Mass of the rho^0 meson in ultra-relativistic heavy-ion collision
  We study the behavior of the rho vector mass in the context of the almost baryon-free environment of an ultra-relativistic heavy-ion collision. We show that rho scattering within the hadronic phase of the collision leads to a temperature dependent, decrease of its intrinsic mass at rest, compared to the value in vacuum. The main contributions arise from s-channel scattering with pions through the formation of a1 resonances as well as with nucleons through the formation of even parity, spin 3/2 [N(1720)] and 5/2 [Delta(1905)] nucleon resonances. We show that it is possible to achieve a shift in the intrinsic rho^0 mass of order - 40 MeV, when including the contributions of all the relevant mesons and baryons that take part in the scattering, for temperatures between chemical and kinetic freeze-out. 
Alejandro Ayala (ICN-UNAM), Jesus Guillermo Contreras   (CINVESTAV-Merida), J. Magnin (CBPF)