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38-476: Gargamelle is famous for being the experiment where neutral currents were discovered. Found in July 1973, neutral currents were the first experimental indication of the existence of the Z boson , and consequently a major step towards the verification of the electroweak theory . Gargamelle can refer to both the bubble chamber detector itself, or the high-energy physics experiment by the same name. The name itself

76-453: A collaboration consisting of seven laboratories: École Polytechnique Paris , RWTH Aachen , ULB Bruxelles , Istituto di Fisica dell'Università di Milano , LAL Orsay , University College London and CERN. The group met in Milan in 1968 to list the physics priorities for the experiment: today Gargamelle is famous for its discovery of the neutral currents, but while preparing the physics program

114-470: A neutrino and an antineutrino beam. The invention of van der Meer increased the neutrino flux by a factor of 20. The neutrino beam had an energy between 1 and 10 GeV. After being focused, the pions and kaons were directed through a 70 m long tunnel, allowing them to decay. Pions and kaons that did not decay hit a shielding in the end of the tunnel and were absorbed. When decaying, pions and kaons normally decay in π → μ + ν and K → μ + ν , meaning that

152-582: A neutrino scattered from a hadron, e.g. ν + p → ν + p , ν + n → ν + p + π or p → ν + n + π , plus events with many hadrons. The leptonic events have small cross-sections , but correspondingly small background. The hadronic events have larger backgrounds, most extensively due to neutrons produced when neutrinos interact in

190-644: A pillar of the Standard Model . The final experimental proof the electroweak theory came in 1983, when the UA1 and UA2 collaboration discovered the W and Z bosons . Initially the first priority of the Gargamelle had been to measure the neutrino and antineutrino cross-sections and structure functions . The reason for this was to test the quark model of the nucleon. Firstly the neutrino and antineutrino cross-sections were shown to be linear with energy, which

228-502: Is where the neutral currents describing the flow of the neutrino and of the electron are given by: where: and   g A f = T 3 ( f )   {\displaystyle \ g_{\mathsf {A}}^{f}=T_{3}(f)\ } are the vector and axial couplings for fermion   f   . {\displaystyle \ f~.}   T 3   {\displaystyle \ T_{3}\ } denotes

266-421: Is derived from a 16th-century novel by François Rabelais , The Life of Gargantua and of Pantagruel , in which the giantess Gargamelle is the mother of Gargantua. 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

304-471: Is determined by a derived quantum number called weak charge , which acts similarly to weak isospin for interactions with the W ;bosons. The neutral current that gives the interaction its name is that of the interacting particles. For example, the neutral current contribution to the ν e e → ν e e elastic scattering amplitude

342-507: Is no transfer of electric charge, the exchange of a Z is referred to as " neutral current ". Neutral currents were a prediction of the electroweak theory. In 1960 Melvin Schwartz proposed a method of producing an energetic neutrino beam . Such a beam was then used by Schwartz and others in an experiment in 1962 at Brookhaven which showed that there are different types of neutrinos: muon neutrinos and electron neutrinos . Schwartz shared

380-506: 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. In addition comparing the neutrino results with results from Stanford Linear Accelerator Center (SLAC) in the US, using an electron beam, one found that quarks had fractional charges, and experimentally proved

418-669: The Sudbury Neutrino Observatory experiment. Weak neutral currents were predicted by electroweak theory developed mainly by Abdus Salam , John Clive Ward , Sheldon Glashow and Steven Weinberg , and confirmed shortly thereafter in 1973, in a neutrino experiment in the Gargamelle bubble chamber at CERN . RWTH Aachen Too Many Requests If you report this error to the Wikimedia System Administrators, please include

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456-530: The weak isospin of the fermions, Q their electric charge and   Q W   {\displaystyle \ Q_{\mathsf {W}}\ } their weak charge . These couplings amount to essentially left chiral for neutrinos and axial for charged leptons . The Z boson can couple to any Standard Model particle, except gluons and photons ( sterile neutrinos would also be an exception, if they were found to exist). However, any interaction between two charged particles that can occur via

