Thermodynamics of Δ resonances

The thermodynamic potential of a system of pions and nucleons is computed including the pi N interactions in the P-33 channel. A consistent treatment of the width of the resonance in this channel, the Delta(1232) resonance, is explored in detail. Ln the low-density limit we recover the leading term of the virial expansion for the thermodynamic potential. An instructive diagrammatic interpretation of the contributions to the total baryon number is presented. Furthermore, we examine within a fireball model the consequences for the pion spectra in heavy-ion collisions at intermediate energies, including the effect of collective flow. A consistent treatment of the Delta width leads to a substantial enhancement of the pion yield at low momenta. (C) 1998 Elsevier Science B.V. All rights reserved.