Categories Everything (65) Sound Buttons (9)

## Neutrino

 Composition Elementary particle Fermionic Lepton, antilepton First, second and third Weak interaction and gravitation ν e, ν μ, ν τ, ν e, ν μ, ν τ Antineutrinos are possibly identical to the neutrino (see Majorana fermion). ν e (Electron neutrino): Wolfgang Pauli (1930) ν μ (Muon neutrino): Late 1940s ν τ (Tau neutrino): Mid 1970s ν e: Clyde Cowan, Frederick Reines (1956) ν μ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962) ν τ: DONUT collaboration (2000) 3 – electron neutrino, muon neutrino and tau neutrino Small, but non-zero. See the mass section. 0 e 1⁄2 −1 −1 −3

A neutrino (English pronunciation: /njuːˈtriːnoʊ/, Italian pronunciation: [neuˈtriːno]) is an electrically neutral, weakly interacting elementary subatomic particle[1] with a small but non-zero mass. Being electrically neutral, it is able to pass through ordinary matter almost unaffected, "like a bullet passing through a bank of fog".[2] The neutrino (meaning "small neutral one") is denoted by the Greek letter ν (nu).

Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge, which means that they are not affected by the electromagnetic forces that act on electrons. Neutrinos are affected only by the weak sub-atomic force, of much shorter range than electromagnetism, and are therefore able to travel great distances through matter without being affected by it. Neutrinos also interact gravitationally with other particles.

Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms. There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. Each type also has a corresponding antiparticle, called an antineutrino. Electron neutrinos (or antineutrinos) result when protons decay, through beta decay, to neutrons, or vice versa. Interactions involving neutrinos are mediated by the weak interaction.

Most neutrinos passing through the Earth emanate from the Sun. About 65 billion (6.5×1010) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.[3]

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## History

### Pauli's proposal

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.

The neutrino[nb 1] was first postulated in 1930 by Wolfgang Pauli to preserve the conservation of energy, conservation of momentum, and conservation of angular momentum in beta decay—the decay of an atomic nucleus (not known to contain or involve the neutron at the time) into a proton, an electron and an antineutrino.[nb 2][4]

n0
p+
+ e
+ ν
e

He theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles.

Pauli originally named his proposed light particle a neutron. When James Chadwick discovered a much more massive nuclear particle in 1932 and also named it a neutron, this left the two particles with the same name. Enrico Fermi, who developed the theory of beta decay, coined the term neutrino in 1934 as a way to resolve the confusion. It is the Italian equivalent of "little neutral one".[5]

### Direct detection

In 1942 Kan-Chang Wang first proposed the use of beta-capture to experimentally detect neutrinos.[6] In the July 20, 1956 issue of Science, Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire published confirmation that they had detected the neutrino,[7][8] a result that was rewarded almost forty years later with the 1995 Nobel Prize.[9]

In this experiment, now known as the Cowan–Reines neutrino experiment, neutrinos 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) 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 now known that both the proposed and the observed particles were antineutrinos.

### Neutrino flavor

In 1962 Leon M. Lederman, Melvin Schwartz and Jack Steinberger showed that more than one type of neutrino exists by first detecting interactions of the muon neutrino (already hypothesised with the name neutretto[10]), which earned them the 1988 Nobel Prize. When the third type of lepton, the tau, was discovered in 1975 at the Stanford Linear Accelerator Center, it too was expected to have an associated neutrino (the tau neutrino). First evidence for this third neutrino type came from the observation of missing energy and momentum in tau decays analogous to the beta decay leading to the discovery of the neutrino. The first detection of tau neutrino interactions was announced in summer of 2000 by the DONUT collaboration at Fermilab, making it the latest particle of the Standard Model to have been directly observed; its existence had already been inferred by both theoretical consistency and experimental data from the Large Electron–Positron Collider.

### The solar neutrino problem

Starting in the late 1960s, several experiments found that the number of electron neutrinos arriving from the Sun 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. It was resolved by discovery of neutrino oscillation and mass. (The Standard Model of particle physics had assumed that neutrinos are massless and cannot change flavor. However, if neutrinos had mass, they could change flavor, or oscillate between flavors).

### 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 years he developed the mathematical formalism and the modern formulation of vacuum oscillations. In 1985 Stanislav Mikheyev and 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.

Starting in 1998, experiments began to show that solar and atmospheric neutrinos change flavors (see Super-Kamiokande and Sudbury Neutrino Observatory). This resolved the solar neutrino problem: the electron neutrinos produced in the Sun had partly changed into other flavors which the experiments could not detect.

Although individual experiments, such as the set of solar neutrino experiments, are consistent with non-oscillatory mechanisms of neutrino flavor conversion, taken altogether, neutrino experiments imply the existence of neutrino oscillations. Especially relevant in this context are the reactor experiment KamLAND and the accelerator experiments such as MINOS. The KamLAND experiment has indeed identified oscillations as the neutrino flavor conversion mechanism involved in the solar electron neutrinos. Similarly MINOS confirms the oscillation of atmospheric neutrinos and gives a better determination of the mass squared splitting.[11]

### Supernova neutrinos

Raymond Davis Jr. and Masatoshi Koshiba were jointly awarded the 2002 Nobel Prize in Physics; Davis for his pioneer work on cosmic neutrinos and Koshiba for the first real time observation of supernova neutrinos. The detection of solar neutrinos, and of neutrinos of the SN 1987A supernova in 1987 marked the beginning of neutrino astronomy.

