Chiral and UA(1) phase transitions in QCD: an analysis of the I=0 pseudoscalars

We study chiral and UA(1) phase transition in the dilute gas approximation. A comprehensive analysis of the mass and mixing angel of η and η′ reveals that in the transition of the quark-gluon-plasma droplets to the hadrons, besides the chiral phase transition, the UA(1) phase transition also plays a significant and non-trivial role.