Search Results (6 total)

Transverse momentum spectra of η mesons have been measured near the free nucleon-nucleon production threshold in the heavy ion reactions ⁴⁰Ar+ ^natCa, ⁸⁶Kr + ^natZr, and ¹⁹⁷Au+ ¹⁹⁷Au at 1.0A GeV and also in ⁴⁰Ar+ ^natCa at 1.5A GeV. The measured transverse momentum distributions are compared to model calculations. The relative abundance of Δ(1232) and N(1535) resonances excited in the collision is deduced. A comparison to pion data reveals scaling with the transverse mass of the emitted meson.

The multiplicities of p and α particles detected in coincidence with fragments emitted in fully relaxed collisions in the reactions of 18.5A MeV ¹³⁶Xe+⁴⁸Ti have been measured for different exit channel mass asymmetries. A kinematic source analysis of the spectra and angular distributions of the light particles has been used to separate the total multiplicities into prescission and postscission contributions. From these results, the excitation energies at scission are determined using an empirical technique based upon previous measurements of light charged particle multiplicities observed in coincidence with evaporation residues. These excitation energies are found to decrease from ∼400 MeV to 110 MeV as the fragment mass asymmetry, A_H/A_L, varies from 4.8 to 1.0. A corresponding increase of the mean lifetime of the scissioning nucleus from ∼5×10^-22 s to ∼1×10^-20 s is derived using calculated statistical model decay widths. The extent to which this variation of lifetime with mass asymmetry may be attributed to completely damped deep inelastic collisions or to dynamic delays in the decay of a compound nucleus is discussed as is the need for inclusion of dynamics in the deexcitation calculations for hot nuclei. Observed three fragment events are also discussed.

The azimuthal angle distributions of neutral pions at midrapidity from Au+Au reactions at 1 GeV/nucleon incident energy have been measured. An enhanced emission of π⁰’s perpendicular to the reaction plane is observed. The azimuthal asymmetry is dependent on the π⁰ momentum: the π⁰ spectrum perpendicular to the reaction plane is harder than in the reaction plane. The strength of the observed asymmetry appears to be more pronounced for π⁰ than for charged particles and neutrons.

The photon decay of the relativistic Coulomb excitation of the single and double giant dipole resonance (GDR) in the target has been observed in the system 1A GeV ²⁰⁹Bi on ²⁰⁸Pb. For peripheral events which are dominated by relativistic Coulomb excitation, a large Lorentzian structure in the photon energy spectrum is peaked at 13.3±0.1 MeV with a width of 4.1±0.1 MeV, corresponding to the single GDR in the ²⁰⁸Pb target. The sum energy of coincident γ-γ pairs shows a broad feature at 25.6±0.9 MeV with a Lorentzian width of 5.8±1.1 MeV, which we assign to the double GDR observed via the two-γ decay channel.

High-energy γ rays have been measured in coincidence with heavy fragents in deeply inelastic reactions of ¹³⁶Xe+⁴⁸Ti at 18.5 MeV/nucleon. The giant dipole resonance (GDR) strength function is deduced from an analysis of the photon spectra within the statistical model. The GDR width Γ is studied as a function of the fragment excitation energy E^*. A saturation at about Γ=10 MeV is observed for E^*/A≥1.0 MeV/nucleon.