## Properties and reactions

The neutrino has half-integer spin (½±) and is therefore a fermion. Neutrinos interact primarily through the weak force. The discovery of neutrino flavor oscillations implies that neutrinos have mass. The existence of a neutrino mass strongly suggests the existence of a tiny neutrino magnetic moment[12] of the order of 10−19 μB, allowing the possibility that neutrinos may interact electromagnetically as well. An experiment done by C. S. Wu at Columbia University showed that neutrinos always have left-handed chirality.[13] 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, don't need to be considered for the detection experiment. Within a cubic metre 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.

### MSW effect

Neutrinos traveling through matter, in general, undergo a process analogous to light traveling through a transparent material. This process is not directly observable because it doesn't produce ionizing radiation, but gives rise to the MSW effect. Only a small fraction of the neutrino's energy is transferred to the material.

### Nuclear reactions

Neutrinos can interact with a nucleus, changing it to another nucleus. This process is used in radiochemical neutrino detectors. 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.

### Alteration of nuclear decay rate

A Russian study suggests that the decay rate of radioactive isotopes is not constant as is commonly believed,[14] and a recent study[15] also finds this, and says it appears to be affected by the rate of neutrinos emitted by the Sun.

### Induced fission

Very much like neutrons do in nuclear reactors, neutrinos can induce fission reactions within heavy nuclei.[16] So far, this reaction has not been measured in a laboratory, but is predicted to happen within stars and supernovae. The process affects the abundance of isotopes seen in the universe.[17]

### Types of neutrinos

Neutrinos in the Standard Model
of elementary particles
Fermion Symbol Mass[nb 3]
Generation 1
Electron neutrino ν
e
< 2.2 eV
Electron antineutrino ν
e
< 2.2 eV
Generation 2
Muon neutrino ν
μ
< 170 keV
Muon antineutrino ν
μ
< 170 keV
Generation 3
Tau neutrino ν
τ
< 15.5 MeV
Tau antineutrino ν
τ
< 15.5 MeV

There are three known types (flavors) of neutrinos: electron neutrino ν
e
, muon neutrino ν
μ
and tau neutrino ν
τ
, named after their partner leptons in the Standard Model (see table at right). The current best measurement of the number of neutrino types comes from observing the decay of the Z boson. This particle can decay into any light neutrino and its antineutrino, and the more types of light neutrinos[nb 4] available, the shorter the lifetime of the Z boson. Measurements of the Z lifetime have shown that the number of light neutrino types is 3.[12] The correspondence between the six quarks 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. However, actual proof that there are only three kinds of neutrinos remains an elusive goal of particle physics.

The possibility of sterile neutrinos—relatively light neutrinos which do not participate in the weak interaction but which could be created through flavor oscillation (see below)—is unaffected by these Z-boson-based measurements, and the existence of such particles is in fact hinted by experimental data from the LSND experiment. However, the currently running MiniBooNE experiment suggested, until recently, that sterile neutrinos are not required to explain the experimental data,[18] although the latest research into this area is on-going and anomalies in the MiniBooNE data may allow for exotic neutrino types, including sterile neutrinos.[19] A recent re-analysis of reference electron spectra data from the Institut Laue-Langevin[20] has also hinted at a fourth, sterile neutrino.[21]

Recently analyzed data from the Wilkinson Microwave Anisotropy Probe of the cosmic background radiation is compatible with either three or four types of neutrinos. It is hoped that the addition of two more years of data from the probe will resolve this uncertainty.[22]

### Antineutrinos

Annihilation
v · d · e

Antineutrinos are the antiparticles of neutrinos, which are neutral particles produced in nuclear beta decay. These are emitted in beta particle emissions, where a neutron turns into a proton. They have a spin of ½, and are part of the lepton family of particles. The antineutrinos observed so far all have right-handed helicity (i.e. only one of the two possible spin states has ever been seen), while the neutrinos are left-handed. Antineutrinos, like neutrinos, interact with other matter only through the gravitational and weak forces, making them very difficult to detect experimentally. Neutrino oscillation experiments indicate that antineutrinos have mass, but beta decay experiments constrain that mass to be very small. A neutrino-antineutrino interaction has been suggested in attempts to form a composite photon with the neutrino theory of light.

Because antineutrinos and neutrinos are neutral particles it is possible that they are actually the same particle. Particles which have this property are known as Majorana particles. If neutrinos are indeed Majorana particles then the neutrinoless double beta decay process is allowed. Several experiments have been proposed to search for this process.

