73. E = mc2 update to massless energy
Janet Conrad is Associate Prof of Physics at Columbia University.
She is famous for her research on neutrinos.
This is what she said about Newton's E=mc2:
"E=mc2 is not the whole of what Newton wrote as his equation;
It is, E-mc2 being the energy of a body at rest , plus the energy of motion, the motion being at the speed of light."
"So" she says, " if you set mass = 0, we still have energy: Energy of motion.
That being the case, we have massless particles."
She says this concept is important in her study of neutrinos.
(what are neutrinos? Doesnt matter, ask the dog later)
The above is from Google search, Nova/ Janet Conrad/ massless particles should do it.
*********
Where I come in is this massless particle.
I keep harping on about primordial energy, light, Love, etc so if you read these posts you know where I am going:
Scripture:
Hbr 11:1 Now faith is the substance of things hoped for, the evidence of things not seen.
Mat 17:20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
Luk 17:6 And the Lord said, If ye had faith as a grain of mustard seed, ye might say unto this sycamine tree, Be thou plucked up by the root, and be thou planted in the sea; and it should obey you.
Therefore, with tongue in cheek,:
Faith is a massless particle.
It has energy.
Einstein's equation supports it.
And my favorite:
God is Love
1Jo 4:8 He that loveth not knoweth not God; for God is love.
1Jo 4:16 And we have known and believed the love that God hath to us. God is love; and he that dwelleth in love dwelleth in God, and God in him.
Jhn 1:2 The same was in the beginning with God.
Jhn 1:3 All things were made by him; and without him was not any thing made that was made.
Jhn 1:4 In him was life; and the life was the light of men.
Jhn 1:5 And the light shineth in darkness; and the darkness comprehended it not.
Jhn 1:6 There was a man sent from God, whose name [was] John.
Jhn 1:7 The same came for a witness, to bear witness of the Light, that all [men] through him might believe.
Gen 1:1 In the beginning God created the heaven and the earth.
Gen 1:2 And the earth was without form, and void; and darkness [was] upon the face of the deep. And the Spirit of God moved upon the face of the waters.
Gen 1:3 And God said, Let there be light: and there was light
So could we imagine , we might develop the idea that God is everything.
Never mind the dog, Ross's dog.. I wonder what Janet would say?
She is famous for her research on neutrinos.
This is what she said about Newton's E=mc2:
"E=mc2 is not the whole of what Newton wrote as his equation;
It is, E-mc2 being the energy of a body at rest , plus the energy of motion, the motion being at the speed of light."
"So" she says, " if you set mass = 0, we still have energy: Energy of motion.
That being the case, we have massless particles."
She says this concept is important in her study of neutrinos.
(what are neutrinos? Doesnt matter, ask the dog later)
The above is from Google search, Nova/ Janet Conrad/ massless particles should do it.
*********
Where I come in is this massless particle.
I keep harping on about primordial energy, light, Love, etc so if you read these posts you know where I am going:
Scripture:
Hbr 11:1 Now faith is the substance of things hoped for, the evidence of things not seen.
Mat 17:20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
Luk 17:6 And the Lord said, If ye had faith as a grain of mustard seed, ye might say unto this sycamine tree, Be thou plucked up by the root, and be thou planted in the sea; and it should obey you.
Therefore, with tongue in cheek,:
Faith is a massless particle.
It has energy.
Einstein's equation supports it.
And my favorite:
God is Love
1Jo 4:8 He that loveth not knoweth not God; for God is love.
1Jo 4:16 And we have known and believed the love that God hath to us. God is love; and he that dwelleth in love dwelleth in God, and God in him.
Jhn 1:2 The same was in the beginning with God.
Jhn 1:3 All things were made by him; and without him was not any thing made that was made.
Jhn 1:4 In him was life; and the life was the light of men.
Jhn 1:5 And the light shineth in darkness; and the darkness comprehended it not.
Jhn 1:6 There was a man sent from God, whose name [was] John.
Jhn 1:7 The same came for a witness, to bear witness of the Light, that all [men] through him might believe.
Gen 1:1 In the beginning God created the heaven and the earth.
Gen 1:2 And the earth was without form, and void; and darkness [was] upon the face of the deep. And the Spirit of God moved upon the face of the waters.
