Gargamelle

Gargamelle was a bubble chamber at CERN designed to detect neutrinos

Gargamelle was a bubble chamber at CERN designed to detect neutrinos. It operated from 1970 to 1976 with a muon-neutrino beam produced by the CERN Proton Synchrotron, before moving to the Super Proton Synchrotron (SPS) until 1979.

Gargamelle was 4.8 metres long and 2 metres in diameter. It weighed 1000 tonnes and held nearly 12 cubic metres of heavy-liquid freon (CF3Br).

As neutrinos have no charge, they do not leave tracks in detectors. The freon in the Gargamelle detector revealed any charged particles set in motion by the neutrinos and so revealed the interactions indirectly. Using freon instead of the more typical liquid hydrogen increased the probability of seeing neutrino interactions.

Early results from Gargamelle, in the period 1972-4, provided crucial evidence for the existence of quarks, the fundamental constituents of particles such as protons and neutrons. Combining the neutrino results with those from experiments using an electron beam at SLAC in the US showed that the quarks must have charges that are 1/3 or 2/3 the charge of the proton, just as predicted.

In July 1973, in a seminar at CERN, the Gargamelle collaboration presented the first direct evidence of the weak neutral current - a process predicted in the mid-1960s independently by Sheldon Glashow, Abdus Salam and Steven Weinberg - that required the existence of a neutral particle to carry the weak fundamental force. This particle, called the Z boson, and the associated weak neutral currents, were predicted by electroweak theory, according to which the weak force and the electromagnetic force are different versions of the same force.

The discovery involved the search from two types of events: one involving the interaction of a neutrino with an electron in the liquid; in the other the neutrino scattered from a hadron (proton or neutron). The signature of a neutral current event was an isolated vertex from which only hadrons were produced. By July 1973 they had confirmed as many as 166 hadronic events, and one electron event. In both cases, the neutrino enters invisibly, interacts and then moves on, again invisibly. On 3 September the collaboration published two papers on these events in the same issue of Physics Letters.

In 1983, two CERN experiments, UA1 and UA2, discovered the W and Z particles, carriers of the electroweak force.

In its short career at the SPS, Gargamelle succeeded in observing for the first time a touchstone weak interaction, involving only leptons, in which a muon-type neutrino hits an electron, producing an electron-neutrino and a muon. However in 1969 the chamber ceased operation after cracks had appeared that proved impossible to repair. The chamber body went on to be a main feature in CERN's Microcosm garden.

The name of the chamber derives from the giantess Gargamelle in the works of François Rabelais; she was Gargantua's mother.

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