Researchers around the world have begun to investigate the possibility of using antineutrinos for reactor monitoring in the context of preventing the proliferation of nuclear weapons.[23][24][25]

Antineutrinos were first detected as a result of their interaction with protons in a large tank of water. This was installed next to a nuclear reactor as a controllable source of the antineutrinos. (See: Cowan–Reines neutrino experiment)

### Flavor oscillations

Neutrinos are most often created or detected with a well defined flavor (electron, muon, tau). However, in a phenomenon known as neutrino flavor oscillation, neutrinos are able to oscillate between the three available flavors while they propagate through space. Specifically, this occurs because the neutrino flavor eigenstates are not the same as the neutrino mass eigenstates (simply called 1, 2, 3). This allows for a neutrino that was produced as an electron neutrino at a given location to have a calculable probability to be detected as either a muon or tau neutrino after it has traveled to another location. This quantum mechanical effect was first hinted by the discrepancy between the number of electron neutrinos detected from the Sun's core failing to match the expected numbers, dubbed as the "solar neutrino problem". In the Standard Model the existence of flavor oscillations implies nonzero differences between the neutrino masses, because the amount of mixing between neutrino flavors at a given time depends on the differences in their squared-masses. There are other possibilities in which neutrino can oscillate even if they are massless. If Lorentz invariance is not an exact symmetry, neutrinos can experience Lorentz-violating oscillations.[26]

It is possible that the neutrino and antineutrino are in fact the same particle, a hypothesis first proposed by the Italian physicist Ettore Majorana. The neutrino could transform into an antineutrino (and vice versa) by flipping the orientation of its spin state.[27]

This change in spin would require the neutrino and antineutrino to have nonzero mass, and therefore travel slower than light, because such a spin flip, caused only by a change in point of view, can take place only if inertial frames of reference exist that move faster than the particle: such a particle has a spin of one orientation when seen from a frame which moves slower than the particle, but the opposite spin when observed from a frame that moves faster than the particle.

### Speed

Before the idea of neutrino oscillations came up, it was generally assumed that neutrinos travel at the speed of light. The question of neutrino velocity is closely related to their mass. According to relativity, if neutrinos are massless, they must travel at the speed of light. However, if they carry a mass, they cannot reach the speed of light.

In the early 1980s, first measurements of neutrino speed were done using pulsed pion beams (produced by pulsed proton beams hitting a target). The pions decayed producing neutrinos, and the neutrino interactions observed within a time window in a detector at a distance were consistent with the speed of light. This measurement has been repeated using the MINOS detectors, which found the speed of GeV neutrinos to be 1.000051(29) c. While the central value is higher than the speed of light, the uncertainty is great enough that it is very likely that the true velocity is not greater than the speed of light. This measurement set an upper bound on the mass of the muon neutrino of 50 MeV at 99% confidence.[28]

The same observation was made, on a somewhat larger scale, with supernova 1987A (SN 1987A). The neutrinos from the supernova were detected within a time window that was consistent with a speed of light for the neutrinos. So far, the question of neutrino masses cannot be decided based on measurements of the neutrino speed.

In September 2011 the OPERA collaboration released calculations showing neutrino velocities exceeding the speed of light in their experiments.[29][30] The authors write, "Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly."[29] This result had not been detected by previous experiments, and lies in contrast to several others. For instance, photons and neutrinos from SN 1987A were observed to have an agreement in transit time to about 1 part in 450 million, with even this difference being accounted for by light being impeded by the material of the star early in its journey. The OPERA results, in contrast, suggested that neutrinos were traveling faster than light by a factor of 1 in 40,000,[nb 5] i.e. that neutrino speed is 1.0000248(28) c. Had neutrinos from SN 1987A traveled faster than light by this factor, they would have arrived at Earth several years before the photons; this was not observed to be the case.[nb 6][31] However, neutrinos from the supernova had orders of magnitude less energy than the neutrinos observed in the OPERA experiment, as the authors point out.

The idea that neutrinos could have a tachyonic nature was proposed as far back as 1985 by Chodos et al.[32][33] Today, the possibility of having standard particles moving at superluminal speeds is a natural consequence of unconventional dispersion relations that appear in the Standard-Model Extension,[34][35][36] a realistic description of the possible violation of Lorentz invariance in field theory. In this framework, neutrinos experience Lorentz-violating oscillations and can travel faster than light at high energies.

### Mass

The Standard Model of particle physics assumed that neutrinos are massless, although adding massive neutrinos to the basic framework is not difficult. Indeed, the experimentally established phenomenon of neutrino oscillation requires neutrinos to have nonzero masses.[18] This was originally conceived by Bruno Pontecorvo in the 1950s.

The strongest upper limit on the masses of neutrinos comes from cosmology: the Big Bang model predicts that there is a fixed ratio between the number of neutrinos and the number of photons in the cosmic microwave background. If the total energy of all three types of neutrinos exceeded an average of 50 eV per neutrino, there would be so much mass in the universe that it would collapse.[citation needed] This limit can be circumvented by assuming that the neutrino is unstable; however, there are limits within the Standard Model that make this difficult. A much more stringent constraint comes from a careful analysis of cosmological data, such as the cosmic microwave background radiation, galaxy surveys, and the Lyman-alpha forest. These indicate that the combined mass of the three neutrino varieties must be less than 0.3 eV.[37]

In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos can oscillate from one flavor to another, which requires that they must have a nonzero mass.[38] While this shows that neutrinos have mass, the absolute neutrino mass scale is still not known. This is because neutrino oscillations are sensitive only to the difference in the squares of the masses.[39] The best estimate of the difference in the squares of the masses of mass eigenstates 1 and 2 was published by KamLAND in 2005: Δm2
21 = 0.000079 eV2.[40] In 2006, the MINOS experiment measured oscillations from an intense muon neutrino beam, determining the difference in the squares of the masses between neutrino mass eigenstates 2 and 3. The initial results indicate |Δm2
32| = 0.0027 eV2, consistent with previous results from Super-Kamiokande.[41] Since |Δm2
32| is the difference of two squared masses, at least one of them has to have a value which is at least the square root of this value. Thus, there exists at least one neutrino mass eigenstate with a mass of at least 0.04 eV.[42]

