Neutrino: Difference between revisions

| generation = First ({{math|{{SubatomicParticle|Electron neutrino}}}}), second ({{math|{{SubatomicParticle|Muon neutrino}}}}), and third ({{math|{{SubatomicParticle|Tau neutrino}}}})

| interaction = [[Weak interaction]] and [[gravitation]]

| theorized = {{plainlist|

* {{math|{{SubatomicParticle|Electron neutrino}}}}, [[electron neutrino]]: [[Wolfgang Pauli]] (1930)

}}

| symbol = {{math|{{SubatomicParticle|Electron neutrino}}}} , {{math|{{SubatomicParticle|Muon neutrino}}}} , {{math|{{SubatomicParticle|Tau neutrino}}}} , {{math|{{SubatomicParticle|Electron antineutrino}}}} , {{math|{{SubatomicParticle|Muon antineutrino}}}} , {{math|{{SubatomicParticle|Tau antineutrino}}}}

{{cite journal

|first1=Susanne |last1=Mertens

|arxiv=1605.01579 |bibcode=2016JPhCS.718b2013M

|doi=10.1088/1742-6596/718/2/022013 |s2cid=56355240

| decay_time =

| decay_particle =

</ref>

 

 

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.

 

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''):

 

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>

</ref>

 

[[File:Clyde Cowan.jpg|thumb|upright|Fred Reines and Clyde Cowan conducting the neutrino experiment c. 1956]]

In 1942, [[Wang Ganchang]] first proposed the use of [[Electron capture|beta capture]] to experimentally detect neutrinos.<ref>

 

In this experiment, now known as the [[Cowan–Reines neutrino experiment]], antineutrinos created in a nuclear reactor by beta decay reacted with protons to produce [[neutron]]s and positrons:

 

The positron quickly finds an electron, and they [[Annihilation|annihilate]] each other. The two resulting [[gamma ray]]s (γ) are detectable. The neutron can be detected by its capture on an appropriate nucleus, releasing a gamma ray. The coincidence of both events—positron annihilation and neutron capture—gives a unique signature of an antineutrino interaction.

</ref>

 

The antineutrino discovered by [[Clyde Cowan]] and [[Frederick Reines]] was the antiparticle of the electron neutrino.

 

</ref>

 

{{Main|Solar neutrino problem}}

In the 1960s, the now-famous [[Homestake experiment]] made the first measurement of the flux of electron neutrinos arriving from the core of the Sun and found a value that was between one third and one half the number predicted by the [[Standard Solar Model]]. This discrepancy, which became known as the [[solar neutrino problem]], remained unresolved for some thirty years, while possible problems with both the experiment and the solar model were investigated, but none could be found. Eventually, it was realized that both were actually correct and that the discrepancy between them was due to neutrinos being more complex than was previously assumed. It was postulated that the three neutrinos had nonzero and slightly different masses, and could therefore oscillate into undetectable flavors on their flight to the Earth. This hypothesis was investigated by a new series of experiments, thereby opening a new major field of research that still continues. Eventual confirmation of the phenomenon of neutrino oscillation led to two Nobel prizes, one to [[Raymond Davis, Jr.|R. Davis]], who conceived and led the Homestake experiment and [[Masatoshi Koshiba]] of Kamiokande, whose work confirmed it, and one to [[Takaaki Kajita]] of Super-Kamiokande and [[Arthur B. McDonald|A.B. McDonald]] of [[Sudbury Neutrino Observatory|SNO]] for their joint experiment, which confirmed the existence of all three neutrino flavors and found no deficit.<ref name=CERN-2001-12-04-SNO/>

 

{{main|Neutrino oscillation}}

A practical method for investigating neutrino oscillations was first suggested by [[Bruno Pontecorvo]] in 1957 using an analogy with [[kaon]] oscillations; over the subsequent 10&nbsp;years, he developed the mathematical formalism and the modern formulation of vacuum oscillations. In 1985 [[Stanislav Mikheyev]] and [[Alexei Smirnov (physicist)|Alexei Smirnov]] (expanding on 1978 work by [[Lincoln Wolfenstein]]) noted that flavor oscillations can be modified when neutrinos propagate through matter. This so-called [[Mikheyev–Smirnov–Wolfenstein effect]] (MSW effect) is important to understand because many neutrinos emitted by fusion in the Sun pass through the dense matter in the [[solar core]] (where essentially all solar fusion takes place) on their way to detectors on Earth.

