Title: Dileptons and chiral symmetry restoration

Speaker: Paul Hohler (TAMU)

Abstract: A long standing goal in heavy ion physics is to identify an experimental signal for chiral symmetry restoration. Ideally this can be achieved by comparing the in-medium spectral functions of chiral partners, such as the light vector and axial-vector mesons (rho and a1). While the in-medium rho spectral function can be obtained from interpretations of dilepton data in heavy ion collisions, measuring the in-medium a1 spectral function remains elusive. This talk will thus discuss theoretical techniques which can be used to calculate the in-medium axial-vector spectral function given a rho spectral function which describes available dilepton data so that the question of chiral symmetry can be critically addressed. We will demonstrate that the combination of QCD and Weinberg sum rules provide a powerful selection method for the axial-vector spectral functions. Using this at different temperatures, we can obtain a temperature progression from the vacuum towards restoration, and show that experimental results of the vector channel suggest compatibility with restoration.  Results will also be presented from an effective theory approach which can calculate the spectral functions in both channels in vacuum and in-medium from a microscopic perspective. This serves as a foundation for future systematic studies in this area.