494-474: The 1979 Nobel Prize in Physics . Their theory predicted the existence of the W and Z bosons as propagators of the weak force . W bosons have electric charge, either positive (W) or negative (W), the Z, however, has no charge. Exchange of a Z boson transfers momentum , spin , and energy but leaves the particle's quantum numbers unaffected—charge, flavor , baryon number , lepton number , etc. Since there

532-407: The 1988 Nobel Prize in Physics for this discovery. Prior to Schwartz' idea weak interactions had been studied only in the decay of elementary particles, especially strange particles . Using these new neutrino beams greatly increased the energy available for the study of the weak interaction. Gargamelle was one of the first experiments that made use of a neutrino beam, produced with a proton beam from

570-412: The Gargamelle collaboration presented the discovery of neutral currents at a seminar at CERN. The Gargamelle collaboration discovered both leptonic neutral currents — events involving the interaction of a neutrino with an electron — and hadronic neutral currents — events when a neutrino is scattered from a nucleon. The discovery was very important as it was in support of the electroweak theory , today

608-451: The PS. A bubble chamber is simply a container filled with a superheated liquid. 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. The radius of curvature is proportional to the momentum of

646-565: The amplitude of the electromagnetic process. Particle accelerators with energies necessary to observe neutral current interactions and to measure the mass of Z boson weren't available until 1983. On the other hand, Z boson interactions involving neutrinos have distinctive signatures: They provide the only known mechanism for elastic scattering of neutrinos in matter; neutrinos are almost as likely to scatter elastically (via Z boson exchange) as inelastically (via W boson exchange), of major experimental significance, in, e.g. ,

684-433: The chamber was illuminated and photographed. The illumination system emitted light that was scattered at 90° by the bubbles, and sent to the optics. The light source consisted of 21 point flashes disposed at the ends of the chamber body and over one half of the cylinder. The optics were situated in the opposite half of the cylinder, distributed in two rows parallel to the chamber axis, each rows having four optics. The objective

722-457: The constituents of matter. Neutrinos have extremely small cross sections , i.e., the probability of interaction is very small. Whereas bubble chambers typically are filled with liquid hydrogen , Gargamelle was filled with a heavy liquid— CBrF 3 (Freon)—increasing the probability of seeing neutrino interactions. The domain of neutrino physics was in rapid expansion in the 60's. Neutrino experiments using bubble chambers were already running at

760-583: The council, but by the Director General using his executive authority. The Gargamelle chamber was entirely constructed at Saclay . 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. Gargamelle was 4.8 meters long and 2 meters in diameter, and held 12 cubic meters of heavy liquid Freon. To bend

798-482: The exchange of a virtual Z boson can also occur via the exchange of a virtual photon . Unless the interacting particles have energies on the order of the Z ;boson mass (91 GeV) or higher, the virtual Z boson exchange has an effect of a tiny correction,   ( E / M Z ) 2   , {\displaystyle \ (E/M_{\mathrm {Z} })^{2}\ ,} to

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836-462: The first synchrotron at CERN, the PS, and the question of the next generation of bubble chambers had been on the agenda for some time. 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. He formed

874-441: The flux of neutrinos would be proportional to the flux of muons. As the muons were not absorbed as hadrons, the flux of charged muons was stopped by an electromagnetic slowing down process in the long shielding. The neutrino flux was measured through the corresponding muon flux by means of six planes of silicium-gold detectors placed at various depths in shielding. During the years 1971-1976 large improvements factors were obtained in

912-479: 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. It

950-438: The interacting particles' quantum numbers unaffected – charge, flavor , baryon number , lepton number , etc. Because there is no transfer of electrical charge involved, exchange of Z particles is referred to as "neutral" in the phrase "neutral current". However the word "current" here has nothing to do with electricity – it simply refers to the exchange of the Z particle. The Z boson's neutral current interaction

