(Redirected from Neutrino astronomy)
The Sudbury Neutrino Observatory is a 12-meter sphere filled with heavy water surrounded by light detectors located 2000 meters below the ground in Sudbury, Ontario, Canada. Credit: A. B. McDonald (Queen's University) et al., The Sudbury Neutrino Observatory Institute.

The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A. Neutrino astronomy observes astronomical objects with neutrino detectors in special observatories.

## Universals

The "neutrino fluxes [may be] predicted by such scenarios [as the standard model or grand unification] if consistency with the observed cosmic ray flux and the universal γ-ray background at 1 − 10 GeV is required. Flux levels detectable by proposed km3 scale neutrino observatories are allowed by these constraints. Bounds on or detection of a neutrino flux above ~ 1 EeV would allow neutrino astronomy to probe grand unification scale physics."[1]

"The shapes of the [ultra-high energy] UHE nucleon and γ-ray spectra predicted within ["top-down"] TD models are “universal” in the sense that they depend only on the physics of [a supermassive elementary "X" particle associated with some grand unified theory (GUT)] X particle decay."[1]

"In contrast to the universality of UHE spectral shapes, the predicted γ-ray flux below ∼ 1014 eV (the threshold for pair production of photons on the [cosmic microwave background] CMB) and the predicted neutrino flux depend on the total energy release integrated over redshift and thus on the specific TD model."[1]

"Observational data on the universal γ-ray background in the 1 − 10 GeV region [27], to which the generic cascade spectrum would contribute directly, turn out to provide an important constraint. Since the UHE γ-ray flux is especially sensitive to certain astrophysical parameters such as the extragalactic magnetic field (EGMF), a reliable calculation of the predicted spectral shapes requires numerical methods."[1]

"The calculations take into account all the relevant interactions with the (redshift dependent) universal low energy photon background in the radio, microwave and optical/infrared regime."[1]

"Above ≃ 100 EeV the corresponding fluxes would dominate all present model predictions for AGN neutrino fluxes [14] as well as the flux of “cosmogenic” neutrinos produced by interactions of UHE [cosmic rays] CRs with the universal photon background [37,38,31]."[1]

The "constraint imposed by requiring that TD scenarios do not overproduce the measured universal γ-ray background at 1 − 10 GeV implies an upper limit on these neutrino fluxes which only depends on the ratio r of energy injected into the neutrino versus [electromagnetic] EM channel, and not on any specific TD scenario or even a possible connection to UHE CRs."[1]

## Astronomy

"[O]ccultation by our planet's core-mantle structure can help constrain the locations of extragalactic neutrino sources."[2]

Instead of emitting positrons and neutrinos, some proton-rich nuclides were found to capture their own atomic electrons (electron capture), and emit only a neutrino (and usually also a gamma ray). Each of these types of decay involves the capture or emission of nuclear electrons or positrons, and acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons (neutrons plus protons).

## Leptogenesis

"In realistic unified models involving so-called SO(10)-inspired patterns of Dirac and heavy right-handed (RH) neutrino masses, the lightest right-handed neutrino N1 is too light to yield successful thermal leptogenesis, barring highly fine tuned solutions, while the second heaviest right-handed neutrino N2 is typically in the correct mass range."[3]

Flavour "coupling effects in the Boltzmann equations may be crucial to the success of such N2 dominated leptogenesis, by helping to ensure that the flavour asymmetries produced at the N2 scale survive N1 washout."[3]

The "only relevant asymmetry is that one produced at the N2 scale in the tauon flavour".[3]

"This implies that, at least at lower order, the observed asymmetry can only be produced in the tauon flavour".[3]

The "asymmetry is mainly produced by the next-to-lightest RH neutrinos in the tauon flavour but this asymmetry is fully washed-out by the lightest RH neutrinos since the condition K ≲􏰗 1 is not compatible with the measured values of the mixing parameters."[3]

One "has also to consider that part of the asymmetry in the tauon flavour is transferred to the electron and muon flavours by flavour coupling effects due primarily to the fact that N2-decays produce in addition to an asymmetry in the tauon lepton doublets also an (hyper charge) asymmetry in the Higgs bosons. This Higgs asymmetry unavoidably induces, through the inverse decays, also an asymmetry in the lepton doublets that at the production are a coherent admixture of electron and muon components. Therefore, in this case, inverse decays actually produce an asymmetry instead of wash it out as in a traditional picture."[3]

"It should be noticed how the source of the electron and muon asymmetries is in any case the tauon asymmetry, but part of this induces a muon and an electron asymmetry thanks to flavour coupling."[3]

"The A to Z model can not only provide a satisfactory fit to all parameters in the leptonic mixing matrix but can also reproduce the correct value of the matter-antimatter asymmetry with N2-dominated leptogenesis. In this respect it is crucial to account for flavour coupling effects due to the redistribution of the asymmetry in particles that do not participate directly to the generation of the asymmetry, in primis the Higgs asymmetry. In particular a “flavour swap” scenario is realised whereby the asymmetry generated in the tauon flavour emerges as a surviving asymmetry dominantly in the muon flavour. The solution works even in the simplest case where the neutrino Dirac mass matrix is equal to the up quark mass matrix."[3]

"The muon and the tauon are unstable and after a while they decay into electrons."[4]

## Neutrinos

In this photograph is recorded the first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph. Credit: Argonne National Laboratory.

A neutrino is an electrically neutral, weakly interacting elementary subatomic particle[5] with half-integer spin. ... Neutrinos do not carry electric charge, which means that they are not affected by the electromagnetic forces that act on charged particles such as electrons and protons. Neutrinos are affected only by the weak sub-atomic force, of much shorter range than electromagnetism, and gravity, which is relatively weak on the subatomic scale. They are therefore able to travel great distances through matter without being affected by it.

