| Composition | Elementary particle |
|---|---|
| Statistics | Fermionic |
| Family | Lepton |
| Generation | First |
| Interactions | Weak,Gravity |
| Symbol | ν e |
| Antiparticle | Electron antineutrino (ν e) |
| Theorized | Wolfgang Pauli (1930) |
| Discovered | Clyde Cowan,Frederick Reines (1956) |
| Mass | Small but non-zero. Seeneutrino mass. |
| Electric charge | 0 e |
| Color charge | No |
| Spin | 1/2 ħ |
| Weak isospin | 1/2 |
| Weak hypercharge | −1 |
| Chirality | left-handed (for right-handed neutrinos, seesterile neutrino) |
Theelectron neutrino (ν
e) is anelementary particle which has zeroelectric charge and aspin of1⁄2. Together with theelectron, it forms the firstgeneration ofleptons, hence the nameelectronneutrino. It was first hypothesized byWolfgang Pauli in 1930, to account formissing momentum andmissing energy inbeta decay, and was discovered in 1956 by a team led byClyde Cowan andFrederick Reines (seeCowan–Reines neutrino experiment).[1]
In the early 1900s, theories predicted that the electrons resulting frombeta decay should have been emitted at a specific energy. However, in 1914,James Chadwick showed that electrons were instead emitted in a continuous spectrum.[1]
In 1930,Wolfgang Pauli theorized that an undetected particle was carrying away the observed difference between theenergy,momentum, andangular momentum of the initial and final particles.[a][2]
On 4 December 1930, Pauli wrote a letter to the Physical Institute of theFederal Institute of Technology,Zürich, in which he proposed the electron "neutron" [neutrino] as a potential solution to solve the problem of the continuous beta decay spectrum. A translated excerpt of his letter reads:[1]
Dear radioactive ladies and gentlemen,
As the bearer of these lines [...] will explain more exactly, considering the 'false' statistics ofN-14 andLi-6 nuclei, as well as the continuousβ-spectrum, I have hit upon a desperate remedy to save the "exchange theorem" of statistics and the energy theorem. Namely [there is] the possibility that there could exist in the nuclei electrically neutral particles that I wish to call neutrons,[b] which have spin 1/2 and obey theexclusion principle, and additionally differ fromlight quanta in that they do not travel with the velocity of light: The mass of the neutron must be of the same order of magnitude as the electron mass and, in any case, not larger than 0.01 proton mass. The continuousβ-spectrum would then become understandable by the assumption that inβ decay a neutron is emitted together with the electron, in such a way that the sum of the energies of neutron and electron is constant.
[...]
But I don't feel secure enough to publish anything about this idea, so I first turn confidently to you, dear radioactives, with a question as to the situation concerning experimental proof of such a neutron, if it has something like about 10 times the penetrating capacity of aγ ray.
I admit that my remedy may appear to have a smalla priori probability because neutrons, if they exist, would probably have long ago been seen. However, only those who wager can win, and the seriousness of the situation of the continuousβ-spectrum can be made clear by the saying of my honored predecessor in office,Mr. Debye, [...] "One does best not to think about that at all, like the new taxes." [...] So, dear radioactives, put it to test and set it right. [...]
- With many greetings to you, also toMr. Back,
- Your devoted servant,
- W. Pauli
A translated reprint of the full letter can be found in the September 1978 issue ofPhysics Today.[3]
The electron neutrino was discovered byClyde Cowan andFrederick Reines in 1956.[1]
Pauli originally named his proposed light particle aneutron. WhenJames Chadwick discovered a much more massive nuclear particle in 1932 and also named it aneutron, this left the two particles with the same name.Enrico Fermi, who developed the theory ofbeta decay, introduced the termneutrino in 1934 (it was jokingly coined byEdoardo Amaldi during a conversation with Fermi at the Institute of physics of via Panisperna in Rome, in order to distinguish this light neutral particle from Chadwick's neutron) to resolve the confusion. It was apun onneutrone, theItalian equivalent ofneutron: the-one ending can be anaugmentative in Italian, soneutrone could be read as the "large neutral thing";-ino replaces the augmentative suffix with adiminutive one ("small neutral thing").[4]
Upon the prediction and discovery of a second neutrino, it became important to distinguish between different types of neutrinos. Pauli's neutrino is now identified as theelectron neutrino, while the second neutrino is identified as themuon neutrino.
The electron neutrino has a correspondingantiparticle, the electronantineutrino (ν
e), which differs only in that some of its properties haveequal magnitude but opposite sign. One major open question inparticle physics is whether neutrinos and anti-neutrinos are the same particle.[citation needed] If so, they would beMajorana fermions, whereas if not, they would beDirac fermions. They are produced inbeta decay and other types ofweak interactions.
| Elementary |
| ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Composite |
| ||||||||||||||||||||||||
| Quasiparticles | |||||||||||||||||||||||||
| Lists | |||||||||||||||||||||||||
| Related | |||||||||||||||||||||||||
