Search for Pentaquark States at CLAS

After the initial claim of discovery of a possible pentaquark state named Θ+(1540), many experiments reported positive and negative results opening a discussion about the existence of such exotic particle. Most of the experimental evidence was obtained from data previously collected for other purposes in many reaction channels and under very different kinematic conditions, so that direct comparison of the results of the different experiments are very difficult. New experiments with high resolution and high statistics are needed to solve the controversy. A comprehensive program to search for pentaquark in photoproduction reaction on proton and deuteron was undertaken at Jefferson Laboratory. These second generation experiments cover the few GeV region where most of the positive evidences were found, collecting more than 10 times the existing statistics. First experiments on proton and deuteron were completed showing no evidence for the Θ+(1540) and setting upper limits on the production cross section at the level of few nb.