Gen 1:3 And God said, Let there be light: and there was light
So could we imagine , we might develop the idea that God is everything.
Never mind the dog, Ross's dog.. I wonder what Janet would say?
posted by Ross at 8:30 pm
10 Comments:
So I eventually asked the dog, Ross's dog, "dog , I said, Ross's dog, what the ding dong is a neutrino, in plain English that we can all understand?"
He said, that not being English, though he often thinks of England, he can really only explain it in the following way:
"The neutrino is an elementary particle. It has half-integer spin () and is therefore a fermion. All neutrinos observed to date have left-handed chirality. Although they had been considered massless for many years, recent experiments (see Super-Kamiokande, Sudbury Neutrino Observatory, KamLAND and MINOS) have shown their mass to be non-zero. Because it is an electrically neutral lepton, the neutrino interacts neither by way of the strong nor the electromagnetic force, but only through the weak force and gravity.
Because the cross section in weak nuclear interactions is very small, neutrinos can pass through matter almost unhindered. For typical neutrinos produced in the sun (with energies of a few MeV), it would take approximately one light year (~1016m) of lead to block half of them. Detection of neutrinos is therefore challenging, requiring large detection volumes or high intensity artificial neutrino beams.
He went on to say:
There are different
Types of neutrinos
Neutrinos
in the Standard Model
Fermion Symbol Mass
Generation 1 (electron)
Electron neutrino < 2.2 eV
Electron antineutrino < 2.2 eV
Generation 2 (muon)
Muon neutrino < 170 keV
Muon antineutrino < 170 keV
Generation 3 (tau)
Tau neutrino < 15.5 MeV
Tau antineutrino < 15.5 MeV
There are three known types (flavors) of neutrinos: electron neutrino νe, muon neutrino νμ and tau neutrino ντ, 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 neutrino and its antineutrino, and the more types of neutrinos available, the shorter the lifetime of the Z boson. The latest measurements put the number of light neutrino types (where "light" means having mass less than half the Z mass) at 2.984±0.008[1]. The possibility of sterile neutrinos — 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 supported by experimental data from LSND. The correspondence between the six quarks in the Standard Model and the six leptons, among them the three neutrinos, provides additional evidence that there should be exactly three types. However, conclusive proof that there are only three kinds of neutrinos remains an elusive goal of particle physics.
[edit]
Flavor Oscillations
Neutrinos are always 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 effect was first noticed due to the number of electron neutrinos detected from the sun's core failing to match the expected numbers, a discrepancy dubbed the "solar neutrino problem". The existence of flavor oscillations implies a non-zero neutrino mass, because the amount of mixing between neutrino flavors at a given time depends on the differences in their squared-masses (mixing would be zero for massless neutrinos). Despite their massive nature, it is still possible that the neutrino and antineutrino are in fact the same particle, a hypothesis first proposed by the Italian physicist Ettore Majorana.
[edit]
History
The neutrino was first postulated in 1931 by Wolfgang Pauli to explain the energy spectrum of beta decays, the decay of a neutron into a proton and an electron. Pauli theorized that an undetected particle was carrying away the observed difference between the energy and angular momentum of the initial and final particles. Because of their "ghostly" properties, the first experimental detection of neutrinos had to wait until about 25 years after they were first discussed. In 1956 Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire published the article "Detection of the Free Neutrino: a Confirmation" in Science (see neutrino experiment), a result that was rewarded with the 1995 Nobel Prize.
The name neutrino was coined by Enrico Fermi - who developed the first theory describing neutrino interactions - as a word play on neutrone, the Italian name of the neutron. (Neutrone in Italian means big and neutral, and neutrino means small and neutral.)
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. When a third type of lepton, the tau, was discovered in 1975 at the Stanford Linear Accelerator, it too was expected to have an associated 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 that had led to the discovery of the neutrino in the first place. The first detection of actual 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.
A practical method for investigating neutrino masses (that is, flavour oscillation) was first suggested by Bruno Pontecorvo in 1957 using an analogy with the neutral kaon system; 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 flavour oscillations can be modified when neutrinos propagate through matter. This so-called MSW effect is important to understand neutrinos emitted by the Sun, which pass through its dense atmosphere on their way to detectors on Earth.
