Search for Neutral Q-balls in Super-Kamiokande II
  A search for Q-balls induced groups of successive contained events has been carried out in Super-Kamiokande II with 541.7 days of live time.   Neutral Q-balls would emit pions when colliding with nuclei, generating a signal of successive contained pion events along a track. No candidate for successive contained event groups has been found in Super-Kamiokande II, so upper limits on the possible flux of such Q-balls have been obtained. 
The Super-Kamiokande Collaboration: Y. Takenaga, et al