Investigation of the reaction pp → pK0π+Λ in search of the pentaquark

The reaction pp → pK0π+Λ has been studied with the ANKE spectrometer at COSY-Julich at a beam momentum of 3.65 GeV/c in order to search for a possible signal of the pentaquark Θ+(1540), decaying into the pK0 system. By detecting four charged particles in the final state (π+, π− and two protons), the K0 and the Λ have been reconstructed to tag strangeness production. It has been found that the π+Λ missing-mass spectrum displays no significant signal expected from the Θ+(1540) excitation. The total cross section for the reaction pp → pK0π+Λ has been deduced, as well as an upper limit for the Θ+ production cross section. The intermediate Δ++K0Λ state seems to provide a significant contribution to the reaction.