Neutrinos
The first use of a hydrogen bubble chamber to detect neutrinos, on 13 November 1970, at Argonne National Laboratory. A neutrino hits a proton in a hydrogen atom. The collision occurs at the point where three tracks emanate on the right of the photograph.
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| Composition | Elementary particle |
|---|---|
| Statistics | Fermionic |
| Generation | First, second and third |
| Interactions | Weak interaction and gravitation |
| Symbol |
ν e, ν μ, ν τ, ν e, ν μ, ν τ |
| Antiparticle | Opposite chirality from particle |
| Theorized |
ν τ (Tau neutrino): Mid 1970s |
| Discovered |
ν e: Clyde Cowan, Frederick Reines (1956) ν μ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962) ν τ: DONUT collaboration (2000) |
| Types | 3 – electron neutrino, muon neutrino and tau neutrino |
| Mass | ≤ 0.120 eV/c2 (95% confidence level, sum of 3 flavors) |
| Electric charge | 0 e |
| Spin | 1/2 |
| Weak isospin | LH: +1/2, RH: 0 |
| Weak hypercharge | LH: -1, RH: 0 |
| B − L | −1 |
| X | −3 |
ν
e (Electron neutrino): Wolfgang Pauli (1930)
ν
μ (Muon neutrino): Late 1940s
A neutrino (/nuːˈtriːnoʊ/ or /njuːˈtriːnoʊ/) (denoted by the Greek letter ν) is a fermion (an elementary particle with half-integer spin) that interacts only via the weak subatomic force and gravity. The mass of the neutrino is much smaller than that of the other known elementary particles.
The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was originally thought to be zero. The weak force has a very short range, gravity is extremely weak on the subatomic scale, and neutrinos, as leptons, do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.
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