Search for diffuse cosmic gamma rays above 200 TeV

Abstract

A search has been made for gamma-rays in the cosmic radiation above 200 TeV using a two-level array of scintillators. Surface counters measure the size and direction of extensive airshowers while counters buried 3 m below the ground are used to measure their muon content in detail. No evidence for an excess number of muon-poor showers and conclude that gamma-rays comprise less than 0.4 percent of all cosmic rays above 200 TeV and less than 0.05 percent above 1000 TeV. The muon content of showers from the direction of the Galactic disk is the same as that of showers from other regions of the sky. The ratio of the flux of Galactic gamma-rays to that of cosmic rays is less than 8.0 x 10 to the -5th. This limit, based on muon measurements, represents a significant improvement over previous experiments and approaches predicted levels for diffuser gamma-rays from the Galactic plane.