[edit]
Mass
The Standard Model of particle physics assumes 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 non-zero masses.
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 electron volts per neutrino, there would be so much mass in the universe that it would collapse. 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, galaxy surveys and the Lyman-alpha forest. These indicate that the sum of the neutrino masses must be less than 0.3 electron volts (Goobar, 2006).
In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos do indeed flavour oscillate, and therefore have mass. The experiment is only sensitive to the difference in the squares of the masses. These differences are known to be very small, less than 0.05 electron volts (Mohapatra, 2005). Combined, these constraints imply that the heaviest neutrino must be at least 0.05 electron volts, but no more than 0.3 electron volts.
The best estimate of the difference between the mass eigenstates 1 and 2 was published by KamLAND in 2005: Δm212 = 0.000079 eV2
In 2006, the MINOS experiment measured oscillations from an intense muon neutrino beam, determining the squared mass difference between neutrino mass eigenstates 2 and 3. The initial results indicate Δm232 = 0.0031 eV2, consistent with previous results from Super-K . [2]
[edit]
Neutrino sources
[edit]
Human generated
Nuclear power stations are the major source of human-generated neutrinos. The 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: uranium-235, uranium-238, plutonium-239 and plutonium-241. An average plant may generate over 1020 anti-neutrinos per second.
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 focussed 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.
Nuclear bombs also produce very large numbers of neutrinos. Fred Reines and Clyde Cowan thought about trying to detect neutrinos from a bomb before they switched to looking for reactor neutrinos.
[edit]
The Earth
Neutrinos are produced as a result of natural background radiation. In particular, the decay chains of uranium-238 and thorium-232 isotopes, as well as potassium-40, 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.
[edit]
Atmospheric neutrinos
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 (TIFR), Mumbai, Osaka City Univeristy, Japan and Durham University, UK recorded the first cosmic ray neutrino interaction in an underground laboratory in KGF mines in 1965.
[edit]
Solar neutrinos
Solar neutrinos originate from the nuclear fusion powering the Sun and other stars.
Raymond Davis Jr. and Masatoshi Koshiba were jointly awarded the 2002 Nobel Prize in Physics for their work in the detection of cosmic neutrinos.
[edit]
Cosmological phenomena
Neutrinos are an important product of supernovae. In such events, the pressure at the core becomes so high (1014 g/cm3) that the degeneracy of electrons is not enough to prevent protons and electrons from combining to form a neutron and an electron neutrino. Most of the energy produced in supernovae is radiated away in the form of an immense burst of neutrinos. The first experimental evidence of this phenomenon came in the year 1987, when neutrinos coming from the supernova 1987a were detected. It is thought that neutrinos would also be produced from other events such as the collision of neutron stars.
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 is unknown, but 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 be hours or days later. The SNEWS project uses a network of neutrino detectors to monitor the sky for candidate supernova events; it is hoped that the neutrino signal will provide a useful advance warning of an exploding star.
[edit]
Cosmic background radiation
It is thought that the cosmic background radiation left over from the Big Bang includes a background of low energy neutrinos. 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 except when they have extremely little kinetic energy. 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 currently be surrounded by dark matter which is not now fast moving enough to escape from those galaxies, and presumably provided the gravitational nucleus for their formation. All of this suggests that neutrinos make up only a small part of all dark matter.
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Neutrino detection
Neutrinos can interact via the neutral current (involving the exchange of a Z boson) or charged current (involving the exchange of a W boson) weak interactions.
In a neutral current interaction, the neutrino leaves the detector after having transferred some of its energy and momentum to a target particle. All three neutrino flavors can participate regardless of the neutrino energy. However, no neutrino flavor information is left behind.
In a charged current interaction, the neutrino transforms into its partner lepton (electron, muon, or tau). However, if the neutrino does not have sufficient energy to create its heavier partner's mass, the charged current interaction is unavailable to it. Solar and reactor neutrinos have enough energy to create electrons. Most accelerator-based neutrino beams can also create muons, and a few can create taus. A detector which can distinguish among these leptons can reveal the flavor of the incident neutrino in a charged current interaction. Because the interaction involves the exchange of a charged boson, the target particle also changes character (e.g., neutron → proton).
