Understanding pentaquark States in QCD.
We estimate the mass of the pentaquark state with QCD sum rules and find that pentaquark states with isospin I=0,1,2 lie close to each other around (1.55+/-0.15) GeV. The experimentally observed baryon resonance Theta(+)(1540) with S=+1 can be consistently identified as a pentaquark state if its J(P)=1 / 2(-). Such a state is expected in QCD. If its parity is positive, this pentaquark state is really exotic. The outstanding issue now is to determine its quantum numbers experimentally.
Zhu
Shi-Lin
SL
Department of Physics, Peking University, Beijing 100871, China.