H. Sorge et al., PSI' PSI RATIO IN NUCLEUS-NUCLEUS COLLISIONS - A MEASURE FOR THE CHIRAL-SYMMETRY RESTORATION TEMPERATURE/, Physical review letters, 79(15), 1997, pp. 2775-2778
We argue that a decrease of the chiral scalar meson mass is responsibl
e for recreation of Psi' from J/Psi in ultrarelativistic nucleus-nucle
us collisions. This causes the charmonium yields to freeze out at temp
eratures close to the chiral symmetry restoration temperature T-c. As
a result the ratio Psi'/Psi may serve as a thermometer for T-c itself.
Results in a detailed reaction model support the conjecture. They sho
w good agreement with recent data of NA38 and NA50 for J/Psi and Psi'
production in S on U and Pb on Pb collisions.