Photoproduction of Pentaquark $\Theta^+$ and Chiral Symmetry Restoration   in Hot and Dense Medium
  The photoproduction rate of pentaquark $\Theta^+$ is calculated in a hot and dense medium. At high temperature and density, due to the restoration of chiral symmetry, photoproduction energy threshold is increased. Above the thresold the production cross section is strongly enhanced. 
Xuewen Hao and Pengfei Zhuang