Dileptons Get Nearly "Blind" to Mass-Scaling Effects In Hot and/or Dense Matter

Mannque Rho

Published 2009-12-16, updated 2009-12-21Version 3

Based on BHHRS and further sharpened by discussions with Gerry Brown that I had in October 2008, we arrive at the present assessment of the dilepton saga, namely, that dileptons become "blind" to changes in the vacuum structure of chiral symmetry (such as, e.g., BR scaling at high temperature and/or at high density and hence are {\em not} an appropriate probe for a signal for partial or complete chiral restoration, contrary to what has been widely believed. There, however, are a variety of indirect indications that the scaling notion is qualitatively, if not quantitatively, valid and should work in various low-energy nuclear phenomena, and it is fair to conclude that while there is no direct evidence for the scaling notion, there is {\em none against} it either, in a strong disagreement with what was claimed in CERN Courier November 2009. I will touch briefly on certain observables that could give a clear-cut litmus signal for the vacuum structure of chiral symmetry modified by temperature and/or density.