</ref> [[Takaaki Kajita]] of Japan, and [[Arthur B. McDonald]] of Canada, received the 2015 Nobel Prize for Physics for their landmark finding, theoretical and experimental, that neutrinos can change flavors.

 

{{main|cosmic neutrino background|diffuse supernova neutrino background}}

As well as specific sources, a general background level of neutrinos is expected to pervade the universe, theorized to occur due to two main sources.

 

 

Around 1&nbsp;second after the [[Big Bang]], neutrinos decoupled, giving rise to a background level of neutrinos known as the [[cosmic neutrino background]] (CNB).

 

 

[[Raymond Davis, Jr.|R. Davis]] and [[Masatoshi Koshiba|M. Koshiba]] were jointly awarded the 2002 Nobel Prize in Physics. Both conducted pioneering work on [[solar neutrino]] detection, and Koshiba's work also resulted in the first real-time observation of neutrinos from the [[SN 1987A]] supernova in the nearby [[Large Magellanic Cloud]]. These efforts marked the beginning of [[neutrino astronomy]].<ref name=Pagliarl-Vissani-etal-2009>

[[SN 1987A]] represents the only verified detection of neutrinos from a supernova. However, many stars have gone supernova in the universe, leaving a theorized [[diffuse supernova neutrino background]].

 

Neutrinos have half-integer [[Spin (physics)|spin]] ({{sfrac| 1 |2}}{{math|''ħ''}}); therefore they are [[fermion]]s. Neutrinos are leptons. They have only been observed to interact through the [[weak nuclear force|weak force]], although it is assumed that they also interact gravitationally. Since they have non-zero mass, theoretical considerations permit neutrinos to interact magnetically, but do not require them to. As yet there is no experimental evidence for a non-zero [[magnetic moment]] in neutrinos.

 

<!-- "Neutrino flavor" redirects here -->

Weak interactions create neutrinos in one of three leptonic [[Flavor (particle physics)|flavors]]: electron neutrinos ({{math|{{SubatomicParticle|Electron neutrino}}}}), muon neutrinos ({{math|{{SubatomicParticle|Muon neutrino}}}}), or [[tau neutrino]]s ({{math|{{SubatomicParticle|Tau neutrino}}}}), associated with the corresponding charged leptons, the [[electron]] ({{math|{{SubatomicParticle|Electron}}}}), [[muon]] ({{math|{{SubatomicParticle|Muon}}}}), and [[tau (particle)|tau]] ({{math|{{SubatomicParticle|Tau}}}}), respectively.<ref name=Nakamura-Petcov-PDG-2016-νmix>

Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses; each neutrino flavor state is a linear combination of the three discrete mass eigenstates. Although only differences of squares of the three mass values are known as of 2016,<ref name=Capozzi-Lisi-Marrone-etal-2016/> experiments have shown that these masses are tiny compared to any other particle. From [[cosmology|cosmological]] measurements, it has been calculated that the sum of the three neutrino masses must be less than one-millionth that of the electron.<ref name=Mertens-2016-mν/><ref name=Olive-PDG-2016-Σmν/>

 

{{cite web

|title=Neutrino mass hierarchy

</ref>

 

{{Main|Neutrino oscillation}}

Neutrinos [[Neutrino oscillation|oscillate]] between different flavors in flight. For example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino, as defined by the flavor of the charged lepton produced in the detector. This oscillation occurs because the three mass state components of the produced flavor travel at slightly different speeds, so that their quantum mechanical [[wave packet]]s develop relative [[Phase (waves)#phase shift|phase shift]]s that change how they combine to produce a varying superposition of three flavors. Each flavor component thereby oscillates as the neutrino travels, with the flavors varying in relative strengths. The relative flavor proportions when the neutrino interacts represent the relative probabilities for that flavor of interaction to produce the corresponding flavor of charged lepton.<ref name=Grossman-Lipkin-1997/><ref name=Bilenky-2016-ν-osc/>

