Eur. Phys. J. C (2007) 49: 219-224
https://doi.org/10.1140/epjc/s10052-006-0072-y

Regular Article – Theoretical Physics

What does the ρ-meson do? In-medium mass shift scenarios versus hadronic model calculations

¹ Department of Physics, McGill University, 3600 Rue University, Montréal, QC, Canada H3A 2T8,
² Department of Physics, Duke University, P.O. Box 90305, Durham, NC, 27708, USA
³ Department of Physics, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland
⁴ Helsinki Institut of Physics, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland

^* e-mail: ruppert@physics.mcgill.ca

Received: 3 August 2006
Published online: 26 October 2006

Abstract

The NA60 experiment has studied low-mass muon pair production in In–In collisions at 158 A GeV with unprecedented precision. With these results there is hope that the in-medium modifications of the vector meson spectral function can be constrained more thoroughly than before. We investigate in particular what can be learned about collisional broadening by a hot and dense medium and what constraints the experimental results put on in-medium mass shift scenarios. The data show a clear indication of considerable in-medium broadening effects but disfavor mass shift scenarios where the ρ-meson mass scales with the square root of the chiral condensate. Scaling scenarios which predict at finite density a dropping of the ρ-meson mass that is stronger than that of the quark condensate are clearly ruled out since they are also accompanied by a sharpening of the spectral function.