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Identifying photons and electrons in cosmic rays

As part of the Large Array experiments we commissioned a detector of Pb glass (like Waterford crystal) to identify the electron and photon components in cosmic rays at the Earth’s surface. The Pb-glass does not scintillate, but it is sensitive to Cerenkov radiation given off by particles traveling faster than the speed of light in glass. This is the light equivalent of a sonic boom where sound waves build up because an object is moving faster than sound in the air. The Pb-glass was loaned to us from an experiment at Fermilab that measured proton-anitproton annihilations.