</ref>

 

{{Main|Mikheyev–Smirnov–Wolfenstein effect}}

Neutrinos traveling through matter, in general, undergo a process analogous to [[Speed of light#In a medium|light traveling through a transparent material]]. This process is not directly observable because it does not produce [[ionizing radiation]], but gives rise to the [[Mikheyev–Smirnov–Wolfenstein effect]]. Only a small fraction of the neutrino's energy is transferred to the material.<ref>

</ref>

 

{{antimatter}}

For each neutrino, there also exists a corresponding [[antiparticle]], called an ''antineutrino'', which also has no electric charge and half-integer spin. They are distinguished from the neutrinos by having opposite signs of [[lepton number]] and opposite [[Chirality (physics)|chirality]] (and consequently opposite-sign weak isospin). As of 2016, no evidence has been found for any other difference.

|place=Paris, FR

|url=http://www.apc.univ-paris7.fr/AAP2007/

|archive-url=https://web.archive.org/web/20071112083328/http://www.apc.univ-paris7.fr/AAP2007/

</ref>

 

{{See also|Seesaw mechanism}}

Because antineutrinos and neutrinos are neutral particles, it is possible that they are the same particle. Rather than conventional [[Dirac fermion]]s, neutral particles can be another type of spin&nbsp;{{sfrac| 1 |2}} particle called ''[[Majorana particle]]s'', named after the Italian physicist [[Ettore Majorana]] who first proposed the concept. For the case of neutrinos this theory has gained popularity as it can be used, in combination with the [[seesaw mechanism]], to explain why neutrino masses are so small compared to those of the other elementary particles, such as electrons or quarks. Majorana neutrinos would have the property that the neutrino and antineutrino could be distinguished only by chirality; what experiments observe as a difference between the neutrino and antineutrino could simply be due to one particle with two possible chiralities.

|doi=10.1155/2016/6194250 |issn=1687-7357

|arxiv=1508.05759 |s2cid=10721441

</ref> and [[CUORE]].<ref>

{{cite journal

</ref>

 

Neutrinos can interact with a nucleus, changing it to another nucleus. This process is used in radiochemical [[neutrino detector]]s. In this case, the energy levels and spin states within the target nucleus have to be taken into account to estimate the probability for an interaction. In general the interaction probability increases with the number of neutrons and protons within a nucleus.<ref name=CERN-2001-12-04-SNO>

{{cite periodical

|publisher=[[European Center for Nuclear Research]]

|url=http://cerncourier.com/cws/article/cern/28553

}}

</ref><ref name=Kelić-Zinner-Kolbe-etal-2005/>

It is very hard to uniquely identify neutrino interactions among the natural background of radioactivity. For this reason, in early experiments a special reaction channel was chosen to facilitate the identification: the interaction of an antineutrino with one of the hydrogen nuclei in the water molecules. A hydrogen nucleus is a single proton, so simultaneous nuclear interactions, which would occur within a heavier nucleus, do not need to be considered for the detection experiment. Within a cubic meter of water placed right outside a nuclear reactor, only relatively few such interactions can be recorded, but the setup is now used for measuring the reactor's plutonium production rate.

 

 

{| class="wikitable floatright"

|+Neutrinos in the Standard Model of elementary particles

the shorter the lifetime of the Z&nbsp;boson. Measurements of the Z lifetime have shown that three light neutrino flavors couple to the Z.<ref name=Nakamura-Petcov-PDG-2016-νmix/> The correspondence between the six [[quark]]s in the Standard Model and the six leptons, among them the three neutrinos, suggests to physicists' intuition that there should be exactly three types of neutrino.

 

There are several active research areas involving the neutrino with aspirations of finding:

* the three neutrino mass values

* evidence of physics which might break the Standard Model of [[particle physics]], such as [[neutrinoless double beta decay]], which would be evidence for violation of lepton number conservation.