In 2009 lensing data of a galaxy cluster were analyzed to predict a neutrino mass of about 1.5 eV.[43] All neutrino masses are then nearly equal, with neutrino oscillations of order meV. They lie below the Mainz-Troitsk[clarification needed] upper bound of 2 eV for the electron anti-neutrino. The latter will be tested in 2015 in the KATRIN experiment, that searches for a mass between 0.2 eV and 2 eV. If it is found around 1.5 eV, then the Cold Dark Matter particle likely does not exist.[clarification needed]

Currently a number of efforts are under way to directly determine the absolute neutrino mass scale in laboratory experiments. The methods applied involve nuclear beta decay (KATRIN and MARE) or neutrinoless double beta decay (e.g. GERDA, CUORE/Cuoricino, NEMO-3 and others).

In May 2010, it was reported that physicists from CERN and the Italian National Institute for Nuclear Physics' Gran Sasso National Laboratory had observed for the first time a transformation in neutrinos; evidence that they have mass.[44][45]

In July 2010 the 3-D MegaZ experiment reported that they had measured the upper limit of the combined mass of the three neutrino varieties to be less than 0.28 eV.[46]

### Handedness

Experimental results show that (nearly) all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error. In the massless limit, it means that only one of two possible chiralities is observed for either particle. These are the only chiralities included in the Standard Model of particle interactions.

It is possible that their counterparts (right-handed neutrinos and left-handed antineutrinos) simply do not exist. If they do, their properties are substantially different from observable neutrinos and antineutrinos. It is theorized that they are either very heavy (on the order of GUT scale—see Seesaw mechanism), do not participate in weak interaction (so-called sterile neutrinos), or both.

The existence of nonzero neutrino masses somewhat complicates the situation. Neutrinos are produced in weak interactions as chirality eigenstates. However, chirality of a massive particle is not a constant of motion; helicity is, but the chirality operator does not share eigenstates with the helicity operator. Free neutrinos propagate as mixtures of left- and right-handed helicity states, with mixing amplitudes on the order of mν/E. This does not significantly affect the experiments, because neutrinos involved are nearly always ultrarelativistic, and thus mixing amplitudes are vanishingly small. For example, most solar neutrinos have energies on the order of 100 keV1 MeV, so the fraction of neutrinos with "wrong" helicity among them cannot exceed 10−10.[47][48]

## Neutrino sources

### Artificial

Nuclear reactors are the major source of human-generated neutrinos. Anti-neutrinos are made in the beta-decay of neutron-rich daughter fragments in the fission process. Generally, the four main isotopes contributing to the anti-neutrino flux are 235
U
, 238
U
, 239
Pu
and 241
Pu
(i.e. the anti-neutrinos emitted during beta-minus decay of their respective fission fragments). The average nuclear fission releases about 200 MeV of energy, of which roughly 4.5% (or about 9 MeV)[49] is radiated away as anti-neutrinos. For a typical nuclear reactor with a thermal power of 4,000 MW, meaning that the core produces this much heat, and an electrical power generation of 1,300 MW, the total power production from fissioning atoms is actually 4,185 MW, of which 185 MW is radiated away as anti-neutrino radiation and never appears in the engineering. This is to say, 185 MW of fission energy is lost from this reactor and does not appear as heat available to run turbines, since the anti-neutrinos penetrate all building materials essentially tracelessly, and disappear.[50]

The anti-neutrino energy spectrum depends on the degree to which the fuel is burned (plutonium-239 fission anti-neutrinos on average have slightly more energy than those from uranium-235 fission), but in general, the detectable anti-neutrinos from fission have a peak energy between about 3.5 and 4 MeV, with a maximal energy of about 10 MeV.[51] There is no established experimental method to measure the flux of low energy anti-neutrinos. Only anti-neutrinos with an energy above threshold of 1.8 MeV can be uniquely identified (see neutrino detection below). An estimated 3% of all anti-neutrinos from a nuclear reactor carry an energy above this threshold. An average nuclear power plant may generate over 1020 anti-neutrinos per second above this threshold, and a much larger number which cannot be seen with present detector technology.

Some particle accelerators have been used to make neutrino beams. The technique is to smash protons into a fixed target, producing charged pions or kaons. These unstable particles are then magnetically focused into a long tunnel where they decay while in flight. Because of the relativistic boost of the decaying particle the neutrinos are produced as a beam rather than isotropically. Efforts to construct an accelerator facility where neutrinos are produced through muon decays are ongoing.[52] Such a setup is generally known as a neutrino factory.

Nuclear bombs 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.[53]

### Geological

Neutrinos are part of the natural background radiation. In particular, the decay chains of 238
U
and 232
Th
isotopes, as well as40
K, include beta decays which emit anti-neutrinos. 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 anti-neutrinos coming from reactors. Several future experiments aim at improving the geoneutrino measurement and these will necessarily have to be far away from reactors.

Solar neutrinos (proton-proton chain) in the Standard Solar Model

### Atmospheric

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.