"If neutrinos have negligible rest mass, the present density expected for relic neutrinos from the big bang is nν = 110 (Tγ/2.7 K)3 cm–3 for each two-component species. This is of order the photon density nγ, differing just by a factor 3/11 (i.e. a factor 3/4 because neutrinos are fermions rather than bosons, multiplied by 4/11, the factor by which the neutrinos are diluted when e+–e annihilation boosts the photon density). This conclusion holds for non-zero masses, provided that mvc2 is far below the thermal energy (~ 5 MeV) at which neutrinos decoupled from other species and that the neutrinos are stable for the Hubble time. Comparison with the baryon density, related to Ω via nb = 1.5 x 10–5 Ωb h2 cm–3, shows that neutrinos outnumber baryons by such a big factor that they can be dynamically dominant over baryons even if their masses are only a few electron volts. In fact, a single species of neutrino would yield a contribution to Ω of Ωv = 0.01 h–2 (mv)eV, so if h = 0.5, only 25 eV is sufficient to provide the critical density."[6]

"Neutrinos of nonzero mass would be dynamically important not only for the expanding universe as a whole but also for large bound systems such as clusters of galaxies. This is because they would now be moving slowly: if the universe had cooled homogeneously, primordial neutrinos would now be moving at around 200 (mv)-1eV km s–1. They would be influenced even by the weak (~ 10–5 c2) gravitational potential fluctuations of galaxies and clusters. If the three (or more) types of neutrinos have different masses, then the heaviest will obviously be gravitationally dominant, since the numbers of each species should be the same."[6]

The "lightest of the three neutrinos has a mass of at most 0.086 electronvolts, meaning it is at least 6 million times lighter than an electron."[7]

## Neutrino astrophysics

"The observations of solar and supernova neutrinos open up a new area of science: neutrino astrophysics. [...] solar neutrinos provide a beam of elementary particles that can be used to investigate fundamental physics, in particular to study intrinsic neutrino properties."[8]

"Neutrino astrophysics offers new perspectives on the Universe investigation: high energy neutrinos, produced by the most energetic phenomena in our Galaxy and in the Universe, carry complementary (if not exclusive) information about the cosmos with respect to photons. While the small interaction cross section of neutrinos allows them to come from the core of astrophysical objects, it is also a drawback, as their detection requires a large target mass. This is why it is convenient put huge cosmic neutrino detectors in natural locations, like deep underwater or under-ice sites."[9]

## Planetary sciences

"Astrophysical sources of very high energy neutrinos may offer a novel means of imaging the Earth's internal structure."[2]

"The Kamioka liquid scintillator anti-neutrino detector (KamLAND) is a low-energy and low-background neutrino detector which could be a useful probe for determining the U and Th abundances of the Earth."[10]

## Colors

Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo[11] whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates. Neutrino oscillation is of theoretical and experimental interest since observation of the phenomenon implies that the neutrino has a non-zero mass.

A great deal of evidence for neutrino oscillation has been collected from many sources, over a wide range of neutrino energies and with many different detector technologies.[12]

## Minerals

"LOREX, the acronym of LORandite EXperiment, is the only long-time solar neutrino experiment still actively pursued. It addresses the long-time detection of the solar neutrino flux with the thallium-bearing mineral lorandite, TlAsS2 at the mine of Allchar"[13]

## Theoretical neutrino astronomy

This diagram contains the neutrino flux predictions for the 2005 Bahcall and Serenelli Standard Solar Model. Credit: John N. Bahcall, Aldo M. Serenelli, and Sarbani Basu.

Def. an "elementary particle that is classified as a lepton, and has an extremely small but nonzero mass and no electric charge"[14] is called a neutrino.

Def. the "detection and study of neutrinos, in order to investigate astronomical objects and the universe"[15] is called neutrino astronomy.

At right is the predicted solar neutrino spectrum.

"The [neutrino] line fluxes (pep and 7Be) are given in number per cm2 per second. The spectra from the pp chain are drawn with solid lines; the CNO spectra are drawn with dotted lines."[8]

The lower "energy thresholds for the ongoing neutrino experiments" are about 0.2 MeV for Gallium, ~0.82 MeV for Cl, and ~7.5 MeV for Kamiokande.[8]

The huge number of neutrinos [a neutron star] emits carries away so much energy that the temperature falls within a few years [after formation] to around 106 kelvin.[16] Even at 1 million kelvin, most of the light generated by a neutron star is in X-rays. In visible light, neutron stars probably radiate approximately the same energy in all parts of visible spectrum, and therefore appear white.

## Entities

"For three quarters of a century, neutrinos have proven the most ghostly of all the quantum entities that make up the universe."[17]

## Sources

Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions, or when cosmic rays hit atoms.

## Objects

Since many neutrinos [are assumed to] come from stellar cores and supernovae, they are released at great temperature/energy. As neutrinos do not interact with matter electromagnetically, they are by definition dark matter.

"Other possible ‘escape clauses’ [to Ωbh2) ≲ 0.1 but not with Ωbh2 = 1 (for ≥ 3 species of neutrinos)] can be invoked—for instance, there might be large-amplitude inhomogeneities in the initial baryon distribution, such that all the baryonic material we can now sample comes from underdense regions, the overdense regions having turned into dark population III objects (Rees 1983)."[6]

## Strong forces

"When two particles are very close, the mutual screening [gives] rise to a short-range strong force which is of the right strength to hold protons and neutrons within the atomic nuclei. [...] The same process originates also a short-range "weak" force on the electron [of the simple deuterium nucleus] closely orbiting a proton, giving rise to the neutron structure which undergoes β- decay."[18]

## Electromagnetics

"Charged-current charged pion production (CC þ) is a process in which a neutrino interacts with an atomic nucleus and produces a muon, a charged pion, and recoiling nuclear fragments."[19]

## Weak forces

As part of the Mikheyev–Smirnov–Wolfenstein effect, The presence of electrons in matter affects neutrino propagation due to charged current coherent forward scattering of the electron neutrinos (i.e., weak interaction). The coherent forward scattering is analogous to the electromagnetic process leading to the refractive index of light in a medium. With antineutrinos, the effective charge that the weak interaction couples to (called weak isospin) has an opposite sign.

