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Originally Posted by dipayankar  So as of now it is not conclusive. What characteristics would make people think that they have mass?? |
Hi Dipayankar; This might help answer your question. Historic Dispute : Do neutrinos have mass? Viewpoint: Yes, the Japanese-U.S. research team called the Super-Kamiokande Collaboration announced experiment results in 1998 that proved that neutrinos do indeed have mass.
Viewpoint: No, the experiments of earlier twentieth-century scientists repeatedly indicated that neutrinos did not have mass.
In 1931 Wolfgang Pauli first predicted the existence of a subatomic particle that Enrico Fermi would later name the neutrino. The neutrino must exist, Pauli reasoned, because otherwise the atomic process known as beta decay would violate the physical laws of conservation of energy and conservation of angular momentum. Neutrinos had never been detected, so Pauli concluded that they didn't interact with most other particles or forces. This implied they were extremely small particles with no charge or mass.
The only force that noticeably affects neutrinos is the "weak" force, a subatomic force that is not as strong as the force that holds the atomic nucleus together, but that likewise operates only at very short range. Because of their extremely limited interactions with other particles and forces, neutrinos can travel huge distances unimpeded by anything in their path. Neutrinos arising from the nuclear reactions in the Sun stream through Earth and all its inhabitants without having any effect whatsoever. For this reason they are extremely difficult to detect, and their existence was not confirmed until a quarter century after Pauli's prediction.
Today's neutrino detectors, kept deep underground to avoid stray particles on Earth's surface, may contain thousands of tons of fluid. While trillions of neutrinos pass through the fluid every day, only a few dozen are likely to be detected.
Scientists have discovered that there are three types of neutrinos, each associated with a different charged particle for which it is named. Thus they are called the electron neutrino, muon neutrino, and tau neutrino. The first type of neutrino to be discovered was the electron neutrino, in 1959. The muon neutrino was discovered in 1962. The tau neutrino has yet to be directly observed. It was inferred from the existence of the tau particle itself, which was discovered in 1978. The tau particle is involved in decay reactions with the same imbalance that Pauli solved for beta decay by postulating the electron neutrino.
One ongoing issue in neutrino research is called the "solar neutrino problem." This refers to the detection of fewer electron neutrinos than expected, given the known energy output of the Sun. One possible explanation for this phenomenon could be "oscillation" between the different neutrino types. That is, electron neutrinos could change into muon or tau neutrinos, which are even more difficult to detect. Similarly, scientists have observed a deficit in the number of muon neutrinos they would expect to see coming from cosmic rays.
Neutrino oscillations, if they exist, are a quantum mechanical phenomenon dependent on the difference in the masses of the two types of particles. That means that if researchers could prove that neutrino oscillation occurs, at least one of the neutrino types involved must have a non-zero mass. In 1998 a Japanese-U.S. research team called the Super-Kamiokande Collaboration announced that they had discovered evidence of oscillation between muon neutrinos and either the tau neutrino or a new, unknown type.
Best to you, Pat
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