Δ Resonance Production in ⁵⁸Ni+Cu Collisions at E  =  1.97A GeV

Invariant mass analyses of (p,π^±) pairs in ⁵⁸Ni+Cu collisions at 1.97A GeV have been performed and show correlations resulting from the decays of the Δ resonance, the Λ baryon, and possibly the N^*(1440) resonance. A reduction in the Δ mass is observed and the mass reduction increases with collision centrality. Events generated by the relativistic cascade model (ARC) also reveal a mass reduction. The mass reduction is related to the size of the reaction volume and the details of Δ production mechanisms in heavy ion collisions.