Search for Correlated High Energy Cosmic Ray Events with CHICOS
  We present the results of a search for time correlations in high energy cosmic ray data (primary E > 10^{14} eV) collected by the California HIgh school Cosmic ray ObServatory (CHICOS) array. Data from 60 detector sites spread over an area of 400 km^2 were studied for evidence of correlated events separated by more than 1 km with coincidence times ranging from 1 microsec up to 1 second. All searches were consistent with the absence of excess coincidences except for a 2.9 sigma excess observed for coincidence times less than 10 microsec. We report upper limits for the coincidence probability as a function of coincidence time. 
B. E. Carlson, E. Brobeck, C. J. Jillings, M. B. Larson, T. W. Lynn,   R. D. McKeown, James E. Hill, B. Falkowski, R. Seki, ...