Exotic Θ+ baryon production induced by a photon and a pion -: art. no. 014009

We investigate the photoproduction of the Theta(+)(1540) on a nucleon (gamman-->K(-)Theta(+), gammap-->(K) over bar (0)Theta(+)) and the pion-induced Theta(+) production reaction on the proton (pi(-)p-->K(-)Theta(+)). The total cross sections near threshold are estimated by using hadronic models with effective interaction Lagrangians and form factors that preserve the gauge invariance of the electromagnetic current. The photoproduction cross sections are found to be a few hundred nb, with the cross section on the proton being larger than that on the neutron. The pion-induced production cross section is found to be around a few hundred mub but sensitive to the K*NTheta coupling whose value is not yet known. We also study the production cross section assuming that Theta(+) has negative parity. The cross sections are then found to be very suppressed compared to the case where Theta(+) has positive parity. Hence, the interpretation of the Theta(+) as an odd-parity pentaquark state seems to be disfavored from the estimates of the cross section for the photon-proton reaction from the SAPHIR experiment.