Gamma ray astronomy: The particle physics connection

Abstract

A plethora of unexpected phenomena has been revealed by p p coliiders at center-of-mass energies of order 1 TeV. They are associated with jet production and could not have been anticipated from low energy data which exhibit approximate scaling behavior. We investigate whether the same underlying physics can be responsible for some puzzling features of γ-initiated air showers, most notably their seemingly large hadron (muon) content. We conclude that the average properties of high energy photon shower could be significantly modified, but we argue that individual γ-ray showers are not expected to impersonate hadron showers. The latter can therefore be discriminated against in a search for point sources and diffuse γ-rays, e.g., those produced by interaction of cosmic rays on the interstellar medium or on 3°K microwave photons. If, on the contrary, photons are indeed muon-rich, we argue that new physics has to be invoked and that underground experiments such as Dumand and Grande will be γ-ray as well as neutrino telescopes, competitive with the largest air shower arrays.