Antineutrinos were first detected in 1953 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. Antineutrino charged current interactions with the protons in the water produced positrons and neutrons. The resulting positron annihilations with electrons 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. Today, the much larger KamLAND detector uses similar techniques and 53 Japanese nuclear power plants to study neutrino oscillation.
Chlorine detectors consist of a tank filled with carbon tetrachloride. A neutrino converts a chlorine atom into one of argon via the charged current interaction. The fluid is periodically purged with helium gas which would remove the argon. The helium is then cooled to separate out the argon. A chlorine detector in the former Homestake Mine near Lead, South Dakota, containing 520 short tons (470 metric tons) of fluid, made the first measurement of the deficit of electron neutrinos from the sun (see solar neutrino problem). A similar detector design uses a gallium → germanium transformation which is sensitive to lower energy neutrinos. These chemical detection methods are useful only for counting neutrinos; no neutrino direction or energy information is available.
"Ring-imaging" detectors take advantage of the Cherenkov light produced by charged particles moving through a medium faster than the speed of light in that medium. In these detectors, a large volume of clear material (e.g., water) is surrounded by light-sensitive photomultiplier tubes. A charged lepton produced with sufficient energy creates Cherenkov light which leaves a characteristic ring-like pattern of activity on the array of photomultiplier tubes. This pattern can be used to infer direction, energy, and (sometimes) flavor information about the incident neutrino. Two water-filled detectors of this type (Kamiokande and IMB) recorded the neutrino burst from supernova 1987a. The largest such detector is the water-filled Super-Kamiokande.
The Sudbury Neutrino Observatory (SNO) uses heavy water. In addition to the neutrino interactions available in a regular water detector, the deuterium in the heavy water can be broken up by a neutrino. The resulting free neutron is subsequently captured, releasing a burst of gamma rays which are detected. All three neutrino flavors participate equally in this dissociation reaction.
The MiniBooNE detector employs pure mineral oil as its detection medium. Mineral oil is a natural scintillator, so charged particles without sufficient energy to produce Cherenkov light can still produce scintillation light. This allows low energy muons and protons, invisible in water, to be detected.
Tracking calorimeters such as the MINOS detectors (see the NuMI-MINOS project page) use alternating planes of absorber material and detector material. The absorber planes provide detector mass while the detector planes provide the tracking information. Steel is a popular absorber choice, being relatively dense and inexpensive and having the advantage that it can be magnetised. The Noνa proposal suggests the use of particle board as a cheap way of getting a large amount of less dense mass. The active detector is often liquid or plastic scintillator, read out with photomultiplier tubes, although various kinds of ionisation chambers have also been used. Tracking calorimeters are only useful for high energy (GeV range) neutrinos. At these energies, neutral current interactions appear as a shower of hadronic debris and charged current interactions are identified by the presence of the charged lepton's track (possibly alongside some form of hadronic debris.) A muon produced in a charged current interaction leaves a long penetrating track and is easy to spot. The length of this muon track and its curvature in the magnetic field provide energy and charge (μ + versus μ − ) information. An electron in the detector produces an electromagnetic shower which can be distinguished from hadronic showers if the granularity of the active detector is small compared to the physical extent of the shower. Tau leptons decay essentially immediately to either pions or another charged lepton, and can't be observed directly in this kind of detector. (To directly observe taus, one typically looks for a kink in tracks in photographic emulsion.)
Most neutrino experiments must address the flux of cosmic rays that bombard the earth's surface. The higher energy (>50 MeV or so) neutrino experiments often cover or surround the primary detector with a "veto" detector which reveals when a cosmic ray passes into the primary detector, allowing the corresponding activity in the primary detector to be ignored ("vetoed"). For lower energy experiments, the cosmic rays are not directly the problem. Instead, the spallation neutrons and radioisotopes produced by the cosmic rays may mimic the desired physics signals. For these experiments, the solution is to locate the detector deep underground so that the earth above can reduce the cosmic ray rate to tolerable levels.
Some neutrino detectors are:
Antarctic Muon And Neutrino Detector Array
Project DUMAND
Super-Kamiokande
KamLAND
LSND
MiniBooNE
SNO
IceCube Neutrino Detector
MINOS
[edit]
Motivation for scientific interest in the neutrino
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 are very weakly interacting and therefore pass right through the sun with few or no interactions. While photons emitted by the solar core may require 1,000 years to diffuse to the outer layers of the Sun, neutrinos are virtually unimpeded and cross this distance at nearly the speed of light.
