Chiral symmetry and dileptons in heavy ion collisions

Abstract

Abstract.We study the consequences of chiral symmetry restoration for thermal production of dileptons in central nucleus-nucleus collisions. We discuss the temperature dependence of various hadronic parameters entering the dilepton cross-section, putting emphasis on universal properties in the vicinity of a 2nd order chiral symmetry restoring phase transition and the constraints on their temperature dependence known from lattice simulations. It is shown that the modifications of the hadron spectrum due to medium effects can lead to important changes of the thermal dilepton production rate in heavy ion collisions. In particular, it can imply the suppression of a thermal p peak.

Excess low energy photon pairs from pion annihilation at the chiral phase transition

“…Similar expressions can be found in [18] for dilepton production rates. Note that the cross section σ π + π − →γγ = σ π + π − →γγ (s = M 2 , T, µ) is medium dependent and obtained from (12).…”

Phi meson production in heavy-ion collisions at SIS energies

“…In this case, one can also study the phi meson in-medium properties via the dilepton spectrum from these collisions as pointed out in Refs. [4,13,14]. At high temperature, the reduction of phi meson mass may become more appreciable because of the decrease of strangeness condensate ss as a result of the presence of strange hadrons [5].…”

Physics at the relativistic heavy ion collider

“…At lower invariant masses between 0.5 and 1 GeV, lepton pairs from hadronic sources are expected to dominate and provide information on possible medium modifications of hadrons at high density [10,11]. The widths and positions of the p,w, and r peaks in the lepton pair invariant mass spectrum are expected to be sensitive to medium-induced changes of the hadronic mass spectrum, especially to a drop of vector meson masses preceding chiral symmetry restoration [12,13,14,15,16,17,18,19,20].…”