### Solar

Solar neutrinos originate from the nuclear fusion powering the Sun and other stars. The details of the operation of the Sun are explained by the Standard Solar Model. In short: when four protons fuse to become one helium nucleus, two of them have to convert into neutrons, and each such conversion releases one electron neutrino.

The Sun sends enormous numbers of neutrinos in all directions. Every second, about 65 billion (6.5×1010) solar neutrinos pass through every square centimeter on the part of the Earth that faces the Sun.[3] 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.

### By supernovae

Neutrinos are an important product of Types Ib, Ic and II (core-collapse) supernovae. In such events, the density at the core becomes so high (1017 kg/m3) that the degeneracy of electrons is not enough to prevent protons and electrons from combining to form a neutron and an electron neutrino. A second and more important neutrino source is the thermal energy (100 billion kelvins) of the newly formed neutron core, which is dissipated via the formation of neutrino-antineutrino pairs of all flavors.[54] Most of the energy produced in supernovas is thus radiated away in the form of an immense burst of neutrinos. The first experimental evidence of this phenomenon came in 1987, when neutrinos from supernova 1987A were detected. The water-based detectors Kamiokande II and IMB detected 11 and 8 antineutrinos of thermal origin,[54] 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. It is thought that neutrinos would also be produced from other events such as the collision of neutron stars. The neutrino signal from the supernova arrived at earth several hours before the arrival of the first electromagnetic radiation, as expected from the evident fact that the latter emerges along with the shock wave. The exceptionally feeble interaction with normal matter allowed the neutrinos to pass through the churning mass of the exploding star, while the electromagnetic photons were slowed.

Because neutrinos interact so little with matter, it is thought that a supernova's neutrino emissions carry information about the innermost regions of the explosion. Much of the visible light comes from the decay of radioactive elements produced by the supernova shock wave, and even light from the explosion itself is scattered by dense and turbulent gases. Neutrinos, on the other hand, pass through these gases, providing information about the supernova core (where the densities were large enough to influence the neutrino signal). Furthermore, the neutrino burst is expected to reach Earth before any electromagnetic waves, including visible light, gamma rays or radio waves. The exact time delay depends on the velocity of the shock wave and on the thickness of the outer layer of the star. For a Type II supernova, astronomers expect the neutrino flood to be released seconds after the stellar core collapse, while the first electromagnetic signal may emerge hours later. The SNEWS project uses a network of neutrino detectors to monitor the sky for candidate supernova events; the neutrino signal will provide a useful advance warning of a star exploding in the Milky Way.

### By supernova remnants

The energy of supernova neutrinos ranges from a few to several tens of MeV. However, 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: the supernova remnants. The origin of the cosmic rays was attributed to supernovas by Walter Baade and Fritz Zwicky; this hypothesis was refined by Vitaly L. Ginzburg and Sergei I. 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 percent. 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, AMANDA, IceCube, Antares, NEMO and Nestor. Related information is provided by very high energy gamma ray observatories, such as VERITAS, HESS and MAGIC. Indeed, the collisions of cosmic rays are supposed to produce charged pions, whose decay give the neutrinos, and also neutral pions, whose decay give gamma rays: the environment of a supernova remnant 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 ANITA.

### By the Big Bang

It is thought that, just like the cosmic microwave background radiation left over 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: we know they exist. However, they also have serious problems.

From particle experiments, it is known that neutrinos are very light. This means that they move at speeds close to the speed of light. Thus, dark matter made from neutrinos is termed "hot dark matter". The problem is that being fast moving, the neutrinos would tend to have spread out evenly in the universe before cosmological expansion made them cold enough to congregate in clumps. This would cause the part of dark matter made of neutrinos to be smeared out and unable to cause the large galactic structures that we see.

Further, these same galaxies and groups of galaxies appear to be surrounded by dark matter which is not fast enough to escape from those galaxies. Presumably this matter provided the gravitational nucleus for formation. This implies that neutrinos make up only a small part of the total amount of dark matter.

From cosmological arguments, relic background neutrinos are estimated to have density of 56 of each type per cubic centimeter and temperature 1.9 K (1.7×10−4 eV) if they are massless, much colder if their mass exceeds 0.001 eV. Although their density is quite high, due to extremely low neutrino cross-sections at sub-eV energies, the relic neutrino background has not yet been observed in the laboratory. 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 6 orders of magnitude.

## Neutrino detection

Neutrinos cannot be detected directly, because they don't ionize the materials they are passing through (they don't carry electric charge and other proposed effects, like the MSW effect, do not produce traceable radiation). A unique reaction to identify anti-neutrinos, sometimes referred to as inverse beta decay, as applied by Reines and Cowan (see below), requires a very large detector in order to detect a significant number of neutrinos. All detection methods require the neutrinos to carry a minimum threshold energy. So far, there is no detection method for low energy neutrinos, in the sense that potential neutrino interactions (for example by the MSW effect) cannot be uniquely distinguished from other causes. Neutrino detectors are often built underground in order to isolate the detector from cosmic rays and other background radiation.