"The observation of a neutrino burst within 3 h of the associated optical burst from supernova 1987A in the Large Magellanic Cloud provides a new test of the weak equivalence principle, by demonstrating that neutrinos and photons follow the same trajectories in the gravitational field of the galaxy."[20]

## Continua

In the solar neutrino spectrum predicted by the standard solar model, "The neutrino fluxes from the continuum sources (like pp and 8Be) are given in the units of number per cm2 per second per MeV at one astronomical unit."[8]

## Emissions

There is a "tight overlapping of the MeV photon flow [prompt MeV γ-ray emission] with the shocked regions [containing GeV photons produced in the shocks] [from supernovae ...] These high energy photons are absorbed by the MeV photon flow and generate relativistic e± pairs. [...] Overlapping also influence neutrino emission. Besides the [3 x] 1015 ~ [3 x] 1017 eV neutrino emission [from photomeson interaction] powered by the interaction of the shock accelerated protons with the synchrotron photons [...] there comes another 1014 neutrino emission component powered by protons interacting with the MeV photon flow."[21]

## Absorptions

The "intergalactic medium (IGM) may be ionized by photons emitted from a cosmological distribution of massive neutrinos."[22]

"The absence of absorption troughs in quasar spectra due to atomic hydrogen and helium, and the possible presence of a trough due to singly ionized helium, would then imply that the neutrino mass lies between 50 and 110 eV."[22]

A "calculated lifetime depends critically on whether a mechanism called GIM suppression is operating (de Rujula & Glashow 1980). [...] However, if GIM suppression does not operate (e.g. if there are four neutrino flavours) [... and] the CIV observed by IUE high up in our galactic halo owes its ionization to photons from decaying neutrinos which dominant the halo [...] 96 eV ≤ mν ≤ 110 eV τ ~ 1027 s. These latter ideas might be tested by searching above the atmosphere for a faint narrow emission line (Δλ ~ 10-3λ) at high galactic latitudes with a photon energy lying between 47.9 and ~ 55 eV."[22]

## Bands

Flux (Φ) of 8B solar neutrinos which are μ or τ flavor vs the flux of electron neutrinos (Φe) deduced from the three neutrino reactions in the Sudbury Neutrino Observatory (SNO). Credit: Ahmad et al..

"Using the neutral current [NC], elastic scattering [ES], and charged current [CC] reactions and assuming the standard 8B shape, the νe component of the 8B solar flux is Φe = 1.76±0.05 ([statistical uncertainty] stat.)±0.09 ([systematic uncertainty]syst.) x 106 cm-2s-1 for a kinetic threshold of 5 MeV. The non-νe component is Φµτ = 3.41±0.45 (stat.) +0.48 or -0.45 (syst.) x 106 cm-2s-1, 5.3σ greater than zero, providing strong evidence for solar νe flavor transformation."[23]

"The Sudbury Neutrino Observatory (SNO) detects 8B solar neutrinos through the reactions:"[23]

${\displaystyle \nu _{e}+d\rightarrow p^{+}+p^{+}+e^{-}(CC),}$
${\displaystyle \nu _{x}+d\rightarrow p^{+}+n^{0}+\nu _{x}(NC),}$
${\displaystyle \nu _{x}+e^{-}\rightarrow \nu _{x}+e^{-}(ES).}$

"The charged current reaction (CC) is sensitive exclusively to electron-type neutrinos, while the neutral current reaction (NC) is equally sensitive to all active neutrino flavors (x = e, μ, τ). The elastic scattering reaction (ES) is sensitive to all flavors as well, but with reduced sensitivity to νμ and ντ."[23]

"The bands intersect [in the figure at right] at the fit values for Φe and Φµτ, indicating that the combined flux results are consistent with neutrino flavor transformation assuming no distortion in the 8B neutrino energy spectrum."[23]

## Backgrounds

The cosmic neutrino background (CNB) is the background particle radiation composed of neutrinos as a relic of the big bang which decoupled from matter when the universe was 2 seconds old.

## Meteors

"The isotope 92Nb decays to 92Zr with a half-life of 3.47 × 107 yr. Although this isotope does not exist in the current solar system, initial abundance ratios for 92Nb/93Nb at the time of solar system formation have been measured in primitive meteorites."[24]

A "novel origin for 92Nb may be via neutrino-induced reactions in core-collapse supernovae (ν-process)."[24]

The "observed ratio of 92Nb/93Nb ~ 10-5 can be explained by the ν-process.[24]

## Subatomics

Based on interactions between cosmic rays and the photons of the cosmic microwave background radiation (CMB), cosmic rays with energies over the threshold energy of some 5 x 1019 eV, a theoretical upper limit: the Greisen–Zatsepin–Kuzmin limit (GZK limit), interact with cosmic microwave background photons ${\displaystyle \gamma _{\rm {CMB}}}$ to produce pions via the ${\displaystyle \Delta }$ resonance,

${\displaystyle \gamma _{\rm {CMB}}+p\rightarrow \Delta ^{+}\rightarrow p+\pi ^{0},}$

or

${\displaystyle \gamma _{\rm {CMB}}+p\rightarrow \Delta ^{+}\rightarrow n+\pi ^{+}.}$

Pions produced in this manner proceed to decay in the standard pion channels—ultimately to photons for neutral pions, and photons, positrons, and various neutrinos for positive pions. Neutrons decay also to similar products, so that ultimately the energy of any cosmic ray proton is drained off by production of high energy photons plus (in some cases) high energy electron/positron pairs and neutrino pairs.

## Cosmic rays

Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions, or when cosmic rays hit atoms.

Cosmic "ray neutrinos of local origin are also the background for neutrino astronomy."[25]

## Neutrals

"Neutral current single π0 production induced by neutrinos with a mean energy of 1.3GeV is measured at a 1000 ton water Cherenkov detector as a near detector of the K2K long baseline neutrino experiment."[26]

"The single π0 production rate by atmospheric neutrinos could be usable to distinguish between the νµ ↔ ντ and νµ ↔ νs oscillation hypotheses. The NC rate is attenuated in the case of transitions of νµ’s into sterile neutrinos, while it does not change in the νµ ↔ ντ scenario."[26]

"Atmospheric neutrinos can interact with the detector producing also hadrons. The most probable of these reactions is the single pion production [20][21]:"[27]

${\displaystyle \nu _{\mu }+p\rightarrow \mu ^{-}+\pi ^{+}+p^{'}.}$

"There is also a small loss due to inelastic hadronic interactions of the decay particles before they are stopped."[27]

The "optical properties of mixtures of PXE [phenyl-o-xylylethane] and derivatives of mineral oils are under investigation [3]."[27]

"Neutrino detection includes four remarkable reactions:"[28]

1. Muon production νμ + N → μ + all gives an excellent tool to search for the discrete sources, since directions of UHE muon and neutrino coincide.
2. Resonant production of W-boson, νe + e → W → hadrons results in production of monoenergetic showers with energy E0 = ${\displaystyle m_{W}^{2}}$/2me = 6.3 × 106 GeV. This reaction has a large cross-section.
3. Tau production in a detector, ντ + N → τ + hadrons, is characterised by time sequence of three signals: a shower from prompt hadrons, the Cherenkov light from τ and hadron shower from τ-decay. SuperGZK ντ are absorbed less in the Earth due to regeneration: absorbed ντ is converted into τ, which decays producing ντ again.
4. Z-bursts provide a signal from the space, caused by the resonant Z0 production on DM neutrinos, ν + νDM → Z0 → hadrons. The energy of the detected neutrino must be tremendous: E0 = ${\displaystyle {\frac {m_{Z}^{2}}{2m_{\nu }}}=1.7\times 10^{13}{\frac {0.23eV}{m_{\nu }}}GeV.}$

