The production of pions, protons and deuterons is studied at a laboratory angle of 144° in
28Si+Pb collisions at 14.6 GeV/
c per nucleon. The centrality dependence of the pion yields is studied over ...the full impact parameter range using a zero degree calorimeter. The results are compared with the hadronic cascade model RQMD. These calculations are generally in agreement with the experimental results. According to these calculations, the pion yield in our acceptance is completely dominated by Δ-decay at freeze-out. Our measurements thus support the importance of baryon resonance production as one of the central features of relativistic heavy ion collisions at AGS energies. Although the strength of the pion spectrum is adequately described for kinetic energies above 50 MeV, an additional very soft component is observed in the pion spectra which is not predicted by RQMD. This very soft component accounts for a significant fraction of the total pion yield in this rapidity range but remains unexplained.
Collisions of {sup 28}Si+Al, Cu, Pb at {ital E}{sub lab}/{ital A}=14.6 GeV were studied in a calorimetry-based experiment at the BNL Alternating Gradient Synchrotron. Transverse-energy production was ...measured for pseudorapidities {minus}0.5{lt}{eta}{lt}0.8. Correlations with the spectra and multiplicity of neutrons and protons emitted into a forward 0.8{degree} cone demonstrate quantitatively the large amount of nuclear stopping observed in these reactions. Calculations in hadronic-fireball or nucleon-nucleon based models underpredict the measured transverse-energy production for Si+Pb and indicate the need to include rescattering of secondaries and /or contributions from target fragmentation.
We have studied in detail the electromagnetic dissociation of sup 28Si projectiles at 14.6 GeV/(ital c nucleon), interacting with Pb, Sn, Cu, and Al targets. Exclusive cross sections were measured ...for several decay channels, including final states involving the emission of protons, neutrons, and alpha particles. Excitation energy distributions for the 1ital n+sup 27Si and 2ital p+sup 26Mg decay channels were reconstructed with a resolution of 2 MeV, using a constrained kinematic fit. The energy distributions obtained for 1ital n+sup 27Si are in good agreement with the sigma(gamma,ital n) photoneutron cross sections multiplied by the virtual photon spectrum obtained in the Weizsaecker-Williams approximation. A search for the double photon excitation process, based on the dependence of the cross sections on the target atomic number, was performed.
Collisions of {sup 28}Si+Al, Cu, and Pb at {ital E}{sub lab}=14.6 GeV/nucleon were studied at the Brookhaven National Laboratory Alternating Gradient Synchrotron. Charged particle multiplicity was ...measured over the pseudorapidity interval 0.875{le}{eta}{le}3.86 with a silicon pad detector. A strong correlation is seen between the multiplicity and the transverse energy measured in the interval {minus}0.5{le}{eta}{le}0.8. Correlation with the energy going forward after the collision and comparison with calculations indicate that rescattering is required to explain the data. The data are compared under the assumption of Koba-Nielson-Olesen scaling. The measured multiplicity scales approximately with the total number of participant nucleons and less well with the available center-of-mass kinetic energy.
We report a direct measurement of the final-state energy spectrum in the electromagnetic dissociation of {sup 28}Si into {ital p}+ {sup 27}Al at an energy of 14.6 GeV/nucleon. The final-state energy ...is obtained through a calculation of the {ital p}-{sup 27}Al invariant mass in kinematically reconstructed events. The final-state energy spectrum for all targets is peaked near the isovector giant-dipole resonance in {sup 28}Si and the dependence of the magnitude of the cross section on target charge confirms that the excitation is largely electromagnetic. By exploiting the expected scaling behavior on target {ital Z} and {ital A}, the background from nuclear interactions is evaluated and subtracted, leaving a pure electromagnetic dissociation final-state energy distribution. This distribution is well reproduced by simulated events, in which the photon spectrum calculated in the Weiszaecker-Williams approximation is combined with experimental data on the photonuclear reaction {sup 28}Si({gamma},{ital p}) {sup 27}Al, and slight differences are observed only at low final-state energy.
Electromagnetic dissociation cross sections for one, two, and three nucleon removal were measured for an {ital E}{sub lab}/{ital A}=14.6 GeV {sup 28}Si beam impinging on {sup 27}Al, {sup 120}Sn, and ...{sup 208}Pb targets. The measured cross sections exhibit an approximate {ital Z}{sub {ital T}}{sup 2} dependence and are well reproduced by calculations convoluting the virtual photon spectrum with the experimental {sigma}({gamma},{ital N}) photonuclear cross sections. Comparison with other experimental results and energy dependence of the cross sections are discussed.
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