 

International scientific collaborations install large neutrino detectors near nuclear reactors or in neutrino beams from particle accelerators to better constrain the neutrino masses and the values for the magnitude and rates of oscillations between neutrino flavors. These experiments are thereby searching for the existence of [[CP violation]] in the neutrino sector; that is, whether or not the laws of physics treat neutrinos and antineutrinos differently.<ref name=Capozzi-Lisi-Marrone-etal-2016/>

 

|archive-date=2018-06-16

|archive-url=https://web.archive.org/web/20180616053311/http://www.pro-physik.de/details/physiknews/11069692/Die_Neutrino-Waage_geht_in_Betrieb.html

</ref> to determine the value of the mass of the electron neutrino, with other approaches to this problem in the planning stages.<ref name=Mertens-2016-mν/>

 

Despite their tiny masses, neutrinos are so numerous that their gravitational force can influence other matter in the universe.

 

</ref>

 

Other efforts search for evidence of a [[sterile neutrino]]—a fourth neutrino flavor that would not interact with matter like the three known neutrino flavors.<ref>

{{cite magazine

|volume=7 |issue=10 |page=360

|arxiv=2109.13541 |doi=10.3390/universe7100360

|doi-access=free

</ref>

 

According to an analysis published in 2010, data from the [[Wilkinson Microwave Anisotropy Probe]] of the [[Cosmic microwave background|cosmic background radiation]] is compatible with either three or four types of neutrinos.<ref>{{cite magazine |first=Ron |last=Cowen |date=2 February 2010 |title=New look at Big Bang radiation refines age of universe |url=https://www.wired.com/2010/02/nasa-wmap-universe-age/ |magazine=[[Wired (magazine)|Wired]] |access-date=2016-11-01 }}</ref>

 

Another hypothesis concerns "neutrinoless double-beta decay", which, if it exists, would violate lepton number conservation. Searches for this mechanism are underway but have not yet found evidence for it. If they were to, then what are now called antineutrinos could not be true antiparticles.

 

[[Cosmic ray]] neutrino experiments detect neutrinos from space to study both the nature of neutrinos and the cosmic sources producing them.<ref name="IceCube">{{cite press release |title=IceCube Research Highlights |url=https://icecube.wisc.edu/science/highlights |collaboration=IceCube Collaboration |publisher=[[University of Wisconsin–Madison]] |access-date=13 December 2016}}</ref>

 

{{Main|Measurements of neutrino speed}}

 

|doi=10.1103/PhysRevLett.107.181803 |pmid=22107624

|arxiv=1109.6562 |bibcode=2011PhRvL.107r1803C

</ref>

 

{{main|Faster-than-light neutrino anomaly}}

 

In September&nbsp;2011, the [[OPERA experiment|OPERA collaboration]] released calculations showing velocities of 17&nbsp;GeV and 28&nbsp;GeV neutrinos exceeding the speed of light in their experiments. In November&nbsp;2011, OPERA repeated its experiment with changes so that the speed could be determined individually for each detected neutrino. The results showed the same faster-than-light speed. In February&nbsp;2012, reports came out that the results may have been caused by a loose fiber optic cable attached to one of the atomic clocks which measured the departure and arrival times of the neutrinos. An independent recreation of the experiment in the same laboratory by [[ICARUS experiment|ICARUS]] found no discernible difference between the speed of a neutrino and the speed of light.<ref name=Antonlo-Aprli-Baibusnv-etal-2012/>

 

{{unsolved|physics|Can we measure the neutrino masses? Do neutrinos follow [[Fermi–Dirac statistics|Dirac]] or [[Majorana fermion|Majorana]] statistics?}}

[[File:NeutrinoMassTimeline2022.webp|thumb|left|Timeline of neutrino mass measurements by different experiments<ref name=KATRIN-2022-NatPhys/>]]

|publisher=Cambridge University Press

}}

{{cite journal

|last1=Schechter |first1=Joseph

|pages=A6

|arxiv=1807.06209 |doi=10.1051/0004-6361/201833910

|s2cid=119335614

{{cite journal

|last1=Di Valentino |first1=Eleonora

|year=2021

|title=On the most constraining cosmological neutrino mass bounds

|page=083504

|s2cid=235669844

{{cite journal

|last1=Di Valentino |first1=Eleonora

|arxiv=2112.02993

|title=Neutrino Mass Bounds in the Era of Tension Cosmology

|year=2022

|volume=931

|s2cid=244909022

|doi-access=free

 