Non-accelerator neutrino sources "include objects with annihilation of DM (the Sun, Earth, cores of the galaxies), objects with the decays of superheavy DM particles (galactic halos) and topological defects. In the last two cases neutrinos are produced in the decays of superheavy particles with the masses up to MGUT ∼ 1016 GeV. A particle decays to virtual particles, partons, which are cascading due to QCD interaction, and at the confinement radius cascade partons are converted to hadrons, most of which are pions. Neutrinos are produced in pion decays with spectrum which can be approximately described at highest energies as dE/E2.[28]

## Neutrons

Around EeV (1018 eV) energies of ultra high energy neutron astronomy there may be associated ultra high energy neutrons “observed in anisotropic clustering ... because of the relativistic neutrons boosted lifetime.”[29] “[A]t En = 1020 eV, [these neutrons] are flying a Mpc, with their directional arrival (or late decayed proton arrival) ... more on-line toward the source.”[29] Although “neutron (and anti-neutron) life-lengths (while being marginal or meaningless at tens of Mpcs, the growth of their half-lives with energy may naturally explain an associated, showering neutrino halo.”[29]

## Protons

Solar neutrinos are shown for the proton-proton chain in the Standard Solar Model. Credit: Dorottya Szam.

The following fusion reaction produces neutrinos and accompanying gamma-rays of the energy indicated:

${\displaystyle \mathrm {_{1}^{1}H} +\mathrm {_{1}^{1}H} \rightarrow \mathrm {_{1}^{2}D} +e^{+}+\nu _{e}+\gamma (0.42MeV).}$

Observation of gamma rays of this energy likely indicate this reaction is occurring nearby.

In the Cowan–Reines neutrino experiment, antineutrinos created in a nuclear reactor by beta decay reacted with protons producing neutrons and positrons:

ν
e
+ p+
n0
+ e+

The positron quickly finds an electron, and they annihilate each other. The two resulting gamma rays (γ) [511 keV each] 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.

"It is fair to note, however, that almost all theories which invoke non-baryonic matter require some level of coincidence in order that the luminous and unseen mass contribute comparable densities (to within one or two powers often). For instance, in a neutrino-dominated universe, (mv/mproton) must be within a factor ~ 10 of nb/nγ. The only model that seems to evade this requirement is Witten’s (1984) idea that the quark-hadron phase transition may leave comparable amounts of material in ‘ordinary’ baryons and in ‘nuggets’ of exotic matter."[6]

## Electrons

A "PeV energy photon cannot deliver information from a source at the edge of our own galaxy because it will annihilate into an electron [positron] pair in an encounter with a 2.7 Kelvin microwave photon before reaching our telescope."[30]

"In general, energetic photons above a threshold E given by

${\displaystyle 4E\epsilon \sim (2m_{e})^{2},}$

where E and ε are the energy of the high-energy and background photon, respectively. [This] implies that TeV-photons are absorbed on infrared light, PeV photons on the cosmic microwave background and EeV photons on radio-waves".[30]

"Each [optical module] OM contains a 10 inch [photo-multiplier tube] PMT that detects individual photons of Cerenkov light generated in the optically clear ice by muons and electrons moving with velocities near the speed of light."[30]

"Radio Cerenkov experiments detect the Giga-Hertz pulse radiated by shower electrons produced in the interaction of neutrinos in ice."[30]

"Above a threshold of ≃ 1PeV, the large number of low energy(≃ MeV ) photons in a shower will produce an excess of electrons over positrons by removing electrons from atoms by Compton scattering. These are the sources of coherent radiation at radio frequencies, i.e. above ∼ 100MHz."[30]

## Positrons

This graph shows positron emissions, among others, from nuclear transmutation. Credit: .
Naturally occurring electron-positron annihilation is a result of beta plus decay. Credit: .

"If the proton and neutron are part of an atomic nucleus, these decay processes transmute one chemical element into another. For example:

${\displaystyle A_{Z}N\rightarrow ~_{Z-1}^{~~~A}N'+e^{+}+\nu _{e},}$

where A = 22, Z = 11, N = Na, Z-1 = 10, and N' = Ne.

Beta decay does not change the number of nucleons, A, in the nucleus but changes only its charge, Z. Thus the set of all nuclides with the same A can be introduced; these isobaric nuclides may turn into each other via beta decay. Among them, several nuclides (at least one) are beta stable, because they present local minima of the mass excess: if such a nucleus has (A, Z) numbers, the neighbour nuclei (A, Z−1) and (A, Z+1) have higher mass excess and can beta decay into (A, Z), but not vice versa. For all odd mass numbers A the global minimum is also the unique local minimum. For even A, there are up to three different beta-stable isobars experimentally known. There are about 355 known beta-decay stable nuclides total.

In β+
decay, or "positron emission", the weak interaction converts a nucleus into its next-lower neighbor on the periodic table while emitting an positron (e+
) and an electron neutrino (ν
e
):

${\displaystyle _{Z}^{A}N\rightarrow ~_{Z-1}^{~~~A}N'+e^{+}+\nu _{e}.}$

β+
decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton. β+
decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.

Positron emission' or beta plus decay (β+ decay) is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino.

Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-121. As an example, the following equation describes the beta plus decay of carbon-11 to boron-11, emitting a positron and a neutrino:

${\displaystyle _{6}^{11}C\rightarrow ~_{5}^{11}B+e^{+}+\nu _{e}+\gamma {(0.96MeV)}.}$

The figure at right shows a positron (e+) emitted from an atomic nucleus together with a neutrino (v). Subsequently, the positron moves randomly through the surrounding matter where it hits several different electrons (e-) until it finally loses enough energy that it interacts with a single electron. This process is called an "annihilation" and results in two diametrically emitted photons with a typical energy of 511 keV each. Under normal circumstances the photons are not emitted exactly diametrically (180 degrees). This is due to the remaining energy of the positron having conservation of momentum.

