Pentaquark U+ production from the reaction gp\p+K−U+

The cross section for U+ production from the reaction gp→p+K−U+, which was observed in the CLAS experiment at the Jefferson National Laboratory, is evaluated in a hadronic model that includes couplings of U+ to both KN and K*N. With their coupling constants determined from the empirical pNNs1710d and rNNs1710d coupling constants using the SU(3) symmetry, the cross section for this reaction has been evaluated by taking U+ to have spin 1/2 and isospin 0 but either positive or negative parity. We find that if U+ has positive parity as predicted by the chiral soliton model and the correlated quark model, the cross section is 50–110 nb, depending on the value of the K*NU coupling. The cross section is reduced by more than a factor of 10 if U+ has negative parity as given by lattice QCD studies and the uncorrelated quark model. For both parities, the differential cross section peaks at small negative four-momentum transfer when the reaction is dominated by the t-channel kaon-exchange diagram that involves only the coupling of U+ to KN. After decreasing with increasing negative four-momentum transfer, the differential cross section increases again when the u-channel contribution due to intermediate U+ propagation becomes important at large negative four-momentum transfer.