Pi+ Pi- Emission in High-Energy Nuclear Collisions

Abstract

Realistic vacuum $\pi \pi$ interactions are employed to investigate thermal ${\pi }^{+}{\pi }^{-}$ emission spectra from the late stages of heavy-ion reactions at ultrarelativistic energies. Hadronic in-medium effects, including many-body $\rho$-meson spectral functions used earlier to describe the dilepton excess observed at CERN-SPS energies, are implemented to assess resulting modifications in relation to recent measurements of ${\pi }^{+}{\pi }^{-}$ invariant-mass spectra by the STAR collaboration in $p$-$p$ and $Au$-$Au$ collisions at $\sqrt{s_{NN}}$=200 GeV. Statistical model estimates for the ${\rho }^0/{\pi }^{-}$ and $K^{\ast }/K$ ratios close to the expected thermal freezeout are also given.

Comments: 9 pages RevTeX including 5 eps-figures, summary slightly expanded and 5 references added