relative velocities suggests that considerable charge loss occurs prior to fragment emission.

Transverse kinetic energy spectra of fragments in the reaction 36Ar + 197Au are used to probe the multifragmentation mechanism at intermediate energies. The mass dependence of the average transverse kinetic energy is examined in the context of the statistical decay of an expanding, emitting source. The role of source expansion during emission is explored. Results suggest the onset of volume emission at the highest incident energy.

Measurements of the response of the participant calorimeter to 250–400 MeV/c π+, μ−, and e+ are described. The participant calorimeter is a Pb/Fe/scintillator sampling calorimeter with a novel wavelength shifting fiber optic readout which is used in experiment 814 at Brookhaven National Laboratory. The e+/π+ response ratio at 250–400 MeV/c is larger than it is at higher momenta. Previous measurements of the e/π response ratio with sampling calorimeters found that the value decreased as the particle energies were reduced below about 1 GeV. This difference is attributed to the different absorption probabilities for π+ and π− at low momentum.

Recent results from the E814 collaboration are presented for reactions of 14.6 GeV/nucleon 28Si projectiles with targets of Al, Cu, and Pb. This includes transverse energy distributions over the full solid angle and the distribution of charged particle multiplicity in the forward hemisphere. Furthermore we present recent results on transverse momentum spectra and rapidity distributions for protons and discuss them in terms of stopping and/or transparency. A fraction of nucleons emerges at beam rapidity, even for the most central collisions. These ‘punch-through’ distributions are shown to yield information on the in-medium nucleon-nucleon cross section. Finally, we discuss antiproton production at 0° as a function of event centrality to shed some light on possible reabsorption.

We have used the E814 apparatus to make a systematic study of antiproton production in collisions of 28Si ions at 14.6 GeV/c per nucleon with targets of Pb, Cu, and Al. We have measured the antiproton yield per interaction as a function of transverse energy and have found the yield to increase by a factor of ≈ 2 in going from the least to the most central collisions on the Pb target. A simple first-collision picture of antiproton production predicts the yield to increase by a factor of ≈ 11. We suggest that the discrepancy may result from the annihilation of antiprotons within the nuclear medium.

Transverse momentum distributions of light mass beam rapidity fragments 1H, 3He, and4He in reactions of 28Si + Al, Cu and Pb are presented. The widths of the distributions are found to increase with increasing projectile-target overlap. This dependence is not consistent with the observed distributions being associated with the Fermi momentum of the nucleons in the projectile nucleus.

The Participant Calorimeter for Experiment 814 at BNL is a lead-scintillator sampling calorimeter. The response of the calorimeter to beams of e, μ, π and p from 1.56 to 6.8 GeV/c is presented. The design and performance of two gain monitoring systems are described, one system measures the response of single scintillator plates in the calorimeter. The calorimeter electromagnetic energy resolution varies from 24 to 32%√E for different towers. For hadron energies over 5 GeV the σh/E = 43±3%/√E, and e/h = 1.02±0.07.

A Pb/scintillator sampling calorimeter covering the pseudorapidity interval of η = 0.83 to 4.20 has been designed and constructed for Experiment 814 of Brookhaven National Laboratory. The calorimeter uses wavelength shifting optical fibers for readout. Such fibers allow the construction of a highly granular and longitudinally compact device. A novel scheme for coupling a fiber to a scintillator plate has been designed that yields a high photoelectron response. Longitudinally, the calorimeter has a depth of four interaction lengths divided into two electromagnetic sections and two hadronic sections of 0.4, 0.4, 1.6, and 1.6 interaction lengths, respectively.