The Nobel prize in Physics 2015 was awarded to Takaaki Kajita and Arthur B. McDonald for their experimental discovery of neutrino oscillations, which demonstrates that neutrinos have mass.<ref>

|publisher=The Royal Swedish Academy of Sciences

|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/2015/press.html

{{cite news

|first=Charles |last=Day

|doi=10.1103/PhysRevLett.117.082503 |bibcode=2016PhRvL.117h2503G

|pmid=27588852 |arxiv=1605.02889

 

{{main|Sterile neutrino}}

Experimental results show that within the margin of error, all produced and observed neutrinos have left-handed [[Helicity (particle physics)|helicities]] (spins antiparallel to [[Momentum|momenta]]), and all antineutrinos have right-handed helicities.<ref>

|publisher=[[Particle Data Group]]

|url=http://pdg.lbl.gov/2006/reviews/numixrpp.pdf

</ref><ref>

{{cite journal

</ref>

 

{{Main|GSI anomaly}}

An unexpected series of experimental results for the rate of decay of heavy [[Highly charged ion|highly charged]] radioactive [[ion]]s circulating in a [[storage ring]] has provoked theoretical activity in an effort to find a convincing explanation.

 

The rates of weak decay of two radioactive species with half lives of about 40&nbsp;seconds and 200&nbsp;seconds were found to have a significant oscillatory [[modulation]], with a period of about 7&nbsp;seconds.<ref name=Kienle-Bosch-Bühler-etal-2013/>

{{cite journal

|last=Giunti |first=Carlo

|issn=2073-8994 |doi=10.3390/sym8060049

|arxiv=1407.1789 |s2cid=14287612 |bibcode=2016Symm....8...49G

</ref>

 

 

Nuclear reactors are the major source of human-generated neutrinos. The majority of energy in a nuclear reactor is generated by fission (the four main fissile isotopes in nuclear reactors are {{SimpleNuclide|uranium|235|link=yes}}, {{SimpleNuclide|uranium|238|link=yes}}, {{SimpleNuclide|plutonium|239|link=yes}} and {{SimpleNuclide|plutonium|241|link=yes}}), the resultant neutron-rich daughter nuclides rapidly undergo additional beta decays, each converting one neutron to a proton and an electron and releasing an electron antineutrino. Including these subsequent decays, the average nuclear fission releases about {{val|200|u=MeV}} of energy, of which roughly 95.5% remains in the core as heat, and roughly 4.5% (or about {{val|9|u=MeV}})<ref>

{{cite book

|access-date=2009-06-25

|archive-url=https://web.archive.org/web/20060425181600/http://www.kayelaby.npl.co.uk/

</ref> is radiated away as antineutrinos. For a typical nuclear reactor with a thermal power of {{val|4000|ul=MW}},{{efn|

Like all [[thermal power plant]]s, only about one third of the heat generated can be converted to electricity, so a {{val|4000|u=MW}} reactor would produce only {{val|1300|u=MW}} of electric power, with {{val|2700|u=MW}} being [[waste heat]].

An estimated 3% of all antineutrinos from a nuclear reactor carry an energy above that threshold. Thus, an average nuclear power plant may generate over {{val|e=20}} antineutrinos per second above the threshold, but also a much larger number ({{nobr|97%&thinsp;/&thinsp;3% ≈ 30&nbsp;times}} this number) below the energy threshold; these lower-energy antineutrinos are invisible to present detector technology.

