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History Edit

In 1931, Nuclear Theorist Wolfgang Pauli, basing his prediction on the fact that energy and momentum did not appear to be conserved in certain radioactive decays, hypothsizes the idea of a new sub-atomic particle.This new particle carries off energy lost in the decay of certain atoms. Three years later in 1934, on of the future Manhattan Project members, Enrico Fermi, further investigates, and subsequently strengthens the possibility of the hypothesized particle. Fermi in fact invents the term Neutrino, which in Italian means little neutral one. Fermi is the first in a list of many physicists to ad to the theory of the Neutrino.

In 1959, Discovery of a particle fitting the expected characteristics of the neutrino is announced by Clyde Cowan and Fred Reines (a founding member of Super-Kamiokande; UCI professor emeritus and recipient of the 1995 Nobel Prize in physics for his contribution to the discovery). This neutrino is later determined to be the partner of the electron. Kamionade is the spearhead tool of the research following the Neutrino.

Three years later, Experiments at Brookhaven National Laboratory and CERN, the European Laboratory for Nuclear Physics make a surprising discovery: neutrinos produced in association with muons do not behave the same as those produced in association with electrons. They have, in fact, discovered a second type of neutrino (the muon neutrino). The first experiment to detect neutrinos occurs in 1959, was produced by the Sun's burning, using a liquid Chlorine target deep underground, reports that less than half the expected neutrinos are observed. This is the origin of the long-standing "solar neutrino problem." The possibility that the missing electron neutrinos may have transformed into another type (undetectable to this experiment) is soon suggested, but unreliability of the solar model on which the expected neutrino rates are based is initially considered a more likely explanation.

In 1978 The tau particle is discovered at SLAC, the Stanford Linear Accelerator Center. It is soon recognized to be a heavier version of the electron and muon, and its decay exhibits the same apparent imbalance of energy and momentum that led Pauli to predict the existence of the neutrino in 1931. The existence of a third neutrino associated with the tau is hence inferred, although this neutrino has yet to be directly observed.

In 1985 The IMB experiment, a large water detector searching for proton decay but which also detects neutrinos, notices that fewer muon-neutrino interactions than expected are observed. The anomaly is at first believed to be an artifact of detector inefficiencies. That same yearA Russian team reports measurement, for the first time, of a non-zero neutrino mass. The mass is extremely small (10,000 times less than the mass of the electron), but subsequent attempts to independently reproduce the measurement do not succeed.

Kamiokande, in 1987, another large water detector looking for proton decay, and IMB detect a simultaneous burst of neutrinos from Supernova 1987A. The next yearKamiokande, another water detector looking for proton decay but better able to distinguish muon neutrino interactions from those of electron neutrino, reports that they observe only about 60% of the expected number of muon-neutrino interactions.

Three events followed in the year 1989, The Frejus and NUSEX experiments, much smaller than either Kamiokande or IMB, and using iron rather than water as the neutrino target, report no deficit of muon-neutrino interactions. Following this, Experiments at CERN's Large Electron-Positron (LEP) accelerator determine that no additional neutrinos beyond the three already known can exist. Later that year, Kamiokande becomes the second experiment to detect neutrinos from the Sun, and confirms the long-standing anomaly by finding only about 1/3 the expected rate.

In 1990After an upgrade which improves the ability to identify muon-neutrino interactions, IMB confirms the deficit of muon neutrino interactions reported by Kamiokande. In 1994 Kamiokande finds a deficit of high-energy muon-neutrino interactions. Muon-neutrinos travelling the greatest distances from the point of production to the detector exhibit the greatest depletion. Later that year the Kamiokande and IMB groups collaborate to test the ability of water detectors to distinguish muon- and electron-neutrino interactions, using a test beam at the KEK accelerator laboratory. The results confirm the validity of earlier measurements. The two groups will go on to form the nucleus of the Super-Kamiokande project.

In 1996, The Super-Kamiokande detector begins operation, leading the find in 1998, which announces evidence of non-zero neutrino mass at the Neutrino '98 conference.

Masses & Types Edit

Neutrinos come in three types, or "flavors, they are the Electron, the Muon, and the Tau

Fermion Mass

Generation 1 (electron) Electron neutrino < 2.2 eV Electron antineutrino < 2.2 eV

Generation 2 (muon) Muon neutrino < 170 keV Muon antineutrino < 170 keV

Generation 3 (tau) Tau neutrino < 15.5 MeV Tau antineutrino < 15.5 MeV

The masses of these neutrinos are actually massless, yet have been proven to have infintessimily small masses, nearly indetectable.


Formulations Edit

Solar neutrinos They come along with the process of thermonuclear fusion inside the stars (our sun or any other star in the universe). Their energy is quite weak (some MeV) and they can travel in a long and quite way. They come from different nuclear reactions whose main reaction (85% of the solar neutrinos come from it) is:

P+P => H+e+(neutrino)

p is a proton, H is a deuterium nucleus, e is an anti-electron and the last one is a neutrino. Depending on the nuclear reaction concerned, the neutrino has not the same energy.

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