At energies near and beyond the mass of the carriers of the weak force, the W and Z bosons, the strength of the weak force becomes comparable with electromagnetism.[31] It becomes much easier to produce particles such as neutrinos that interact only weakly.

## Muons

"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."[32]

Muon decay produces three particles, an electron plus two neutrinos of different types.

"The muons created through decays of secondary pions and kaons are fully polarized, which results in electron/positron decay asymmetry, which in turn causes a difference in their production spectra."[33]

## Gamma rays

"The important conclusion is that, independently of the specific blueprint of the source, it takes a kilometer-scale neutrino observatory to detect the neutrino beam associated with the highest energy cosmic rays and gamma rays."[30]

"As with supernovae, [gamma-ray burst] GRB are expected to radiate the vast majority of their initial energy as thermal [MeV] neutrinos."[30]

"Protons [shocked protons: TeV - EeV neutrinos] accelerated in GRB can interact with fireball gamma rays and produce pions that decay into neutrinos."[30]

"In a GRB fireball, neutrons can decouple from protons in the expanding fireball. If their relative velocity is sufficiently high, their interactions will be the source of pions and, therefore, neutrinos [GeV]. Typical energies of the neutrinos produced are much lower than those resulting from interactions with gamma rays."[30]

## X-rays

Some "of the possible sources of the ultra-high energy cosmic rays, such as very young supernova remnants and X-ray binaries, are associated with relatively dense concentrations of matter and would therefore be likely point sources of secondary photons and neutrinos."[25]

## Ultraviolets

"Massive neutrinos are expected to decay into lighter neutrinos and uv photons, with lifetimes long on the Hubble scale."[34]

## Opticals

"The arrival times of the Cerenkov photons in 6 optical sensors determine the direction of the muon track."[30]

"The optical requirements on the detector medium are severe. A large absorption length is needed because it determines the required spacing of the optical sensors and, to a significant extent, the cost of the detector. A long scattering length is needed to preserve the geometry of the Cerenkov pattern. Nature has been kind and offered ice and water as natural Cerenkov media. Their optical properties are, in fact, complementary. Water and ice have similar attenuation length, with the roles of scattering and absorption reversed. Optics seems, at present, to drive the evolution of ice and water detectors in predictable directions: towards very large telescope area in ice exploiting the long absorption length, and towards lower threshold and good muon track reconstruction in water exploiting the long scattering length."[30]

"The Baikal experiment represents a proof of concept for future deep ocean projects that have the advantage of larger depth and optically superior water."[30]

"With the attenuation length peaking at 55m near 470 nm, the site is optically similar to that of the best deep water sites investigated for neutrino astronomy."[30]

"Astronomy, whether in the optical or in any other wave-band, thrives on a diversity of complementary instruments, not on “a single best instrument”."[30]

## Visuals

"With an optical depth of order ∼ 1015, photons are trapped in the fireball. This results in the highly relativistic expansion of the fireball powered by radiation pressure [168, 177]. The fireball will expand with increasing velocity until it becomes transparent and the radiation is released. This results in the visual display of the GRB."[30]

## Violets

"At present all the LEDs used [in the ANTARES neutrino telescope] emit light in the blue at 470nm with a FWHM of 15nm, however, the design is flexible enough to use violet or near-ultraviolet LEDs if there is sufficient interest in water transmission monitoring at these wavelengths and if the individual LED prices permit."[35]

## Blues

Supernova SN 1987A is one of the brightest stellar explosions since the invention of the telescope more than 400 years ago.[36] Credit: ESA/Hubble & NASA.

"On February 23.316 UT, 1987, [blue] light and neutrinos from the brightest supernova in 383 years arrived at Earth ... it has been observed ... at all wavelengths from radio through gamma rays, SN 1987A is the only object besides the Sun to have been detected in neutrinos."[37]

At left is an image of supernova SN 1987A, one of the brightest stellar explosions since the invention of the telescope more than 400 years ago.[36]

Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak -69° 202, a blue supergiant.[38] This was an unexpected identification, because at the time a blue supergiant was not considered a possibility for a supernova event in existing models of high mass stellar evolution. Many models of the progenitor have attributed the color to its chemical composition, particularly the low levels of heavy elements, among other factors.[37]

## Reds

"[N]on-standard neutrino losses [may have an] impact on the red giant branch (RGB)".[39]

## Infrareds

"For neutrino masses in the eV regime, such a radiative decay process would contribute to the infrared background."[40]

The "Shapiro geodesic time delay is identical, to this accuracy, for different elementary particles, independent of spin and internal quantum numbers."[20]

"To test the [weak equivalence principle] WEP, however, the issue is not the value of γ but whether it is the same for all species of particles, that is, whether, for example, the same time delay would be measured if neutrino radar rather than photon radar were used."[20]

"The neutrino energy is, however, above the threshold for EeV telescopes using acoustic, radio or horizontal air shower detection techniques. This mechanism may represent an opportunity for detectors with very high threshold, but also large effective area to do GRB physics."[30]

## Superluminals

"Because neutrinos are electrically neutral, conventional Cherenkov radiation of superluminal neutrinos does not arise or is otherwise weakened. However neutrinos do carry electroweak charge and ... may emit Cherenkov-like radiation via weak interactions when traveling at superluminal speeds."[41]

"[S]uperluminal neutrinos may lose energy rapidly via the bremsstrahlung [Cherenkov radiation] of electron-positron pairs ${\displaystyle (\nu \rightarrow \nu +e^{-}+e^{+}).}$"[42]

Assumption:

"muon neutrinos with energies of order tens of GeV travel at superluminal velocity."[42]

For "all cases of superluminal propagation, certain otherwise forbidden processes are kinematically permitted, even in vacuum."[42]

Consider

${\displaystyle \nu _{\mu }\rightarrow {\begin{bmatrix}{\nu _{\mu }+\gamma }&(a)\\{\nu _{\mu }+\nu _{e}+{\overline {\nu }}_{e}}&(b)\\{\nu _{\mu }+e^{+}+e^{-}}&(c)\end{bmatrix}}}$[42]

"These processes cause superluminal neutrinos to lose energy as they propagate and ... process (c) places a severe constraint upon potentially superluminal neutrino velocities. ... Process (c), pair bremsstrahlung, proceeds through the neutral current weak interaction."[42]

"Throughout the shower development, the electrons and positrons which travel faster than the speed of light in the air emit Cherenkov radiation."[43]

"High energy processes such as Compton, Bhabha, and Moller scattering, along with positron annihilation rapidly lead to a ~20% negative charge asymmetry in the electron-photon part of a cascade ... initiated by a ... 100 PeV neutrino"[44].