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 fast-moving protons and atomic nuclei, are not able to travel more than about 100 megaparsecs due to the GZK cutoff. Neutrinos can travel this distance, and greater distances, with very little attenuation.
The galactic core of the Milky Way is completely obscured by dense gas and numerous bright objects. However, it is likely that neutrinos produced in the galactic core will be measurable by Earth-based neutrino telescopes in the next decade.
The most 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 rapid (10 second) burst of neutrinos. As a result, the usefulness of neutrinos as a probe for this important event in the death of a star cannot be overstated.
Determining the mass of the neutrino (see above) is also an important test of cosmology (see dark matter). Many other important uses of the neutrino may be imagined in the future. It is clear that 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 taon generations of particles, that a fourth generation neutrino would be the easiest to generate in a particle accelerator.
Neutrinos are also obvious candidates for use in studying quantum gravity effects. Because they are not affected by either the strong interaction or electromagnetism, 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 is easier to isolate and measure gravitational effects on neutrinos at a quantum level.
[edit]
See also
Neutrino astronomy
Solar neutrino problem
Neutrino oscillation
Particle physics
List of particles
Neutrino Factory
neutrino physicists
Clyde Cowan
Raymond Davis Jr.
Riccardo Giacconi
Masatoshi Koshiba
Leon Lederman
Wolfgang Pauli
Martin Lewis Perl
Frederick Reines
Melvin Schwartz
Jack Steinberger
[edit]
References
Super-Kamiokande. Super-Kamiokande at UC Irvine. URL accessed on July 14, 2003.
Bahcall, John N. (1989). Neutrino Astrophysics. Cambridge University Press. ISBN 0521351138.
Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0471603864.
Perkins, Donald H. (1999). Introduction to High Energy Physics. Cambridge University Press. ISBN 0521621968.
Tipler, Paul; Llewellyn, Ralph (2002). Modern Physics (4th ed.). W. H. Freeman. ISBN 0716743450.
R. N. Mohapatra et al. (APS neutrino theory working group) (2005). "Theory of neutrinos: a white paper". preprint. arXiv:hep-ph/0510213
A. Goobar, S. Hannestad, E. Mörtsell and H. Tu (2006). "A new bound on the neutrino mass from the SDSS baryon acoustic peak". preprint. arXiv:astro-ph/0602155
[edit]
External links
The Neutrino Oscillatio
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Neutrino to cząstka elementarna, należąca do leptonów (fermionów o spinie 1/2). Ma zerowy ładunek elektryczny. Neutrina występują jako cząstki podstawowe w Modelu Standardowym. Doświadczenia przeprowadzone w ostatnich latach wskazują, że neutrina mają niewielką, ale bliską zeru masę. Powstają m.in. w wyniku rozpadu β+ neutronu atomu trytu (izotop wodoru) na proton, pozyton i ostatnią cząstkę uwalnianą podczas tego rozpadu - neutrino elektronowe:
Wyróżniamy 3 rodzaje neutrin:
elektronowe
mionowe
taonowe
Każdy rodzaj neutrina ma swój odpowiednik (antyneutrino) w antymaterii.
Neutrina, podczas propagacji w przestrzeni, mogą zmieniać swój rodzaj (zapach) - zjawisko to nazywamy oscylacją neutrin.
Neutrina nie oddziaływują za pomocą oddziaływań silnych i elektromagnetycznych. Oddziałują jedynie za pośrednictwem oddziaływań słabych (i grawitacyjnych). Są tak przenikliwe, że obiekt wielkości planety nie stanowi dla nich prawie żadnej przeszkody (przez Ziemię w każdej sekundzie przelatuje wiele bilionów neutrin).
Głównym źródłem neutrin na Ziemi są oddziaływania promieni kosmicznych w górnych warstwach atmosfery (powstające w ten sposób neutrina nazywamy atmosferycznymi). Neutrina emitowane są także przez Słońce (neutrina słoneczne) i inne źródła kosmiczne. Ze źródeł sztucznych najwięcej neutrin powstaje w reaktorach jądrowych.
