PION AND NEUTRON-PRODUCTION BY COSMIC-RAY MUONS UNDERGROUND

The production of positive pions and neutrons by cosmic muons at under ground sites of various depths is investigated. We first test the equi valent photon method in the particular case of Delta excitation by the muon. We find that this method, when it neglects the momentum depende nce of the transverse response, reproduces remarkably well the theoret ical muon cross section. This success has lead us to apply the method to higher energies, where it has not been tested. We evaluate in this way the production of positive pions in liquid scintillator from known photo-absorption cross sections. At a shallow depth of 20 meters our estimate reproduces the measurement. As for the neutron emission, we i nclude the obvious sources, such as the giant-resonance excitation, th e quasideuteron process, the quasifree pion production as well as neut rons emitted following pion capture. Our evaluation underestimates the number of neutrons produced and finds a too weak dependence on the de pth. This suggests that secondary neutron production is important at a ll depths.