Alternatives for understanding qualitative features that dominate particle-particle correlations in heavy-ion reactions of ∼50 MeV/nucleon

We use trajectory calculations to analyze small-angle particle-particle correlations for three typical situations: 40Ar+197Au (E/A=60 MeV)→2H-2H pairs and 1H-1H pairs, 20Ne+59Cu (E/A=30 MeV)→n-n pairs. For the 2H-2H pairs our analysis of the gentle featureless anticorrelations suggests that the major driving force is Coulomb repulsion after a range of average time delays from ∼5x10-21 s for the 2H pairs of lower energy to ∼10-22 s for the 2H pairs of higher energy. Simulations are used to illustrate the separate dominance of source size and lifetime in the space-time extent of the emitter. For lifetimes ≤10-22 s the emitter size dominates; for longer lifetimes the time delays become predominant. The peaks at ∼20 MeV/c in the correlation functions for 1H-1H pairs can be accounted for by diproton ejection which decays into protons with a Q value of ∼0.35 MeV and a decay width of ∼1 MeV (or a meanlife of 6x10-22 s). The positive correlations between neutron pairs can be accounted for by dineutron ejection which decays into neutrons with a near zero Q value and a decay width of ∼0.25 MeV (or a meanlife of ∼2x10-21 s). If these diproton and dineutron clusters do indeed have a metastable existence, then one should reexamine the notion that their associated small-angle correlations reflect the space-time extent of the emission source