 

{{main|Accelerator neutrinos}}

Some [[particle accelerator]]s have been used to make neutrino beams. The technique is to collide [[proton]]s with a fixed target, producing charged [[pion]]s or [[kaon]]s. These unstable particles are then magnetically focused into a long tunnel where they decay while in flight. Because of the [[Lorentz transformation|relativistic boost]] of the decaying particle, the neutrinos are produced as a beam rather than isotropically. Efforts to design an accelerator facility where neutrinos are produced through muon decays are ongoing.<ref name=Bandypdhy-Choubey-Gandhi-Goswami-etal-2009/> Such a setup is generally known as a [[Neutrino Factory|"neutrino factory"]].

 

Unlike other artificial sources, colliders produce both neutrinos and anti-neutrinos of all flavors at very high energies. The first direct observation of collider neutrinos was reported in 2023 by the [[FASER experiment]] at the [[Large Hadron Collider]].<ref name="colliderneutrino">{{cite journal |last1=Worcester |first1=Elizabeth |title=The Dawn of Collider Neutrino Physics |journal=Physics |date=July 19, 2023 |volume=16 |page=113 |doi=10.1103/Physics.16.113 |bibcode=2023PhyOJ..16..113W |s2cid=260749625 |access-date=July 23, 2023 |url=https://physics.aps.org/articles/v16/113|doi-access=free }}</ref>

 

[[Nuclear weapon]]s also produce very large quantities of neutrinos. [[Fred Reines]] and [[Clyde Cowan]] considered the detection of neutrinos from a bomb prior to their search for reactor neutrinos; a fission reactor was recommended as a better alternative by Los Alamos physics division leader J.M.B. Kellogg.<ref>

{{cite journal

</ref> Fission weapons produce antineutrinos (from the fission process), and fusion weapons produce both neutrinos (from the fusion process) and antineutrinos (from the initiating fission explosion).

 

{{main|Geoneutrino}}

Neutrinos are produced together with the natural [[background radiation]]. In particular, the decay chains of {{SimpleNuclide|uranium|238|link=yes}} and {{SimpleNuclide|thorium|232|link=yes}} isotopes, as well as {{SimpleNuclide|potassium|40|link=yes}}, include beta decays which emit antineutrinos. These so-called geoneutrinos can provide valuable information on the Earth's interior. A first indication for geoneutrinos was found by the KamLAND experiment in 2005, updated results have been presented by KamLAND,<ref name=Gando-Gando-Hanakago-Ikeda-etal-2013-KamLAND/> and [[Borexino]].<ref name=Agostini-Appel-Bellini-Benziger-etal-2015/> The main background in the geoneutrino measurements are the antineutrinos coming from reactors.

[[File:Proton proton cycle.svg|upright=1.5|thumb|Solar neutrinos ([[proton–proton chain]]) in the Standard Solar Model]]

 

Atmospheric neutrinos result from the interaction of cosmic rays with atomic nuclei in the [[Earth's atmosphere]], creating showers of particles, many of which are unstable and produce neutrinos when they decay. A collaboration of particle physicists from [[Tata Institute of Fundamental Research]] (India), [[Osaka City University]] (Japan) and [[Durham University]] (UK) recorded the first cosmic ray neutrino interaction in an underground laboratory in [[Kolar Gold Fields]] in India in 1965.<ref name=Krishnswmy-Menon-Narasmhn-etal-1971/>

 

{{main|Solar neutrino}}

Solar neutrinos originate from the [[nuclear fusion]] powering the [[Sun]] and other stars.

The Sun sends enormous numbers of neutrinos in all directions. Each second, about 65 [[1000000000 (number)|billion]] ({{val|6.5|e=10}}) solar neutrinos pass through every square centimeter on the part of the Earth orthogonal to the direction of the Sun.<ref name=Bahcall-Serenelli-Basu-2005/> Since neutrinos are insignificantly absorbed by the mass of the Earth, the surface area on the side of the Earth opposite the Sun receives about the same number of neutrinos as the side facing the Sun.