988-475: The material around the chamber. Neutrons, being of no charge, would not be detected in the bubble chamber, and the detection of their interactions would mimic neutral currents events. In order to reduce the neutron background, the energy of the hadronic events had to be greater than 1 GeV. The first example of a leptonic event was found in December 1972 at Gargamelle by a graduate student from Aachen . By March 1973 166 hadronic events had been found, 102 events with

1026-480: The most well known of the exchange particles for the weak force is the W ;particle which is involved in beta decay . W particles have electric charge – there are both positive and negative W particles – however the Z boson is also an exchange particle for the weak force but does not have any electrical charge. Exchange of a Z boson transfers momentum , spin , and energy , but leaves

1064-570: The necessary degrees of freedom in position and orientation for adjusting the beam onto target. The target was a cylinder of beryllium , 90 cm long and 5 mm in diameter. 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. As neutrinos have no charge, they cannot be focused with electric or magnetic fields. Instead, one focuses

1102-400: The neutrino beam and 64 events with the antineutrino beam. However, the question of neutron background hung over the interpretation of the hadronic events. The problem was solved by studying the charged current events which also had an associated neutron interaction which satisfied the hadronic event selection. In this way one has a monitor of the neutron background flux. On the 19th of July 1973

1140-404: The particle. The tracks are photographed, and by studying the tracks one can learn about the properties of the particles detected. The neutrino beam which travelled through the Gargamelle bubble chamber did not leave any tracks in the detector, since neutrinos have no charge. Interactions with neutrinos were therefore detected, by observing particles produced by the interactions of the neutrinos with

1178-447: The secondary particles by using a magnetic horn , invented by Nobel laurate Simon van der Meer . The shape of the horn and the strength of the magnetic field can be tuned to select a range of particles that are to be best focused, resulting in a focused neutrino beam with a chosen range of energy as the kaons and pions decay. By reversing the current through the horn, one could produce an antineutrino beam . Gargamelle ran alternately in

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1216-409: The topic was not even discussed, and in the final proposal it is ranked as fifth in priority. At the time there was no consensus around the electroweak theory, which might explain the list of priorities. Also, earlier experiments looking for neutral currents in the decay of the neutral kaon into two charged leptons , had measured very small limits of around 10. Due to budgetary crisis, the experiment

1254-427: The tracks of charged particles, Gargamelle was surrounded by a magnet providing a 2 Tesla field. The coils of the magnet were made of copper cooled down with water, and followed the oblong shape of Gargamelle. In order to maintain the liquid at an adequate temperature several water tubes surrounded the chamber body, to regulate the temperature. The entire installation weighed more than 1000 tons. When recording an event,

1292-479: The values of these charges: + 2 ⁄ 3   e , − 1 ⁄ 3  e. The results were published in 1975, providing crucial evidence for the existence of quarks. Neutral currents Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force . These interactions are mediated by the Z ;boson . The discovery of weak neutral currents

1330-414: Was a significant step toward the unification of electromagnetism and the weak force into the electroweak force , and led to the discovery of the W and Z bosons . The weak force is best known for its role in nuclear decay. It has very short range but (apart from gravity) is the only force to interact with neutrinos . Like other subatomic forces, the weak force is mediated via exchange particles. Perhaps

1368-413: Was made by an assembly of lenses with a 90° angular field followed by a divergent lens which extends the field to 110°. Gargamelle was designed for neutrino and antineutrino detection. The source of neutrinos and antineutrinos was a proton beam at an energy of 26 GeV from the PS. The protons were extracted by a magnet and then directed through an appropriate array of quadrupole and dipole magnets, providing

1406-459: Was not approved in 1966, contrary to what was expected. Victor Weisskopf , Director General at CERN , and Bernard Grégory , Scientific Director, decided to commit the money themselves, the latter offering a loan to CERN to cover the instalment due for 1966. 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

1444-487: Was then decided to make a two-prong attack in the search for neutral current candidates. One line would search for leptonic events — events involving the interaction with an electron in the liquid, e.g. ν μ + e → ν μ + e or ν μ + e → ν μ + e . The other line would search for hadronic events — involving

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