Gargamelle

Found in July 1973, neutral currents were the first experimental indication of the existence of the Z0 boson, and consequently a major step towards the verification of the electroweak theory.

[1] In a series of separate works in the 1960s Sheldon Glashow, Steven Weinberg, and Abdus Salam came up with a theory that unified electromagnetic and weak interaction between elementary particles—the electroweak theory—for which they shared the 1979 Nobel Prize in Physics.

A charged particle travelling through the chamber will leave an ionization track, around which the liquid vaporizes, forming microscopic bubbles.

The entire chamber is subject to a constant magnetic field, causing the tracks of the charged particles to curve.

André Lagarrigue, an esteemed physicist at the École Polytechnique in Paris, and some of his colleagues, wrote the first published report, dated 10 February 1964, proposing the construction of a heavy liquid chamber to be built under the supervision of CERN.

[5] The final contract was signed on 2 December 1965, making this the first time in CERN's history that an investment of this kind was not approved by the council, but by the Director General using his executive authority.

Though the construction was delayed by about two years, it was finally assembled at CERN in December 1970, and the first important run occurred in March 1971.

To bend the tracks of charged particles, Gargamelle was surrounded by a magnet providing a 2 Tesla field.

The light source consisted of 21 point flashes disposed at the ends of the chamber body and over one half of the cylinder.

[8] The target material was chosen so that the hadrons produced in the collision was mainly pions and kaons, which both decay to neutrinos.

The produced pions and kaons have a variety of angles and energies, and consequently their decay product will also have huge momentum spread.

Instead, one focuses the secondary particles by using a magnetic horn, invented by Nobel laurate Simon van der Meer.

[8] During the years 1971-1976 large improvements factors were obtained in the intensity, first with a new injector for the PS — the Proton Synchrotron Booster — and secondly by the careful study of beam optics.

The first main quest of Gargamelle was to search for evidence of hard-scattering of muon-neutrinos and antineutrinos off nucleons.

The priorities changed in March 1972, when the first hints of the existence of hadronic neutral current became obvious.

The hadronic events have larger backgrounds, most extensively due to neutrons produced when neutrinos interact in the material around the chamber.

Firstly the neutrino and antineutrino cross-sections were shown to be linear with energy, which is what one expects for the scattering of point-like constituents in the nucleon.

Combining the neutrino and antineutrino structure functions allowed the net number of quarks in the nucleon to be determined, and this was in good agreement with 3.

View of Gargamelle bubble chamber detector in the West Hall at CERN , February 1977
The chamber of Gargamelle is currently on exhibition at CERN
An event in which the electron and neutrino changes momentum and/or energy by exchange of the neutral Z 0 boson . Flavors are unaffected.
Installation of the Gargamelle chamber body. Placement of the chamber in the oblong shaped magnet coils.
The inside of the bubble chamber. The fish-eye lenses can be seen on the walls of the chamber.
A schematic of the beam line between PS and Gargamelle bubble chamber
The magnetic horn of Simon van der Meer used in the neutrino beam line to Gargamelle.
This event shows the real tracks produced in the Gargamelle bubble chamber that provided the first confirmation of a leptonic neutral current interaction . A neutrino interacts with an electron , the track of which is seen horizontally, and emerges as a neutrino without producing a muon .