Observation of massive ΛKs0π+π+π−− events above 5

In an experiment using the Fermilab Multiparticle Spectrometer we have studied forward production of high mass events containing two strange particles and charged pions. In the final state ΛK s 0 π + π + π − π − we observe 5 events with effective mass above 5.5 GeV/ c 2 . Four of these events cluster near 5.75 GeV/ c 2 , and three of these events contain K s 0 π + π − mass combinations consistent with the charmed D 0 .