Similarly, experiments measuring the flux of atmospheric neutrinos have also seen disagreement with theoretical expectations. All solar neutrino experiments performed to date have detected fewer electron neutrinos than are expected from standard solar models. We now discuss in some detail two particular energy ranges of interest-solar/atmospheric neutrinos and neutrinos at the highest energy frontier. During that second, the γ-ray burst outshines the entire remainder of the Universe. In these celestial explosions, detected at earth approximately once per day, a mass-energy equal to one solar mass is suddenly released in the space of approximately one second. Perhaps most spectacularly, neutrinos may provide essential information about the nature of γ-ray bursts. Neutrinos are also likely to be the primary experimental tool in understanding Active Galactic Nuclei, the extremely luminous, high mass (10 billion solar masses) black holes at the centers of many galaxies. Therefore, there is speculation that they may be caused by neutrinos. If they are photons, protons, or any other “conventional” cosmic ray source, the nearest known high-energy cosmic accelerators are so far away that photons or protons produced by them should be absorbed before reaching the earth. The origin of these cosmic rays, a factor of 100 million times more energetic than particles capable of being produced by terrestrial accelerators, is unknown. For the future, neutrinos may hold the key to solving the puzzles of Dark Matter (the fact that most of the mass in the universe is nonluminous a large fraction of that mass may actually be in the form of massive neutrinos) and the the origin of the highest energy cosmic rays. the antineutrino ( ii) the discovery of different types of neutrinos, which interacted very distinctly (1962) ( iii) the detection of substantially fewer electron neutrinos from the sun than our model of the sun accommodated (beginning in 1968) and ( iv) evidence for a nonzero neutrino mass (first unambiguously claimed in 1998). Wu at Columbia, which is intimately connected with the intrinsic “handedness” of the neutrino vs. Since then, the neutrino has had an illustrious history: ( i) the discovery of parity violation in 1957 by C. Pauli invoked the neutrino as an undetected, massless particle that carried away this missing energy and momentum. Similarly, momentum appeared to be violated in the reaction. In the decay of a neutron into a proton and an electron, it was realized that the final state proton and electron energies did not add up to the initial neutron energy. However, the inertness of the neutrino immediately presents an experimental challenge: one must use an extremely large volume of material to detect the very rare neutrino interactions.īecause of its inertness, evidence for the neutrino was not uncovered until 1931, when Pauli posited the neutrino to solve a long-standing experimental problem of β decay. ‖ Alternatively, neutrinos from the edge of the Universe will easily penetrate the interstellar medium without being absorbed or deflected. This represents a unique experimental opportunity-neutrinos from the sun carry direct information about the solar interior. A typical neutrino produced in the interior of the sun will travel unscathed through a light-year of lead before interacting. Neutrinos interact only by means of the “weak” interactions, which are, indeed, quite weak. Neutrinos are also the most inert of the presently known fundamental particles because they have no electric charge, they do not particpate in either electric or magnetic interactions unlike quarks, they do not participate in the “strong nuclear force” that holds the proton together and is responsible for the awesome explosive force of a hydrogen bomb. ¶ This is contrasted with protons, e.g., which are believed to contain three smaller quarks. Neutrinos are “fundamental” particles in the sense that, like quarks or electrons, they are believed to have no constituents.

Neutrino bomb