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 > 1014 eV) collected by the California HIgh school Cosmic ray ObServatory (CHICOS) array. Data from 60 detector sites spread over an area of 400 km2 were studied for evidence of isolated events separated by more than 1 km with coincidence times ranging from 1 µs up to 1 s. The results are consistent with the absence of excess coincidences except for a 2.9σ excess observed for coincidence times less than 10 µs. We report upper limits for the coincidence probability as a function of coincidence time.