 

{{See also|Supernova neutrinos|SuperNova Early Warning System|Diffuse supernova neutrino background}}

 

 

For an average supernova, approximately {{10^|57}} (an [[octodecillion]]) neutrinos are released, but the actual number detected at a terrestrial detector <math>N</math> will be far smaller, at the level of

<math display="block">N \sim 10^4 \left(\frac{M}{25 \,\mathsf{kton}}\right) \left(\frac{10 \,\mathsf{kpc}}{d}\right)^2,</math>

where <math>M</math> is the mass of the detector (with e.g. [[Super Kamiokande]] having a mass of 50&nbsp;kton) and <math>d</math> is the distance to the supernova.<ref name=Beacom-Vogel-1999-ν-loc-SN/>

Hence in practice it will only be possible to detect neutrino bursts from supernovae within or nearby the [[Milky Way]] (our own galaxy). In addition to the detection of neutrinos from individual supernovae, it should also be possible to detect the [[diffuse supernova neutrino background]], which originates from all supernovae in the Universe.<ref name=Beacom-2010-diffu-SN-ν/>

 

The energy of supernova neutrinos ranges from a few to several tens of MeV. The sites where [[cosmic rays]] are accelerated are expected to produce neutrinos that are at least one million times more energetic, produced from turbulent gaseous environments left over by supernova explosions: [[Supernova remnant]]s. The origin of the cosmic rays was attributed to supernovas by [[Walter Baade|Baade]] and [[Fritz Zwicky|Zwicky]]; this hypothesis was refined by [[Vitaly L. Ginzburg|Ginzburg]] and [[Sergei I. Syrovatsky|Syrovatsky]] who attributed the origin to supernova remnants, and supported their claim by the crucial remark, that the cosmic ray losses of the Milky Way is compensated, if the efficiency of acceleration in supernova remnants is about 10&nbsp;percent. [[Vitaly L. Ginzburg|Ginzburg]] and Syrovatskii's hypothesis is supported by the specific mechanism of "shock wave acceleration" happening in supernova remnants, which is consistent with the original theoretical picture drawn by [[Enrico Fermi]], and is receiving support from observational data. The very high-energy neutrinos are still to be seen, but this branch of neutrino astronomy is just in its infancy. The main existing or forthcoming experiments that aim at observing very-high-energy neutrinos from our galaxy are [[Baikal Deep Underwater Neutrino Telescope|Baikal]], [[Antarctic Muon And Neutrino Detector Array|AMANDA]], [[IceCube]], [[ANTARES (telescope)|ANTARES]], [[KM3NeT|NEMO]] and [[Nestor Project|Nestor]]. Related information is provided by [[ultra-high-energy gamma ray|very-high-energy gamma ray]] observatories, such as [[VERITAS]], [[High Energy Stereoscopic System|HESS]] and [[MAGIC (telescope)|MAGIC]]. Indeed, the collisions of cosmic rays are supposed to produce charged pions, whose decay give the neutrinos, neutral pions, and gamma rays the environment of a supernova remnant, which is transparent to both types of radiation.

 

Still-higher-energy neutrinos, resulting from the interactions of extragalactic cosmic rays, could be observed with the [[Pierre Auger Observatory]] or with the dedicated experiment named [[Antarctic Impulsive Transient Antenna|ANITA]].

 

{{Main|Cosmic neutrino background}}

It is thought that, just like the cosmic microwave background radiation leftover from the Big Bang, there is a background of low-energy neutrinos in our Universe. In the 1980s it was proposed that these may be the explanation for the [[dark matter]] thought to exist in the universe. Neutrinos have one important advantage over most other dark matter candidates: They are known to exist. This idea also has serious problems.

From cosmological arguments, relic background neutrinos are estimated to have density of 56&nbsp;of&nbsp;each type per cubic centimeter and temperature {{val|1.9|u=K}} ({{val|1.7|e=-4|u=eV}}) if they are massless, much colder if their mass exceeds {{val|0.001|u=eV/c2}}. Although their density is quite high, they have not yet been observed in the laboratory, as their energy is below thresholds of most detection methods, and due to extremely low neutrino interaction cross-sections at sub-eV energies. In contrast, [[boron-8]] solar neutrinos—which are emitted with a higher energy—have been detected definitively despite having a space density that is lower than that of relic neutrinos by some six [[orders of magnitude]].

