From dileptons in heavy-ion collisions to chiral restoration at high temperature

Hadronic many-body theory predicts a strong broadening of the rho-meson spectral
function in hot and dense matter, leading to a melting of its resonance structure
as the pseudo-critical temperature is approached from below. Pertinent calculations
of thermal dilepton spectra in heavy-ion collisions, which additionally include
radiation from the quark-gluon plasma phase, are largely consistent with experimental
measurements which now cover a rather large range of collision energies, from SPS to
RHIC. The main part of this talk is devoted to analyzing the implications of this
scenario for the long-standing question of chiral symmetry restoration. Toward this
end, a combination of QCD and chiral Weinberg sum rules is utilized with inputs from
lattice-QCD for in-medium condensates and order parameters. Rather stringent
constraints on the a1(1260) spectral function - the chiral partner of the rho - are
deduced. Solutions are found which satisfy the temperature-dependent sum rules
accurately, thus suggesting that the rho melting scenario is compatible with chiral

Event Date: 
Tuesday, March 18, 2014 - 3:30pm
Event Location: 
Physics 298
Event Contact: 
Paul, Cristin
Event Contact Email: 
Event Contact Phone: 
Event Speaker: 
Ralf Rapp (Texas A&M)