The world’s largest detector for high-energy neutrinos was completed December 18 2010, when scientists lowered the last of 5,160 sensors more than a mile beneath the ice of the Antarctic plateau.
The electron neutrino (a lepton) was first postulated in 1930 by Wolfgang Pauli to explain why the electrons in beta decay were not emitted with the full reaction energy of the nuclear transition. The apparent violation of conservation of energy and momentum was most easily avoided by postulating another particle. Enrico Fermi called the particle a neutrino and developed a theory of beta decay based on it, but it was not experimentally observed until 1956.
Wolfgang Pauli introduced the neutrino to the world of physics in 1930 with a famous letter to "Liebe Radioacktive Damen und Herren" (Dear radioactive ladies and gentlemen) at the Tubingen meeting of radioactivity researchers. Pauli's first public discussion of the neutrino was at the 7th Solvay Conference in Brussels in 1933.
The first experimental observation of the neutrino interacting with matter was made by Frederick Reines, Clyde Cowan, Jr, and collaborators in 1956 at the Savannah River Plant in South Carolina. Their neutrino source was a nuclear reactor (it actually produced antineutrinos from beta decay).
Modern neutrino detectors at IMB in Ohio and Kamiokande in Japan detected neutrinos from Supernova 1987A. A new neutrino detector at Sudbury, Ontario began collecting data in October of 1999. Another Japanese neutrino detector called Super Kamiokande became operational in April 1996.
An early set of experiments with a facility called the solar neutrino telescope, measured the rate of neutrino emission from the sun at only one third of the expected flux. Often referred to as the Solar Neutrino Problem, this deficiency of neutrinos has been difficult to explain. Recent results from the Sudbury Neutrino Observatory suggest that a fraction of the electron neutrinos produced by the sun are transformed into muon neutrinos on the way to the earth. The observations at Sudbury are consistent with the solar models of neutrino flux assuming that this "neutrino oscillation" is responsible for observation of neutrinos other than electron neutrinos.
The IceCube Neutrino Observatory will hunt for tiny particles that are common in the universe, but rarely interact with other matter. In fact, trillions of neutrinos pass through a person’s body each second. They rain down onto Earth as cosmic rays strike the upper atmosphere. Neutrinos also shoot out of the violent insides of stellar explosions, churn regularly from the sun and may even arise from the ambient leftovers of the Big Bang.
IceCube is tuned to find high-energy neutrinos like the ones bursting from active galactic nuclei, which are bright sources that are likely the radiation from a black hole gobbling the mass around it, and gamma ray bursts, intense beams of light from a star collapsing into a black hole. The $279 million observatory is a full cubic kilometer in volume, or 1,000 times bigger than the Super-Kamiokande neutrino detector in Japan. While IceCube is less sensitive than the Super-K, scientists will need the huge volume to see long streaks of muons, exotic leftovers from collisions between neutrinos and water nuclei.
IceCube’s sensors are designed to detect a flash of blue light when neutrinos collide with a water molecule. Ice at the South Pole is remarkably pure, so impinging neutrinos will almost certainly interact with water, not a different molecule. And because each new snowfall adds weight, packing down the ice below, there are a lot of molecules for a neutrino to hit.
Unlike most physics experiments, IceCube began taking data while under construction. Since 2005, it has already seen neutrinos with energies as high as 100 trillion electron-volts, seven times the maximum power that will be produced by collisions between protons at the Large Hadron Collider near Geneva, Switzerland.
Astrophysicists have a long list of scientific questions for IceCube to investigate during its planned 15-year life. For example, physicists believe that supernovas accelerate protons, but evidence is circumstantial. Seeing high-energy neutrinos, which should spew out of the bursting stars along with protons, would confirm theories of how stars explode.
“People have known for a long time it must be there, but to see it, and measure the right number, is an important thing to do,” says project spokesperson Tom Gaisser, a physicist at the University of Delaware in Newark.
Also on the wish list for scientists: finding neutrinos produced when hypothesized dark matter particles annihilate in the sun. Dark matter is thought to be much more abundant than ordinary matter in the universe, but has not yet been detected.
