Discovery of neutral currents
Frederick W. Bullock · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1973
It is claimed that interactions which are examples of neutral current processes were observed at CERN. Such processes would link together the world of electromagnetic phenomena and that of the weak interactions. This crucial experiment exploited the observational difference between leptons and hadrons. High energy protons, extracted from the proton synchrotron, were allowed to impinge on a heavy metal target. The hadron beam produced, containing a large flux of pi and K-mesons passed through the drift space which was terminated by a monumental wall of several tons of iron and concrete. In this wall all the remaining hadrons and mesons were extracted leaving only neutrinos. These traversed a giant bubble chamber. On examining the interaction in the chamber photographically it was found that while the expected processes giving a charged muon were indeed taking place there was, neverttheless, a significant number of interactions where no charged muon appearced among the interaction products. The inference is that these muonless interactions are manifestations of the neutral current process where the lepton coming out of the interaction is a neutrino which cannot, of course, be detected. (UK)