SNO

          The Sudbury Neutrino Observatory, or SNO for short, is a spherical heavy water cherenkov detector located in the INCO's Creighton mine near Sudbury Ontario. The detector is composed of a 12 meter wide acrylic sphere, which contains roughly 1000 tonnes of heavy water and is housed in a 30 meter barrel filled with regular water. It is an example of the focused type of cherenkov detector, using an array of 9600 PMT's, surrounding the inner sphere, to record event patterns, energy and angular distribution. The detector chamber is near the bottom of the mine, at a depth of 2073 m, affording it a large amount of shielding from the surrounding rock which helps reduce the cosmic-ray background that is detected.

Left: Diagram of SNO
    detector.
Right: Taken using
    fisheye lense before
    final bottom PMT
    panel
    was installed.

The use of heavy water, which contains ²H instead of ¹H, allows the detector to detect all three flavours of neutrinos , electron neutrinos n_e, muon neutrino n_m, and tau neutrinos n_t. The three types of interactions which are used to produce the cherenkov radiation and so detect the neutrinos are:

#1. Charged Current Reaction:

         In charged current reactions, when an electron neutrino approaches the nucleus of a deuterium atom, the neutrino interacts by the weak force, being mediated by a W boson. This changes the neutron in the nucleus into a proton and as a result of conservation of charge the neutrino is changed to an electron. The electron receiving most of the neutrino's energy and is ejected at speeds close to c, resulting in the cherenkov effect.

#2. Neutral Current Reaction:

         In neutral current reactions the neutrino again interacts with the deuterium nucleus via the weak force. However, unlike charged current reactions the mediating particle is a Z boson, which is neutrally charged. This interaction breaks the nucleus apart. After it has thermalized, the resulting lone neutron goes through radiative capture with another nucleus releasing a gamma-ray. The gamma-ray then undergoes Compton scattering with electrons with cause cherenkov radiation. This reaction is equally responsive to all three neutrino types.

#3. Electron Scattering:

         In the electron scattering reaction, which is not specific to heavy water (and is the primary method for other similar detectors), a neutrino collides with an electron scattering it. This process is dominated, by a factor of six, by the electron neutrinos. As a result of the ratio of energy sharing between neutrino and electron there is a very small amount of spectral information, however very good directional information.

         One of the main focuses of research at SNO is studying the Solar Neutrino Problem (SNP) by studying the flux of electron neutrinos verses the total flux of neutrinos in the detector. Again the use of heavy water gives SNO this capability, which can be used to determine if neutrino oscillation, form electron neutrinos to one of the other flavours, is the solution to the SNP. In addition to heavy water, SNO has also used salt (NaCl) to enhance the neutron capture effeciency.

For a more detailed description of the Sudbury Neurtrino Observatory please see the website by Andrea Hughes. Or the official site Sudbury Neutrino Observatory.

Super Kamiokande

         The Super Kamiokande is a large water cherenkov detector similar to SNO. The detector is located at the Mozumi mine, 200 km north of Tokyo Japan, at a depth of 1000 m. The detector is a large cylindrical chamber 41.4 meter tall and 39.3 meters wide containing 32,000 tonnes of pure water in the inner volume and 18,000 tonnes of pure water in the outer volume. The purpose of the outer detector is to exclude cosmic ray muons, additionally, it is also used as a buffer to keep radiation emitted from the surrounding rock and walls from entering the inner detector volume. The inner detector is surrounded with 11,200 PMT's to detect the cherenkov radiation.
         Super Kamiokande is a focused cherenkov ring detector. Through measurements of the direction and intensity of the cherenkov radiation, information about interactions such as neutrino interactions or proton decay can be determined.

         The interactions of neutrinos in the detector are limited to the electron scattering reaction explained above with SNO:

Without heavy water it is not open to the other reactions.

          Some of the uses of Super Kamiokande include research into the Grand Unified Theories by searching for proton decay, and nucleon decay in general, and monopoles. Super Kamiokande is also used for observing solar, atmospheric and super nova neutrinos, studying the Solar Neutrino Problem (SNP) and cosmic rays, mainly muons made by cosmic rays in the atmosphere and in Earth. In addition, the detector is used to study dark matter through neutrino research.

Top: Artists sketch of the Super
 Kamiokande detector facility.
Bottom left: picture of the detector
 chamber before filled with water from 
 the detector bottom.
Bottom right: picture of technicians
 working on PMT's after the detector
 was partially filled with water.

For more detailed information see one of the official web sites, Super-Kamiokande U.S. Collaboration Home Page , or Super-Kamiokande Official Home Page .