New Result on Θ+ from LEPS

Abstract

We report new results of the Θ+ search by the LEPS collaboration. First, we applied exactly the same inclusive analysis as previous one to new data, where the proton and neutron contributions were not separated. The inclusive analysis does not show a strong narrow peak which was observed in the previous analysis. Thus, two results are inconsistent. In order to investigate the reason for the inconsistency, we have carried out a new analysis, where the proton contributions are identified by using the energy loss information of a trigger plastic scintillator called Start Counter. When proton events were selected, a peak structure was seen in the previous data. This indicates that a part of the peak structure in the previous data comes from statistical fluctuation. Furthermore, a clear signal enhancement was observed in the proton rejected sample. This enhancement was confirmed by subtracting the proton contribution estimated by a Monte-Carlo based simulation.