Antineutrinos were first detected in the 1950s near a nuclear reactor. Reines and Cowan used two targets containing a solution of cadmium chloride in water. Two scintillation detectors were placed next to the cadmium targets. Antineutrinos with an energy above the threshold of 1.8 MeV caused charged current interactions with the protons in the water, producing positrons and neutrons. This is very much like β+
decay, where energy is used to convert a proton into a neutron, a positron (e+
) and an electron neutrino (ν
e
) is emitted:

From known β+
decay:

$\rm{Energy} + p \rightarrow n + e^+ + {\nu_e}$

In the Cowan and Reines experiment, instead of an outgoing neutrino, you have an incoming anti-neutrino (ν
e
) from a nuclear reactor:

$\rm{Energy}(>1.8 MeV) + p + \bar{\nu_e} \rightarrow n + e^+$

The resulting positron annihilation with electrons in the detector material created photons with an energy of about 0.5 MeV. Pairs of photons in coincidence could be detected by the two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei resulting in gamma rays of about 8 MeV that were detected a few microseconds after the photons from a positron annihilation event.

Since then, various detection methods have been used. Super Kamiokande is a large volume of water surrounded by photomultiplier tubes 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 uses 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 uses a solid plastic scintillator coupled to photomultiplier tubes, while Borexino uses a liquid pseudocumene scintillator also watched by photomultiplier tubes and the proposed NOνA detector will use liquid scintillator watched by avalanche photodiodes. The IceCube Neutrino Observatory uses 1 km3 of the Antarctic ice sheet near the south pole with photomultiplier tubes distributed throughout the volume.

## Motivation for scientific interest

The neutrino is of scientific interest because it can make an exceptional probe for environments that are typically concealed from the standpoint of other observation techniques, such as optical and radio observation.

The first such use of neutrinos was proposed in the early 20th century for observation of the core of the Sun. Direct optical observation of the solar core is impossible due to the diffusion of electromagnetic radiation by the huge amount of matter surrounding the core. On the other hand, neutrinos generated in stellar fusion reactions interact very weakly with matter, and pass through the Sun with few interactions. While photons emitted by the solar core may require some 40,000 years to diffuse to the outer layers of the Sun, neutrinos are virtually unimpeded and cross this distance at nearly the speed of light.[55][56]

Neutrinos are also useful for probing astrophysical sources beyond our solar system. Neutrinos are the only known particles that are not significantly 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 not able to travel more than about 100 megaparsecs due to the GZK cutoff. Neutrinos can travel this and greater distances with very little attenuation.

The galactic core of the Milky Way is completely obscured by dense gas and numerous bright objects. Neutrinos produced in the galactic core will be measurable by Earth-based neutrino telescopes in the next decade.

Another important use of the neutrino is in the observation of supernovae, the explosions that end the lives of highly massive stars. The core collapse phase of a supernova is an almost unimaginably dense and energetic event. It is so dense that no known particles are able to escape the advancing core front except for neutrinos. Consequently, supernovae are known to release approximately 99% of their energy in a quick (10-second) burst of neutrinos. As a result, neutrinos are a very useful probe for these important events.

Determining the mass of the neutrino (see above) is also an important test of cosmology (see Dark matter). The astrophysical significance of the neutrino as an observational technique is comparable with all other known techniques, and is therefore a major focus of study in astrophysical communities.

In particle physics the main virtue of studying neutrinos is that they are typically the lowest mass, and hence lowest energy examples of particles theorized in extensions of the Standard Model of particle physics. For example, one would expect that if there is a fourth class of fermions beyond the electron, muon, and tau generations of particles, that the fourth generation neutrino would be the easiest to generate in a particle accelerator.

Neutrinos could also be used for studying quantum gravity effects. Because they are not affected by either the strong interaction or electromagnetism (unless they have a magnetic moment), and because they are not normally found in composite particles (unlike quarks) or prone to near instantaneous decay (like many other standard model particles) it might be possible to isolate and measure gravitational effects on neutrinos at a quantum level.

