Electron neutrino

Electron neutrino
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	0e
Color charge	No
Spin	⁠1/2⁠ħ
Weak isospin	⁠1/2⁠
Weak hypercharge	−1
Chirality	left-handed (for right-handed neutrinos, seesterile neutrino)

Theelectron neutrino( $ν e$ ) is anelementary particlewhich has zeroelectric chargeand aspinof1⁄2.Together with theelectron,it forms the firstgenerationofleptons,hence the nameelectronneutrino.It was first hypothesized byWolfgang Pauliin 1930, to account formissing momentumandmissing energyinbeta decay,and was discovered in 1956 by a team led byClyde CowanandFrederick Reines(seeCowan–Reines neutrino experiment).^[1]

Proposal

In the early 1900s, theories predicted that the electrons resulting frombeta decayshould have been emitted at a specific energy. However, in 1914,James Chadwickshowed that electrons were instead emitted in a continuous spectrum.^[1]

n⁰
→
p⁺
+
e⁻

The early understanding of beta decay

In 1930,Wolfgang Paulitheorized that an undetected particle was carrying away the observed difference between theenergy,momentum,andangular momentumof the initial and final particles.^[a]^[2]

n 0 \to p + + e - + ν 0 e

Pauli's version of beta decay

Pauli's letter

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-14andLi-6nuclei, 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 spin⁠1/2⁠and obey theexclusion principle,and additionally differ fromlight quantain 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 inβdecay 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 aγray.
I admit that my remedy may appear to have a smalla prioriprobability 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]

Discovery

The electron neutrino was discovered byClyde CowanandFrederick Reinesin 1956.^[1]

Name

Pauli originally named his proposed light particle aneutron.WhenJames Chadwickdiscovered 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 termneutrinoin 1934 (it was jokingly coined byEdoardo Amaldiduring 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 apunonneutrone,theItalianequivalent ofneutron:the-oneending can be anaugmentativein Italian, soneutronecould be read as the "large neutral thing";-inoreplaces the augmentative suffix with adiminutiveone ( "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.

Electron antineutrino

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 physicsis 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 decayand other types ofweak interactions.

Notes

^Niels Bohrwas notably opposed to this interpretation of beta decay and was ready to accept that energy, momentum, and angular momentum were not conserved quantities.
^Pauli means what was later named "neutrino". See§ Name,above.

References

^^a ^b ^c ^d "The Reines-Cowan Experiments: Detecting the Poltergeist"(PDF).Los Alamos Science.25:3. 1997.Retrieved2010-02-10.
^ K. Riesselmann (2007)."Logbook: Neutrino Invention".Symmetry Magazine.4(2). Archived fromthe originalon 2009-05-31.
^ Brown, L.M. (1978). "The idea of the neutrino".Physics Today.31(9): 23–28.Bibcode:1978PhT....31i..23B.doi:10.1063/1.2995181.
^ M.F. L'Annunziata (2007).Radioactivity.Elsevier.p. 100.ISBN 978-0-444-52715-8.