Neutrina są wychwytywane przez jądro atomowe (przekrój czynny na ten proces jest bardzo mały) inicjując ich rozpad. Zjawisko to wykorzystuje się do wykrywania neutrin. Neutrina wychwytuje się w gigantycznych basenach z destylowaną wodą (bądź innymi substancjami) umieszczonych głęboko pod ziemią i obserwuje się powstałe w wyniku tego promieniowanie.
Ostatnimi laty nastąpił olbrzymi rozwój fizyki neutrin dzięki takim eksperymentom jak KamLand, Kamiokande, Super-Kamiokande, SNO, K2K i MINOS.
Zobacz też: Problem neutrin słonecznych
[Edytuj]
Linki zewnętrzne
Successful Observation of the Oscillatory Pattern of Neutrino Mixing
NuMI-MINOS Home Page
Neutrino physics at Fermilab
The Story of the Neutrino
Neutrino Unbound
Warszawska Grupa Neutrinowa
Wrocławska Grupa Neutrinowa
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Last week the dog, Ross's dog , took a study trip to Asia.
He seemed rather enamoured with some Pekinese pup.
出典: フリー百科事典『ウィキペディア（Wikipedia）』
ニュートリノ (Neutrino) は、素粒子の内のレプトンの一つ。中性微子とも書く。
標準モデルにおける
ニュートリノの分類
フェルミオン 記号 質量**
第一世代
電子ニュートリノ < 2.5 eV
反電子ニュートリノ < 2.5 eV
第二世代
ミューニュートリノ < 170 keV
反ミューニュートリノ < 170 keV
第三世代
タウニュートリノ < 18 MeV
反タウニュートリノ < 18 MeV
目次
[非表示]
1 性質
1.1 相互作用
2 発見と検証
2.1 質量
3 関連項目
4 外部リンク
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性質
ニュートリノは電荷を持たず、1/2のスピンを持つ。 また質量は非常に小さいが存在することが確認された。
ニュートリノには電子ニュートリノ (νe) 、ミューニュートリノ (νμ) 、タウニュートリノ (ντ) の3世代とそれぞれの反粒子が存在する。 これらは電子、ミュー粒子、タウ粒子と対をなしている。
[編集]
相互作用
ニュートリノは強い相互作用と電磁相互作用がなく、弱い相互作用と重力相互作用でしか反応しない。 ただ、質量が非常に小さいため、重力相互作用もほとんど反応せず、このため他の素粒子との反応がわずかで、透過性が非常に高い。
そのため、原子核や電子との衝突を利用した観測が難しく、ごく稀にしかない反応を捉えるために高感度のセンサや大質量の反応材料を用意する必要があり、他の粒子に比べ研究の進みは遅かった。
最初の写真 米国アルゴンヌ国立研究所に設置されたZero Gradient Synchrotronの水素泡箱で観測された史上初のニュートリノ（1970年11月13日）。ニュートリノは電荷を持たず泡箱に軌跡を残さない。写真右手中央の黒い影の右側で三つの軌跡が突然始っている。この位置でニュートリノが陽子に衝突した。同時に生成したミュー粒子は非常に見分けにくいがほぼ直線状に軌跡を残している。短い軌跡は陽子。
[編集]
発見と検証
アルファ崩壊の場合、アルファ粒子（アルファ線）と新しく出来た原子核の質量との合計は、崩壊前の原子核の質量よりも小さくなる。これは、放出されたアルファ粒子の運動エネルギーが、崩壊前の原子核の質量から得られているためである。
ベータ崩壊の場合は、運動エネルギーの増加が質量の減少より小さかったため、1931年、ヴォルフガング・パウリは、ベータ崩壊では中性の粒子がエネルギーを持ち去っている、と仮定した。
さらに1932年に中性子が発見されたのをきっかけに、フェルミはベータ崩壊のプロセスを「ベータ崩壊は原子核内の中性子が陽子と電子を放出しさらに中性の粒子も放出する」とした。そして質量は非常に小さいか、もしくはゼロと考えられた。そのため、他の物質と作用することがほとんどなく検出には困難を極めた。
1953年から1959年にかけて行われた F. Reines と C. L. Cowan の実験により初めてニュートリノが観測された。この実験では、原子炉から生じたニュートリノビームを水にあて、水分子中の原子核とニュートリノが反応することにより生じる中性子と陽電子を観測することで、ニュートリノの存在を証明した。
1962年、L. Lederman, M. Schwarts, J. Steinberger らによって νe と νμ が違う粒子であることが実験で確認された。これは、15GeV の高エネルギー陽子ビームを使ってパイ中間子(π)をつくり、ミュー粒子 (μ) とミューニュートリノ (νμ) に崩壊してできたニューニュートリノを標的にあてた。この結果、標的で弱い相互作用によってミュー粒子は生じたが、電子は生成されなかった。
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質量
ニュートリノが質量を持つとすると、量子状態の混在がありえるため、ニュートリノが電子・ミュー・タウの型の間で変化するニュートリノ振動とよばれる現象が予言されていた。
この現象について、1998年6月にスーパーカミオカンデ共同実験グループは、宇宙線が大気と衝突する際に発生する大気ニュートリノの観測から、ニュートリノ振動の証拠を99%の確度で確認した。 また、2001年には、太陽からくる太陽ニュートリノの観察からも強い証拠を得た。