## Plasma objects

"The exploding [GRB] fireballs original size, R0, is that of the compact progenitor, for instance the black hole created by the collapse of a massive star. As the fireball expands the flow is shocked in ways familiar from the emission of jets by the black holes at the centers of active galaxies or mini-quasars. (A way to visualize the formation of shocks is to imagine that infalling material accumulates and chokes the black hole. At this point a blob of plasma is ejected. Between these ejections the emission is reduced.) The net result is that the expanding fireball is made up of multiple shocks. These are the sites of the acceleration of particles to high-energy and the seeds for the complex millisecond structures observed in individual bursts"[30]

## Gaseous objects

All "these signals are electromagnetic waves and, as such, interact rather strongly with matter. This means that only the information on the thin surface of stellar objects and/or on diffuse gaseous objects can be conveyed by these signals."[45]

## Hydrogens

Cosmic "rays interact with the Earth’s atmosphere [109, 110] and with the hydrogen concentrated in the galactic plane [46, 47, 111, 112, 113] producing high-energy neutrinos."[30]

## Heliums

"The cosmic helium abundance can however be measured with sufficient precision to suggest that the primordial 4He is less than 26 per cent at the 3 σ level (Pagel 1982). This is compatible with Ωbh2) ≲ 0.1 but not with Ωbh2 = 1 (for ≥ 3 species of neutrinos)."[6]

## Lithiums

There is a practical "possibility for utilizing lithium as a solar-neutrino detector".[46]

## Berylliums

The isotopes 7Be, with a half-life of 53 days, and 10Be are both cosmogenic nuclides because they are made on a recent timescale in the solar system by spallation, like 14C. These two radioisotopes of beryllium in the atmosphere track the sun spot cycle and solar activity, since this affects the magnetic field that shields the Earth from cosmic rays. The rate at which the short-lived 7Be is transferred from the air to the ground is controlled in part by the weather. 7Be decay in the sun is one of the sources of solar neutrinos, and the first type ever detected using the Homestake experiment.

## Borons

"Also of importance in this emerging field [of observational neutrino astrophysics] are the observation of solar boron-8 neutrinos and the detection of high-energy point sources."[47]

## Carbons

"In any case a star with a mass equal to or smaller than 7 M cannot have a nonviolent carbon burning phase if the neutrino emission due to “universal Fermi interaction” exists."[48]

## Nitrogens

"The [cosmic-ray] shower can be observed by: i) sampling the electromagnetic and hadronic components when they reach the ground with an array of particle detectors such as scintillators, ii) detecting the fluorescent light emitted by atmospheric nitrogen excited by the passage of the shower particles, iii) detecting the Cerenkov light emitted by the large number of particles at shower maximum, and iv) detecting muons and neutrinos underground."[30]

## Oxygens

"These “atmospheric neutrinos” come from the decay of pions and kaons produced by the collisions of cosmic-ray particles with nitrogen and oxygen in the atmosphere."[49]

## Fluorines

"Measurements of fluorine in the interstellar medium (Federman et al. 2005) show no evidence of F overabundances due to the neutrino process in Type II supernova."[50]

## Neons

The neutrino oscillation signatures are discussed regarding "flavor conversion of neutrinos from core-collapse supernovae that have oxygen-neon-magnesium (ONeMg) cores."[51]

## Galliums

"[R]adiochemical experiments using gallium (the GALLEX experiment6,7 in Italy and the SAGE experiment8,9 in Russia) have detected the copious low energy (below 400 keV) neutrinos that are the primary component of the solar neutrino flux."[8]

## Compounds

The first detection of "solar neutrinos [used] radiochemical techniques and a cleaning fluid (perchloroethylene [C2Cl4]) as a target. [...] After about two months [...] the standard solar model22-24 predicts that only about 54 37Ar atoms are present in the 615 tons of C2Cl4 [...] at extraction [the number observed is] only 17, corresponding to a solar neutrino induced production rate of 0.5 atoms per day, far fewer than the 1.5 atoms per day expected on the basis of the standard model. In terms of the solar neutrino unit, SNU [...] 1 SNU = 10-36 interactions per target atom per second), the observations yield 2.55 ± 0.25 SNU, about one third of the prediction of the standard model."[8]

## Atmospheres

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 the 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.

## Sun

This "neutrino image" of the Sun is produced by using the Super-Kamiokande to detect the neutrinos from nuclear fusion coming from the Sun. Credit: R. Svoboda and K. Gordan (LSU).

Neutrinos are hard to detect. The Super-Kamiokande, or "Super-K" is a large-scale experiment constructed in an unused mine in Japan to detect and study neutrinos. The image at right required 500 days worth of data to produce the "neutrino image" of the Sun. The image is centered on the Sun's position. It covers a 90° x 90° octant of the sky (in right ascension and declination). The higher the brightness of the color, the larger is the neutrino flux.

"The detection of solar neutrinos demonstrates that fusion energy is the basic source of energy received from the sun."[8]

In detecting solar neutrinos, it became clear that the number detected was half or a third than that predicted by models of the solar interior. The problem was solved by revising the properties of neutrinos and understanding the limits of the detection mechanisms - only one third of the forms of neutrinos coming in was being detected and all neutrinos oscillate between the three forms.

The first experiment to detect the effects of neutrino oscillation was Ray Davis's Homestake Experiment in the late 1960s, in which he observed a deficit in the flux of solar neutrinos with respect to the prediction of the Standard Solar Model, using a chlorine-based detector. This gave rise to the Solar neutrino problem. Many subsequent radiochemical and water Cherenkov detectors confirmed the deficit, but neutrino oscillation was not conclusively identified as the source of the deficit until the Sudbury Neutrino Observatory provided clear evidence of neutrino flavor change in 2001. Solar neutrinos have energies below 20 MeV and travel an astronomical unit between the source in the Sun and detector on the Earth. At energies above 5 MeV, solar neutrino oscillation actually takes place in the Sun through a resonance known as the Mikheyev–Smirnov–Wolfenstein effect (MSW) effect, a different process from the vacuum oscillation.

