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First observation of a 'neutral current' event. In this photo from the Gargamelle bubble chamber at CERN, a beam of neutrinos enters from bottom. Being neutral, the neutrinos leave no tracks, but at bottom left one sets in motion an electron, which heads up the picture, curling & fragmenting as it radiates photons. This neutrino-electron interaction can only be a 'neutral current' event, due to the weak nuclear force & exchange of a force-carrying neutral Z particle. In 1972-3, Gargamelle physicists found this & 165 other examples of this interaction, which was predicted by the 'electroweak' theory.
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