Golden Jubilee photos: A gargantuan discovery

In July 1973, a groundbreaking discovery was announced in CERN's Main Auditorium: the Gargamelle group had found proof of the weak neutral current. The discovery confirmed the electroweak theory, which had predicted that the weak force and the electromagnetic force were different facets of the same interaction. This paved the way for the Grand Unified Theory, which holds that just after the birth of the Universe all forces were actually the same...
Gargamelle, whose "body" now reposes in the Microcosm garden, was a huge bubble chamber weighing around 1000 tonnes, filled with 18 tonnes of liquid freon. Its size, worthy of the giant Gargantua - the son of Gargamelle - was mighty enough to catch neutrinos, the elusive neutral particles which career through space without leaving any tracks. In the photograph, an unseen neutrino interacts with an electron and emerges as a neutrino instead of changing into a muon - what is seen (vertically) is the track of the electron. This lepton event offers proof of the existence of neutral currents.