Most neutrinos passing through the Earth emanate from the Sun. About 65 billion (6.5 x 1010) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.[52]

The Mikheyev Smirnov Wolfenstein (MSW) effect is important at the very large electron densities of the Sun where electron neutrinos are produced. The high-energy neutrinos seen, for example, in the Sudbury Neutrino Observatory (SNO) and in Super-Kamiokande, are produced mainly as the higher mass eigenstate in matter ν2m, and remain as such as the density of solar material changes. (When neutrinos go through the MSW resonance the neutrinos have the maximal probability to change their nature, but it happens that this probability is negligibly small—this is sometimes called propagation in the adiabatic regime). Thus, the neutrinos of high energy leaving the sun are in a vacuum propagation eigenstate, ν2, that has a reduced overlap with the electron neutrino νe = ν1 cosθ + ν2 sinθ seen by charged current reactions in the detectors.

For high-energy solar neutrinos the MSW effect is important, and leads to the expectation that Pee = sin²θ, where θ = 34° is the solar mixing angle. This was dramatically confirmed in the Sudbury Neutrino Observatory (SNO), which has resolved the solar neutrino problem. SNO measured the flux of Solar electron neutrinos to be ~34% of the total neutrino flux (the electron neutrino flux measured via the charged current reaction, and the total flux via the neutral current reaction). The SNO results agree well with the expectations.

For the low-energy solar neutrinos, on the other hand, the matter effect is negligible, and the formalism of oscillations in vacuum is valid. The size of the source (i.e. the Solar core) is significantly larger than the oscillation length, therefore, averaging over the oscillation factor, one obtains Pee = 1 − sin²2θ / 2. For the same value of the solar mixing angle (θ = 34°) this corresponds to a survival probability of Pee ≈ 60%. This is consistent with the experimental observations of low energy Solar neutrinos by the Homestake experiment (the first experiment to reveal the solar neutrino problem), followed by GALLEX, the Gallium Neutrino Observatory (GNO), and Soviet–American Gallium Experiment (SAGE) (collectively, gallium radiochemical experiments), and, more recently, the Borexino experiment. These experiments provided further evidence of the MSW effect.

The transition between the low energy regime (the MSW effect is negligible) and the high energy regime (the oscillation probability is determind by matter effects) lies in the region of about 2 MeV for the Solar neutrinos.

## Chromospheres

"[N]eutrino flux increases noted in Homestake results [coincide] with major solar flares [14]."[53]

"The correlation between a great solar flare and Homestake neutrino enhancement was tested in 1991. Six major flares occurred from May 25 to June 15 including the great June 4 flare associated with a coronal mass ejection and production of the strongest interplanetary shock wave ever recorded (later detected from spacecraft at 34, 35, 48, and 53 AU) [15]. It also caused the largest and most persistent (several months) signal ever detected by terrestrial cosmic ray neutron monitors in 30 years of operation [16]. The Homestake exposure (June 1–7) measured a mean 37Ar production rate of 3.2 ± 1.5 atoms/day (≈19 37Ar atoms produced in 6 days) [13]; about 5 times the rate of ≈ 0.65 day −1 for the preceding and following runs, > 6 times the long term mean of ≈ 0.5 day−1 and > 2 1/2 times the highest rates recorded in ∼ 25 operating years."[53]

## Coronal clouds

The highest flux of solar neutrinos come directly from the proton-proton interaction, and have a low energy, up to 400 keV. There are also several other significant production mechanisms, with energies up to 18 MeV.[54]

The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere.[55]

"Neutrinos can be produced by energetic protons accelerated in solar magnetic fields. Such protons produce pions, and therefore muons, hence also neutrinos as a decay product, in the solar atmosphere."[56]

"Energetic protons in the solar corona could explain Figure 2 only if (1) they tap a substantial fraction of the entire energy generated in the corona, (2) the energy generated in the corona is at least 3 times what has been deduced from the observations, (3) the vast majority of energetic protons do not escape the Sun, (4) the proton energy spectrum is unusually hard (p0 = 300 MeV c-1, and (5) the sign of the variation is opposite to what one would predict. As the likelihood of all of these conditions being fulfilled seems extremely small, we do not believe that neutrinos produced by energetic protons in the solar atmosphere contribute significantly to the neutrino capture in the 37Cl experiment."[56]

## Earth

Neutrinos are part of the natural background radiation. In particular, the decay chains of 238U and 232Th isotopes, as well as 40K, 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. KamLAND's main background in the geoneutrino measurement are the antineutrinos coming from reactors.

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 the 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.

## Moon

The "moon, viewed by ground-based radio telescopes, has been used as a target [87]."[30]

## Supernovas

The 1987A supernova remnant is near the center of this image. Credit: First image: Dr. Christopher Burrows, ESA/STScI and NASA; Second image: Hubble Heritage team.

"In the 1980s two early water-Cherenkov experiments were built. The Irvine-Michigan-Brookhaven detector in an Ohio salt mine and the Kamiokande detector in a Japanese zinc mine were tanks containing thousands of tons of purified water, monitored with phototubes. The two detectors launched the field of neutrino astronomy by detecting some 20 low-energy (about 10 MeV) neutrinos from Supernova 1987A—the first supernova since the 17th century that was visible to the naked eye."[57]

The water-based detectors Kamiokande II and IMB detected 11 and 8 antineutrinos of thermal origin,[58] respectively, while the scintillator-based Baksan detector found 5 neutrinos (lepton number = 1) of either thermal or electron-capture origin, in a burst lasting less than 13 seconds.

## Large Magellanic Cloud

"In 1987, astronomers counted 19 neutrinos from an explosion of a star in the nearby Large Magellanic Cloud, 19 out of the billion trillion trillion trillion trillion neutrinos that flew from the supernova."[59]

Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from cosmic rays and other background radiation.[59]

## Astrography

The photograph is of the Fermi National Accelerator Laboratory, Main Ring and Main Injector as seen from the air. Credit: Fermilab, Reidar Hahn.

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

In addition to high energy collider physics, Fermilab is also host to a number of smaller fixed-target and neutrino experiments, such as MiniBooNE (Mini Booster Neutrino Experiment), SciBooNE (SciBar Booster Neutrino Experiment) and MINOS (Main Injector Neutrino Oscillation Search). The MiniBooNE detector is a 40-foot (12 m) diameter sphere which contains 800 tons of mineral oil lined with 1520 individual phototube detectors. An estimated 1 million neutrino events are recorded each year. SciBooNE is the newest neutrino experiment at Fermilab; it sits in the same neutrino beam as MiniBooNE but has fine-grained tracking capabilities. The MINOS experiment uses Fermilab's NuMI (Neutrinos at the Main Injector) beam, which is an intense beam of neutrinos that travels 455 miles (732 km) through the Earth to the Soudan Mine in Minnesota.

