Delta(1232) and Nucleon Spectral Functions in Hot Hadronic Matter

Hendrik van Hees, Ralf Rapp

Published 2004-07-16, updated 2004-10-25Version 2

Modifications of Delta(1232) and nucleon spectral functions at finite temperature and baryon density are evaluated in terms of resonant scattering off thermal pions, as well as a renormalization of the vacuum Delta-width including vertex corrections. The interactions are based on effective Lagrangians of pions and baryon resonances, with underlying parameters (coupling constants and form factors) determined by the elastic pi N scattering phase shift in the isobar channel, and by empirical decay branchings of excited resonances. Pion modifications are included via interactions in a pion gas, as well as standard Delta- and nucleon-hole excitations in nuclear matter. In hot hadronic matter, under conditions resembling thermal freezeout at the Relativistic Heavy-Ion Collider (RHIC), the Delta exhibits a significant broadening of ~65 MeV together with a slight upward peak shift of 5-10 MeV, in qualitative agreement with preliminary data from the STAR collaboration.