その後、つくば市にあるKEKからスーパーカミオカンデに向かってニュートリノを発射するK2Kの実験において、ニュートリノの存在確率が変動している状態を直接的に確認し、2004年、質量があることを確実なものとした。
ニュートリノの質量が問題になるのは、2004年の時点で広く知られている標準理論やその拡張の多くが、ニュートリノの質量が 0 であることを前提としているためである。 このため質量があるとすると大幅な理論の再検討を促すことになる。
また相互作用の少なさから、熱い暗黒物質の候補のひとつではあったが、質量があることが確認されたことから、この候補がしぼられることになった。
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関連項目
ニュートリノ天文学
超新星爆発
物理学
小柴昌俊
[編集]
外部リンク
つくば・神岡間長基線ニュートリノ振動実験 (K2K) 公式サイト
大強度陽子加速器を用いた次期ニュートリノ振動実験計画
この「ニュートリノ」は、自然科学に関連した書きかけ項目です。この記事を加筆・訂正などして下さる協力者を求めています。
カテゴリ: 自然科学関連のスタブ項目 | 素粒子
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最終更新 2006年4月3日 (月) 21:40。
Text is available under GNU Free Documentation License.
プライバシー・ポリシー
Wikipediaについて
免責事項
G&L's dog couldnt candle this canine could he? Could she I mean?
In simple English:
Neutrino
From Wikipedia, a free encyclopedia written in simple English for easy reading.
A neutrino is a type of elementary particle studied by physicists. They are very hard to find because they are so small, they almost don't interact with regular matter.
And our dog, she says, Ross's dog may think he's a smartie britches, writing Chinese and knowing all about complex things like MiniBooNE and the ice cube neutrino detector, but he's simply missed the most fundamental and significant neutrino ever discovered in doggy universe, aptly named the Large Shank Bone Neutrino (a name to rival the human Tau and Muon Neutrinos). She goes on, humans think they're really very clever giving names to fundamental particles like Strange and Charm Quarks, even Up and Down ones, and in doggy-speak the height of fundamental cleverness is attained in the discovery and naming of the LSBN (which incidentally, was detected in a full doggy bowl, which in itself is a rare occurrence). It has never been detected by humans, but may one day yet when some human investigates the sublime yet fleeting delights of the full doggy bowl.
And with that wisdom, she curled up on her warm furry mat and is now stretched out asleep in doggy dreamland.
Well Geoff I ran it past the dog, Ross's dog. He said well Shadow would do that, the only way Shadow would find the LSBN neutrino in her bowl is if it were already depleted. A full on neutrino would even pass right through the sun at just under the speed of light. So how can it be just lying around for any old shadow to find ? ( Pun on Sun I think)
The dog figures what you really have is not a massless particle but an energyless particle
( E=0) = mc2
= 0
And thats really good, if you can find a market for them.
The dog said Shadow might do well in research into Womens Intuition and Mothers Know Everything Syndromes, being a woman and a possible dogstein...
Really amazing! Useful information. All the best.
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I love your website. It has a lot of great pictures and is very informative.
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