## Cosmogony

Consider a universe "dominated by neutrinos and 'cold dark matter'".[6]

"The evidence for unseen mass [...] suggests that the cosmological density parameter Ω is at least 0.1-0.2 [rather than for an] Einstein-de-Sitter 'flat' universe with Ω = 1 [... This] can only be reconciled with the data if the galaxies are more 'clumped' than the overall mass distribution, and are poor tracers of the unseen mass even on scales of several Mpc."[6]

"Particle physicists have other particles ‘in reserve’ which could make a substantial (non-baryonic) contribution to Ω, but which differ from neutrinos in that their freestreaming velocity is negligible, so that small-scale adiabatic perturbations are not phase-mixed away. Such particles can be described as ‘cold dark matter’, in contrast to neutrinos whose free streaming velocity renders them ‘hot’."[6]

"There is no shortage of ‘cold dark matter’ candidate particles—although each of them is highly speculative, to say the least. The motivation for nonetheless considering the hypothesis that the universe is dominated by cold dark matter is that it leads to a cosmogonic scheme that avoids the difficulties of the neutrino-dominated scheme and correctly predicts many of the observed properties of galaxies, including their range of masses, irrespective of the identity of the cold particle (Peebles 1984; Blumenthal et al. 1984)."[6]

## Astromathematics

Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay:[60]

n0
=> p+
+ e
+ ν
e

For the above relation

Notational locations
Weight Oversymbol Exponent
Coefficient Variable Operation
Number Range Index

Starting with the left symbol, Weight is 1 (not mentioned), Oversymbol is not used, Exponent is replaced by Charge, the Coefficient is 1 (not mentioned), the Variable is a letter designation for the subatomic particle of interest (n for neutron), the Operation is actually a relation decays to (=>), Number is the atomic number Z = 0 for a neutron (not mentioned), the Range is not applicable, and no Index is being used. The neutron's decay products are a proton (p), electron (e), and a neutrino (ν), where Index is used to indicate that the neutrino is an electron neutrino and Oversymbol indicates it is actually an antineutrino. The Operation (+) is not mathematical addition, but indicates another decay product.

## Detectors

Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from cosmic rays and other background radiation.[61]

## Antarctic Impulse Transient Antenna

The Antarctic Impulsive Transient Antenna (ANITA) experiment has been designed to study ultra-high-energy (UHE) cosmic neutrinos by detecting the radio pulses emitted by their interacting with the Antarctic ice sheet. This is to be accomplished using an array of 32 radio antennas (cylindrically arranged with an approximate radius of 3m and a height of 5m) suspended from a helium balloon flying at a height of about 35,000 meters.[62] The neutrinos, with energies on the order of 1018 eV, produce radio pulses in the ice because of the Askaryan effect.

## ANTARES

An artist illustration of the Antares neutrino detector and the Nautile. Credit: .

ANTARES is the name of a neutrino detector residing 2.5 km under the Mediterranean Sea off the coast of Toulon, France. It is designed to be used as a directional Neutrino Telescope to locate and observe neutrino flux from cosmic origins in the direction of the Southern Hemisphere of the Earth, a complement to the southern hemisphere neutrino detector IceCube that detects neutrinos from the North.

## Baikal Neutrino Telescope

This diagram shows the arrangement of modules for the Baikal Neutrino Detector in Lake Baikal, Russia. Credit: DESY Zeuthen.

"The underwater neutrino telescope NT200 is located in the Siberian lake Baikal at a depth of approximately 1 km. Deployment and maintenance of the Baikal detector is carried out during the winter months, when the lake is covered with a thick ice sheet. From the ice surface, the optical sensors can easily be lowered into the water underneath. Once deployed, the optical sensors take data over the whole year and the data taken are permanently transmitted to the shore over electrical cables."[63]

"During spring 1993, scientists from Russian institutes and from DESY were the first to install an underwater telescope which took data not only for some hours, but for a whole year. At that time, the detector comprised only three strings carrying 36 optical sensors in total. Since 1998 the Baikal collaboration takes data with the NT200 telescope which consists of 192 optical sensors deployed on eight strings."[63]

## Baksan Neutrino Observatory

The Baksan Neutrino Observatory (BNO) consists of the Baksan Underground Scintillation Telescope, located 300m below the surface,[64] a galliumgermanium neutrino telescope (the SAGE experiment) located 3,500m deep,[64] as well as a number of ground facilities.

## Extreme Universe Space Observatory

This is a computer-generated image of the Extreme Universe Space Observatory (EUSO) as part of the Japanese Experiment Module (JEM) on the International Space Station (ISS). Credit: JEM-EUSO, Angela Olinto.

The Extreme Universe Space Observatory (EUSO) is the first Space mission concept devoted to the investigation of cosmic rays and neutrinos of extreme energy (E > 5×1019
eV
). Using the Earth's atmosphere as a giant detector, the detection is performed by looking at the streak of fluorescence produced when such a particle interacts with the Earth's atmosphere.

## IceCube Neutrino Observatory

This is an architecture diagram of IceCube. Credit: Nasa-verve.

The IceCube Neutrino Observatory (or simply IceCube) is a neutrino telescope constructed at the Amundsen-Scott South Pole Station in Antarctica.[1] Similar to its predecessor, the Antarctic Muon And Neutrino Detector Array (AMANDA), IceCube contains thousands of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT)[65] and a single board data acquisition computer which sends digital data to the counting house on the surface above the array.[66] IceCube was completed on 18 December, 2010, New Zealand time.[67]

## Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory detector was designed to detect solar neutrinos through their interactions with a large tank of heavy water. The detector turned on in May 1999, and was turned off on 28 November 2006.

The experiment observed the light produced by relativistic electrons in the water created by neutrino interactions. As relativistic electrons travel through a medium, they lose energy producing a cone of blue light through the Cerenkov effect, and it is this light that is directly detected.

## Super-Kamiokande

The ability of the Kamiokande experiment to observe the direction of electrons produced in solar neutrino interactions allowed experimenters to directly demonstrate for the first time that the sun was a source of neutrinos.

## Hypotheses

1. Most or all the neutrinos coming from the octant of the Sun originate from above the photosphere.

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