The electron neutrino (a lepton) was first postulated in 1930 by Wolfgang Pauli to explain why the electrons in beta decay were not emitted with the full reaction energy of the nuclear transition. The apparent violation of conservation of energy and momentum was most easily avoided by postulating another particle. Enrico Fermi called the particle a neutrino and developed a theory of beta decay based on it, but it was not experimentally observed until 1956.
Wolfgang Pauli introduced the neutrino to the world of physics in 1930 with a famous letter to "Liebe Radioacktive Damen und Herren" (Dear radioactive ladies and gentlemen) at the Tubingen meeting of radioactivity researchers. Pauli's first public discussion of the neutrino was at the 7th Solvay Conference in Brussels in 1933.
The first experimental observation of the neutrino interacting with matter was made by Frederick Reines, Clyde Cowan, Jr, and collaborators in 1956 at the Savannah River Plant in South Carolina. Their neutrino source was a nuclear reactor (it actually produced antineutrinos from beta decay).
Modern neutrino detectors at IMB in Ohio and Kamiokande in Japan detected neutrinos from Supernova 1987A. A new neutrino detector at Sudbury, Ontario began collecting data in October of 1999. Another Japanese neutrino detector called Super Kamiokande became operational in April 1996.
An early set of experiments with a facility called the solar neutrino telescope, measured the rate of neutrino emission from the sun at only one third of the expected flux. Often referred to as the Solar Neutrino Problem, this deficiency of neutrinos has been difficult to explain. Recent results from the Sudbury Neutrino Observatory suggest that a fraction of the electron neutrinos produced by the sun are transformed into muon neutrinos on the way to the earth. The observations at Sudbury are consistent with the solar models of neutrino flux assuming that this "neutrino oscillation" is responsible for observation of neutrinos other than electron neutrinos.
The IceCube Neutrino Observatory will hunt for tiny particles that are common in the universe, but rarely interact with other matter. In fact, trillions of neutrinos pass through a person’s body each second. They rain down onto Earth as cosmic rays strike the upper atmosphere. Neutrinos also shoot out of the violent insides of stellar explosions, churn regularly from the sun and may even arise from the ambient leftovers of the Big Bang.
IceCube is tuned to find high-energy neutrinos like the ones bursting from active galactic nuclei, which are bright sources that are likely the radiation from a black hole gobbling the mass around it, and gamma ray bursts, intense beams of light from a star collapsing into a black hole. The $279 million observatory is a full cubic kilometer in volume, or 1,000 times bigger than the Super-Kamiokande neutrino detector in Japan. While IceCube is less sensitive than the Super-K, scientists will need the huge volume to see long streaks of muons, exotic leftovers from collisions between neutrinos and water nuclei.
IceCube’s sensors are designed to detect a flash of blue light when neutrinos collide with a water molecule. Ice at the South Pole is remarkably pure, so impinging neutrinos will almost certainly interact with water, not a different molecule. And because each new snowfall adds weight, packing down the ice below, there are a lot of molecules for a neutrino to hit.
Unlike most physics experiments, IceCube began taking data while under construction. Since 2005, it has already seen neutrinos with energies as high as 100 trillion electron-volts, seven times the maximum power that will be produced by collisions between protons at the Large Hadron Collider near Geneva, Switzerland.
Astrophysicists have a long list of scientific questions for IceCube to investigate during its planned 15-year life. For example, physicists believe that supernovas accelerate protons, but evidence is circumstantial. Seeing high-energy neutrinos, which should spew out of the bursting stars along with protons, would confirm theories of how stars explode.
“People have known for a long time it must be there, but to see it, and measure the right number, is an important thing to do,” says project spokesperson Tom Gaisser, a physicist at the University of Delaware in Newark.
Also on the wish list for scientists: finding neutrinos produced when hypothesized dark matter particles annihilate in the sun. Dark matter is thought to be much more abundant than ordinary matter in the universe, but has not yet been detected.
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