 

{{Main|Neutrino detector}}

 

 

From known {{SubatomicParticle|Beta+}} decay:

{{block indent|Energy {{math| + {{SubatomicParticle|Proton}} → {{SubatomicParticle|Neutron}} + {{SubatomicParticle|Positron}} + {{SubatomicParticle|Electron neutrino}} }}}}

 

Since then, various detection methods have been used. [[Super Kamiokande]] is a large volume of water surrounded by [[photomultiplier tube]]s that watch for the [[Cherenkov radiation]] emitted when an incoming neutrino creates an electron or muon in the water. The Sudbury Neutrino Observatory is similar, but used [[heavy water]] as the detecting medium, which uses the same effects, but also allows the additional reaction any-flavor neutrino photo-dissociation of deuterium, resulting in a free neutron which is then detected from gamma radiation after chlorine-capture. Other detectors have consisted of large volumes of [[chlorine]] or [[gallium]] which are periodically checked for excesses of [[argon]] or [[germanium]], respectively, which are created by electron-neutrinos interacting with the original substance. MINOS used a solid plastic [[scintillator]] coupled to photomultiplier tubes, while Borexino uses a liquid [[pseudocumene]] scintillator also watched by photomultiplier tubes and the [[NOνA]] detector uses liquid scintillator watched by [[avalanche photodiode]]s. The [[IceCube Neutrino Observatory]] uses {{val|1|u=km3}} of the [[Antarctic ice sheet]] near the [[south pole]] with photomultiplier tubes distributed throughout the volume.

 

Neutrinos' low mass and neutral charge mean they interact exceedingly weakly with other particles and fields. This feature of weak interaction interests scientists because it means neutrinos can be used to probe environments that other radiation (such as light or radio waves) cannot penetrate.

 

 

Neutrinos are also useful for probing [[Neutrino astronomy|astrophysical]] sources beyond the Solar System because they are the only known particles that are not significantly [[attenuation|attenuated]] by their travel through the interstellar medium. Optical photons can be obscured or diffused by dust, gas, and background radiation. High-energy cosmic rays, in the form of swift protons and atomic nuclei, are unable to travel more than about 100&nbsp;[[megaparsec]]s due to the [[Greisen–Zatsepin–Kuzmin limit]] (GZK cutoff). Neutrinos, in contrast, can travel even greater distances barely attenuated.

In June 2023, astronomers reported using a new technique to detect, for the first time, the release of neutrinos from the [[galactic plane]] of the Milky Way [[galaxy]].<ref name="NYT-20230629">{{cite news |last=Chang |first=Kenneth |title=Neutrinos Build a Ghostly Map of the Milky Way - Astronomers for the first time detected neutrinos that originated within our local galaxy using a new technique. |url=https://www.nytimes.com/2023/06/29/science/neutrinos-milky-way-map.html |work=[[The New York Times]] |date=29 June 2023 |url-status=live |archive-url=https://archive.today/20230629182106/https://www.nytimes.com/2023/06/29/science/neutrinos-milky-way-map.html |archive-date=29 June 2023 |access-date=30 June 2023 }}</ref><ref name="SCI-20230629">{{cite journal |author=IceCube Collaboration |title=Observation of high-energy neutrinos from the Galactic plane |url=https://www.science.org/doi/10.1126/science.adc9818 |date=29 June 2023 |journal=[[Science (journal)|Science]] |volume=380 |issue=6652 |pages=1338–1343 |doi=10.1126/science.adc9818 |pmid=37384687 |arxiv=2307.04427 |s2cid=259287623 |url-status=live |archive-url=https://archive.today/20230630042539/https://www.science.org/doi/10.1126/science.adc9818 |archive-date=30 June 2023 |access-date=30 June 2023 }}</ref>

 

* {{anl|List of neutrino experiments}}

* {{anl|Multi-messenger astronomy}}

* {{anl|Pontecorvo–Maki–Nakagawa–Sakata matrix}}

 

{{notelist}}

 

{{reflist|25em|refs=

 

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|arxiv=1203.2847 |s2cid=119237711 <!-- ----- -->

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{{Wiktionary|neutrino}}

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{{particles}}