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 There is no such thing as time Posted by Bling King Apr 4th Upon further ponderance I have come to the conclusion that time does not exist except in the law of physics. I have come to this conclusion through the observation of how things change and why they change at the pace in which they change. To me it seems that every change that takes place  in the universe is not dictated by time but rather physics. It is the law of physics that dictates the rate and speed at which all things change. For example if you have a car  that is traveling at 100 miles an hour the speed at  which the car travels is all dictated by physical changes and therfor controlled by the law of physics..Therfor it seems that for any change to take place all you need is physics and the law of physics that governs the physical changes. Time does not need be a factor and bears no relavance. As long as we have the law of physics everything will happen in accordance with those laws. Comments?(0)
 The composition of time Posted by Bling King Mar 25th Time has 3 components. A front a middle and a rear. In the front time has what appears to be something of perspectual perspectualness that will move things forward at a set forth proponent. This part of time is easy to see and witness. However it is not easy to predict at which point time will make forward momentum happen. It would seem that this forward momentum is always in inactment but I would disagree with this. To me it seems more as if time interacts with things on its own accord leaving somethings unchanged for long standing periods of time. An example of this would be how time occasionally interacts with the speed of light. The speed of light remains constant but occasionally time will manifest itself into the equation and make modifications of the speed that light travels. For instance light will move forward forthwittingly at a billion miles a second but if it encounters any kind of resistance then time will inject itself and change the speed at which it was moving. Which leads me to the assumption that in order for time to inject itself into any equation a proponent has to take place that makes a physical change that would cause time to interject itself. If no physical change takes place than time has also not been a factor.     The middle proponent of time is the area in which time is manipulating  the change that takes...Read More Comments?(0)
 👄What turns me on Posted by Bling King Feb 23rd I get turned on by some funny stuff. I'm not really into like full blown kinkiness or at least I wouldn't consider myself to be a kinky person but I do have a few fetishes. Some of them are a little out of the ordinary. For instance I have this one fetish about being tied up  and thrown in the ocean and then rescued by a mermaid. I think this fantasy comes from when I was a kid and I used to dream of mermaids and always wanted to meet one. Well one day its gonna happen. Now don't go telling me mermaids don't exist. You don't know cause they are in fact real and as soon as I meet one I will prove it to you. As far as some of my other turn ons  I guess what really gets me excited is people who  tell other people to shut the fuck up. I love when a woman just looks at a man and tells him to shut his mouth. To me thats a big turn on because the woman seems assertive like a dominatrix or something. If she will be assertive in a conversation she will be assertive in the bedroom or so I  would like to believe. Comments?(0)
 Time is a dialectable derelict Posted by Bling King Feb 12th To fathom the fortrighteousness of time one has to contemplate the personification of forthwittial forthwittil. Time forthwittingly will only listen to the commands of its on inner personification to which there is no directional direction or so it would seem but on further inquisitories I have come to realize that there is a forthwittingly forthwittal of which time has pronounced and those commands seem to speak to the nature of to which time corresponds. To review these pronouncements for your own bemusement look at time as if you had it captured it  in a bottle. What would happen? We know on the inside of the bottle time would force the inner workings of the bottle to correspond to times diabolical commands. Causing everything to change to times everlescent rules. however on the outside of the bottle things would not change, everything would stay in constant neutrality or would it? The question remains if there was no time would things still be allowed to happen and if so at what pace and what would dictate the pace at which things would change. There seems to be no rule in place for the dictation of the pace change which takes place. So it would seem that time has decided that factor somehow within itself. There could be a correlation at which things change and the pace being dictated by physics and the amount the physical world can be allowed to change within its own accord of set boundaries. To actually find...Read More Comments?(0)
 Free from time constraints Posted by Bling King Jan 16th http://ning.spruz.com/gfile/75r4!-!HLKFHG!-!f170qSvyr5/ticking_clock-kevangc-1934595011_(1).mp3 Your browser does not support the audio element.   There was a time when time did not matter. The thing that was an utmost relevance now was of no matter. The diffrence it made seemed miniscule and now it is constantly dictating everything that takes place before me. What is this thing that controls and makes everything manifest itself to its constraints and why and how does it do this. Time is nothing but the utmost miracle before us. Something that has always had to exist for anything ever to take place. There is no changing its course there is no variance in its absolute everlasting existance. To control time would be the utmost  crown jewel of all accomplishments if indeed it could ever be controlled. The only way I ever see time being manipulated to change its values is to speed up everything that time has interacted with. In order to do such a thing you would have to understand the nature of the objects in question and how they are effected by time. For instance a speeding car will slow down in time without constant force being distrubuted by the engine. To slow down the car one only has to take their foot off the accelarator and gradually time will do the rest but if you could freeze time at the speed at which the car was traveling then time would not  exist because the...Read More Comments?(0)
 the truth about time Posted by Bling King Sep 2nd 2018 I have looked at time many times and I have noticed a few components. There is a precise proponent that ushers in a manifestation. Whenever something new is going to happen you can look at that event which is about to take place and precisely predict exactly when it has started. Once you realize a manifestation has taken place you can precisely predict its out come. If you know that a manifestation has started to take place then you will know you are being guided through the realm precisely by the forces of an enlightenment. Throughout time this manifestation will remain constant starting with a beginning and an end and ending in a preconcieved enlightenment. Sometimes an enlightenment can take weeks and some times an enlightenment can take centuries. It depends on how many times that enlightenment has been benounced to the realm. Comments?(0)
