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Pentaquark $Θ^+$ production from the reaction $γp\toπ^+K^-Θ^+$

The cross section for $Θ^+$ production from the reaction $γp\toπ^+K^-Θ^+$, which was observed in the CLAS experiment at the Jefferson National Laboratory, is evaluated in a hadronic model that includes couplings of $Θ^+$ to both $KN$ and $K^*N$. With their coupling constants determined from the empirical $πNN(1710)$ and $ρNN(1710)$ coupling constants using the SU(3) symmetry, the cross section for this reaction has been evaluated by taking $Θ^+$ to have spin 1/2 and isospin 0 but either positive or negative parity. We find that the cross section is 10-15 nb if $Θ^+$ has positive parity as predicted by the chiral soliton model. The cross section is reduced by more than a factor of 10 if $Θ^+$ has negative parity as given by lattice QCD studies. For both parities, the differential distribution peaks at small negative four momentum transfer as expected from the dominating $t$-channel kaon-exchange diagram that involves only the coupling of $Θ^+$ to $KN$.