Ground level muons in coincidence with the solar flare of April 15, 2001

The counting rate of single muon tracks from the Project GRAND proportional wire chamber array is examined during the Ground Level Event (GLE) of April 15, 2001. The GLE was seen by neutron monitor stations shortly after the time of the solar X-ray flare. GRAND's single muon data are presented and compared with neutron monitor data from Climax, Newark, and Oulu. The single muon data have mean primary hadron energies higher than those of these neutron monitor stations and so contain information about higher energy hadrons. For the single muon data for Project GRAND, the GLE is detected at a statistical significance of 6.1-sigma.