Editing Neutrino (section)

=== Pauli's proposal ===
The neutrino{{efn|
More specifically, Pauli postulated what is now called the ''electron neutrino''. Two other types were discovered later: see ''[[#Neutrino_flavors_anchor|Neutrino flavor]]'' below.
}} was postulated first by [[Wolfgang Pauli]] in 1930 to explain how beta decay could conserve [[conservation of energy|energy]], [[conservation of momentum|momentum]], and [[conservation of angular momentum|angular momentum]] ([[Spin (physics)|spin]]). In contrast to [[Niels Bohr]], who proposed a statistical version of the conservation laws to explain the observed [[Beta decay#Neutrinos|continuous energy spectra in beta decay]], Pauli hypothesized an undetected particle that he called a "neutron", using the same ''-on'' ending employed for naming both the [[proton]] and the [[electron]]. He considered that the new particle was emitted from the nucleus together with the electron or beta particle in the process of beta decay and had a mass similar to the electron.<ref name=Brown-1978-idea-ν>
{{cite journal
 |last=Brown 
 |first=Laurie M. 
 |author-link=Laurie Brown (physicist)
 |year=1978
 |title=The idea of the neutrino
 |journal=[[Physics Today]]
 |volume=31 
 |issue=9 
 |pages=23–28
 |bibcode=1978PhT....31i..23B 
 |doi=10.1063/1.2995181
}}
</ref>{{efn|
[[Niels Bohr]] was notably opposed to this interpretation of beta decay—he was ready to accept that energy, momentum, and angular momentum were not conserved quantities at the atomic level.
}}

[[James Chadwick]] discovered a much more massive neutral nuclear particle in 1932 and named it a [[neutron]] also, leaving two kinds of particles with the same name. The word "neutrino" entered the scientific vocabulary through [[Enrico Fermi]], who used it during a conference in Paris in July&nbsp;1932 and at the Solvay Conference in October&nbsp;1933, where Pauli also employed it. The name (the [[Italian language|Italian]] equivalent of "little neutral one") was jokingly coined by [[Edoardo 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 heavy neutron.<ref>
{{cite journal
 |last=Amaldi 
 |first=Edoardo
 |author-link=Edoardo Amaldi
 |year=1984
 |title=From the discovery of the neutron to the discovery of nuclear fission
 |journal=[[Physics Reports]]
 |volume=111 |issue=1–4 |page=306
 |bibcode=1984PhR...111....1A
 |doi=10.1016/0370-1573(84)90214-X
}}
</ref>

In [[Fermi's interaction|Fermi's theory of beta decay]], Chadwick's large neutral particle could decay to a proton, electron, and the smaller neutral particle (now called an ''electron antineutrino''):
: {{math| {{SubatomicParticle|Neutron0}} → {{SubatomicParticle|Proton+}} + {{SubatomicParticle|Electron-}} + {{SubatomicParticle|Electron antineutrino}} }}

Fermi's paper, written in 1934,<ref name=Fermi-1934/> unified Pauli's neutrino with [[Paul Dirac]]'s [[positron]] and [[Werner Heisenberg]]'s neutron–proton model and gave a solid theoretical basis for future experimental work.<ref name=Fermi-1934>
{{cite journal
 |last=Fermi
 |first=Enrico
 |author-link=Enrico Fermi
 |date=March 1934
 |title=Versuch einer Theorie der β-Strahlen. I
 |trans-title=Search for a theory of β-decay. I
 |journal=[[Zeitschrift für Physik A]]
 |language=de
 |volume=88
 |issue=3–4
 |pages=161–177
 |bibcode=1934ZPhy...88..161F
 |doi=10.1007/BF01351864
 |s2cid=125763380
}}</ref><ref>
{{cite journal
 |last=Wilson
 |first=Fred L.
 |date=1 December 1968
 |title=Fermi's theory of beta decay
 |journal=[[American Journal of Physics]]
 |volume=36
 |issue=12
 |pages=1150–1160
 |bibcode=1968AmJPh..36.1150W
 |doi=10.1119/1.1974382
 |url=http://microboone-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=953;filename=FermiBetaDecay1934.pdf;version=1
 |access-date=5 October 2011
 |archive-date=12 May 2013
 |archive-url=https://web.archive.org/web/20130512011303/http://microboone-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=953;filename=FermiBetaDecay1934.pdf;version=1
 |url-status=live
}}</ref><ref name=Close-2012-ν>
{{cite book
 |last=Close
 |first=Frank
 |date=12 April 2012
 |orig-date=2010
 |title=Neutrino
 |publisher=[[Oxford University Press]]
 |page=24
 |isbn=978-0-19-969599-7
}}</ref><!--{{rp|page=24}}-->

By 1934, there was experimental evidence against Bohr's idea that energy conservation is invalid for beta decay: At the [[Solvay conference]] of that year, measurements of the energy spectra of beta particles (electrons) were reported, showing that there is a strict limit on the energy of electrons from each type of beta decay. Such a limit is not expected if the conservation of energy is invalid, in which case any amount of energy would be statistically available in at least a few decays. The natural explanation of the beta decay spectrum as first measured in 1934 was that only a limited (and conserved) amount of energy was available, and a new particle was sometimes taking a varying fraction of this limited energy, leaving the rest for the beta particle. Pauli made use of the occasion to publicly emphasize that the still-undetected "neutrino" must be an actual particle.<ref name=Close-2012-ν/>{{rp|page=25}} The first evidence of the reality of neutrinos came in 1938 via simultaneous cloud-chamber measurements of the electron and the recoil of the nucleus.<ref>
{{cite news
 |title=Cloud-chamber test finds neutrino 'real'
 |date=22 May 1938
 |newspaper=[[The New York Times]]
 |url=https://www.nytimes.com/1938/05/22/archives/cloudchamber-test-finds-neutrino-real-drs-crane-and-halpern-decide.html?sq=%2522H.%2520Richard%2520Crane%2522&scp=1&st=cse
 |quote=Drs.&nbsp;Crane and Halpern decide it is no mere hypothesis
}}
</ref>