 nothing Posted by Bling King Jul 17th 2018 Your browser does not support the audio element. I suspect a suffcient of sufficence of suffiacantel suffiance of suffiance of absurdity of absurdanace. In all actual actuality there is an  actual actuality of actualityness in retrospect to the retorospective respect in which every person who has an intellectual intellect can see that the world is a prominance of prominance in which the order will reside as long as the order is maintained. Once that order is relinquished chaos will ensue. For chaos to be a calamity there only needs to be a perspectual perspective of perspectance that escalates the chaos to that height. What would cause that is a person or persons in the realm of the realmatical realmatics looking beyond thier own existance to the existance of there forfathers to see what has become of thier existance. If you look at your own existance for what it is you will see that it is neither logical nor illogical for it makes all the sense of a sensimatical sensematic. As long as you have a reason for your own existance then it is fruitful for you to exist. Once that reason or reasons are gone you will no longer care whether it is you live or die. In the realm in which we live is a prospectus prospectant of prospectantin which all will ensue. To change the prospectus prospectus you need to look to the realm and see what the prospectus prospectant is and manifest it to your own liking. My...Read More Comments?(0)
 The conclusive conclusion Posted by Bling King Jul 17th 2018 In all actual reality the realm is manifested of certain procedural procedures that come forth frequently to forthrightous forthrightenous. In the place of predicament I have found that I can properly place things in the procedural sequence unbenowst to people of the realm. In order to conflict the conflictions you have to equate the equation of equationalness in to proper equations. Very simple but also very tedious. You do this by equating the equation into percise preciseness. An example of an equation would be a placement of perdicament of a certain event in which you wish it to be. The next manifestation I could manifest is a manifestual manifestation of manifests of a sequance of certainal circumstances. Put together a sequence by asking the sequence in order to manifest itself and then tell the manifestations to happen in frequence in which they will unfold. Comments?(0)
 The Unattainable future Posted by Bling King Jul 17th 2018 If the future is a grain of sand and its falling through an hour glass nothing in the world can stop it. It will eniquivaocalby blind as to where its going when it comes to its rest it has befallen its fate and will remain where it lay for an eternity knowing nothing about itself or it's surroundings. I am that grain of sand. Nothing ever can change my destiny for only time here makes a diffrence.. To benounce the future is the only way to change ones fortune. The time it takes to make an equivical change remains the utmost mystery of the universe. Comments?(0)
 🤯In the eyes of myself Posted by Bling King Jun 30th 2018 Your browser does not support the audio element.   There where three men. All who seemed frightened. They stood on the edge of the canyon looking on as a fourth man tumbled to his death. We could have saved him said one of the men. He should have saved himself said another. The third man just look at them bewildered and brought a handgun to his own head and pulled the trigger. Blood spattered. The two men watched as he slumped to the ground. The first man screamed and the second threw himself to the side of the man on the ground. Why?!! he screamed. It was the only sound heard. Sobbing he looked at the man standing and said you did this! You and your frigging righteous speech about the lives we leave and the sacrifice we must make. Your the devil. I am not the devil said the standing man only the truth. The truth about what? The other man screamed. Your life he said and he jumped. The man heard a ringing and he sat up slowly. It was over the dream but his thoughts where still on the side of the canyon. How did this happen. How did it all just fade away? The dream came and went in an instant leaving his mind boggled and his eyes heavy. I knew I was there thought the man but how? It was all to familiar the...Read More Comments?(0)
 The story Elijah and Ellen Posted by Bling King Jun 6th 2018 The story of Elijah and Ellan. This is the story of Elijah and Ellan. Ellan is a beutiful temptress and Elijah is a dutiful servant of Ellan's. Together the pair fell in love and soon became a duo of in excessible excession. They frolicked in the sun under the rare occurance of rain they took shelter in the arms of each other. One day while hiding from the glares of the sun under an oak tree that provided an abundance of shade they looked into each others souls and realized there where no people suited for each other then the two of them where suited for each other. They basked in the notion that they where the most two compatible souls on the planet. As they where thinking this a giant unforseen acclamaited acclamation occurred. The planet began to tremble and shake beneath them and the stars came out. The sun hid amongst the clouds and everything from start to finish began to take shape. There where huge explosions and giant surges of wind and rain. The two began to run for their shelter knowing at the exact moment the trembling and violent agressions of unacclaimated weather started that they most likely wouldn't make it to see another sunrise. The planet was exploding with molten lava and the tempertures where unbearable as for the two of them could remember they had never seen a winter climate and didn't expect they ever would. The planet had been warming out of...Read More Comments?(0)
 today was a day of dismal despair Posted by Bling King Oct 19th 2017 Things have gone down hill drastically now for a very long time. We seem to be some what defeated but yet i know we still have some power and prominance. We are fighting an up hill battle and there is no way forward from here from what i can see. We are trudging along a path that goes nowhere. Comments?(0)
 ⚔️The Greatest Warrior of All Time Posted by Bling King Mar 2nd 2017 Today i conquered and beat all adverseries there where to beat. Tomorrow new adversaries will arise. I will be ready, there is never a shortage of enemies who wish to dethrone me from the top of the world. I didn't get here by being passive and yeilding to the oppostion. I got here by defeating them both mentally and physically and in entiriety. Comments?(0)
 In a time of desilute despair Posted by Bling King Mar 2nd 2017 Your browser does not support the audio element.      There was a time when I was in desilute despair. The only thing I had was me myself and I to fall back on. I looked at the person who was my opponent and I knew one of  us was going to die and I was going to do everytrhing I could to make dam sure it wasn't me. I pulled my six shooter from its holster and aimed at the guy looking at me  about 30 yards away. He also went for his gun and in lightning speed he was laid sprawled out on the dirt bleeding and moaning. I had heard a shot but new that it had come from my own gun. He never even got a shot off. I was unscathed and again undeafeted. Anybody who ever tried to kill me was dead and their where over 30 who had tried and failed to kill yours truly. Comments?(0)
 Gravity Posted by Bling King Feb 9th 2017 Gravity is the force of nature that pulls cellestrial bodies toward one another. The cause of gravity is the enertia of a bodies movement through space and time. This happens by an object preconcievably traveling through the cosmos at an alarming rate of acceleration. The faster an object travels the more enertia it will build up and then will therefore have a greater ability to move. the more it moves the more other objects will cling to it. the way this can be proved is by taking an object and hurtling it towards another object the two objects would collide do to the enertia pulling them towards each other. Thy would not stay on their current trajectory but their paths would alter towards one another in a greater force than their initial gravitational pull. the best test to accomodate this theory would be tow baseballs flying through the air at speeds over one hundred miles an hour. The baseballs would not interject themselves with one another normally but at this speed would do so do to the balls enertia pulling them towards one another. Comments?(0)
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