Neutrino

:Neutrino is also an operating system. See QNX.

Neutrino detection

Neutrinos can interact via the neutral currect (involving the exchange of a Z boson) or charged current (involving the exchange of a W boson) weak interactions.

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• In a neutral current interaction, the neutrino leaves the detector after having transfered some of its energy and momentum to a target particle. All three neutrino flavors can participate regardless of the neutrino energy. However, no neutrino flavor information is left behind.
• In a charged current interaction, the neutrino transforms into its partner lepton (electron, muon, or tau). However, if the neutrino does not have sufficient energy to create its heavier partner's mass, the charged current interaction is unavailable to it. Solar and reactor neutrinos have enough energy to create electrons. Most accelerator-based neutrino beams can also create muons, and a few can create taus. A detector which can distinguish among these leptons can reveal the flavor of the incident neutrino in a charged current interaction. Since the interaction involves the exchange of a charged boson, the target particle also changes character (e.g., neutron ? proton).

Antineutrinos were first detected in 1953 near a nuclear reactor. Reines and Cowan used two targets containing a solution of cadmium chloride in water. Two scintillation detectors were placed next to the cadmium targets. Antineutrino charged current interactions with the protons in the water produced positrons and neutrons. The resulting positron annihilations with electrons created photons with an energy of about 0.5 MeV. Pairs of photons in coincidence could be detected by the two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei resulting in gamma rays of about 8 MeV that were detected a few microseconds after the photons from a positron annihilation event.

Related Topics:
1953 - Reines - Cowan

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Chlorine detectors consist of a tank filled with carbon tetrachloride. A neutrino converts a chlorine atom into one of argon via the charged current interaction. The fluid is periodically purged with helium gas which would remove the argon. The helium is then cooled to separate out the argon. A chlorine detector in the former Homestake Mine near Lead, South Dakota, containing 520 short tons (470 metric tons) of fluid, made the first measurement of the deficit of electron neutrinos from the sun (see solar neutrino problem). A similar detector design uses a gallium ? germanium transformation which is sensitive to lower energy neutrinos. These chemical detection methods are useful only for counting neutrinos; no neutrino direction or energy information is available.

Related Topics:
Carbon tetrachloride - Chlorine - Argon - Helium - Homestake Mine - Lead, South Dakota - Short ton - Metric ton - Solar neutrino problem - Gallium - Germanium

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"Ring-imaging" detectors take advantage of the Cherenkov light produced by charged particles moving through a medium faster than the speed of light in that medium. In these detectors, a large volume of clear material (e.g., water) is surrounded by light-sensitive photomultiplier tubes. A charged lepton produced with sufficient energy creates Cherenkov light which leaves a characteristic ring-like pattern of activity on the array of photomultiplier tubes. This pattern can be used to infer direction, energy, and (sometimes) flavor information about the incident neutrino. Two water-filled detectors of this type (Kamiokande and IMB) recorded the neutrino burst from supernova 1987a. The largest such detector is the water-filled Super-Kamiokande.

Related Topics:
Cherenkov light - Photomultiplier - IMB - Supernova 1987a

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The Sudbury Neutrino Observatory (SNO) uses heavy water. In addition to the neutrino interactions available in a regular water detector, the deuterium in the heavy water can be broken up by a neutrino. The resulting free neutron is subsequently captured, releasing a burst of gamma rays which are detected. All three neutrino flavors participate equally in this dissociation reaction.

Related Topics:
Sudbury Neutrino Observatory - Heavy water

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The MiniBooNE detector employs pure mineral oil as its detection medium. Mineral oil is a natural scintillator, so charged particles without sufficient energy to produce Cherenkov light can still produce scintillation light. This allows low energy muons and protons, invisible in water, to be detected.

Related Topics:
MiniBooNE - Scintillator

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Tracking calorimeters such as the MINOS detectors (see the NuMI-MINOS project page) use alternating planes of absorber material and detector material. The absorber planes provide detector mass while the detector planes provide the tracking information. Steel is a popular absorber choice, being relatively dense and inexpensive and having the advantage that it can be magnetised. The No ua proposal suggests the use of particle board as a cheap way of getting a large amount of less dense mass. The active detector is often liquid or plastic scintillator, read out with photomultiplier tubes, although various kinds of ionisation chambers have also been used. Tracking calorimeters are only useful for high energy (GeV range) neutrinos. At these energies, neutral current interactions appear as a shower of hadronic debris and charged current interactions are identified by the presence of the charged lepton's track (possibly alongside some form of hadronic debris.) A muon produced in a charged current interaction leaves a long penetrating track and is easy to spot. The length of this muon track and its curvature in the magnetic field provide energy and charge (mu^+ versus mu^-) information. An electron in the detector produces an electromagnetic shower which can be distinguished from hadronic showers if the granularity of the active detector is small compared to the physical extent of the shower. Tau leptons decay essentially immediately to either pions or another charged lepton, and can't be observed directly in this kind of detector. (To directly observe taus, one typically looks for a kink in tracks in photographic emulsion.)

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Most neutrino experiments must address the flux of cosmic rays that bombard the earth's surface. The higher energy (>50 MeV or so) neutrino experiments often cover or surround the primary detector with a "veto" detector which reveals when a cosmic ray passes into the primary detector, allowing the corresponding activity in the primary detector to be ignored ("vetoed"). For lower energy experiments, the cosmic rays are not directly the problem. Instead, the spallation neutrons and radioisotopes produced by the cosmic rays may mimic the desired physics signals. For these experiments, the solution is to locate the detector deep underground so that the earth above can reduce the cosmic ray rate to tolerable levels.

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Some neutrino detectors are:

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• Antarctic Muon And Neutrino Detector Array
• Project DUMAND
• Super-Kamiokande
• LSND
• MiniBooNE