IceCube Neutrino Detector
Encyclopedia
The IceCube Neutrino Observatory (or simply IceCube) is a neutrino telescope constructed at the Amundsen-Scott South Pole Station
in Antarctica. Similar to its predecessor, the Antarctic Muon And Neutrino Detector Array
(AMANDA), IceCube contains thousands of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT)
and a single board data acquisition computer which sends digital data to the counting house on the surface above the array.
IceCube was completed on 18 December, 2010, New Zealand time.
DOMs are deployed on "strings" of sixty modules each at depths ranging from 1,450 to 2,450 meters, into holes melted in the ice using a hot water drill. IceCube is designed to look for point sources of neutrino
s in the TeV
range to explore the highest-energy astrophysical processes.
projects developed and supervised by the same institution, while collaboration and funding is provided by numerous other universities and research institutions worldwide. Construction of IceCube is only possible during the Antarctic austral summer from November to February, when permanent sunlight allows for 24 hour drilling. Construction began in 2005, when the first IceCube string was deployed and collected enough data to verify that the optical sensors worked correctly. In the 2005–2006 season, an additional eight strings were deployed, making IceCube the largest neutrino telescope in the world.
Construction was completed on 17 December 2010.
lepton
s, and interact very rarely with matter. When they do react with the molecules of water in the ice, they can create charged leptons (electron
s, muon
s, or tau
s). These charged leptons can, if they are energetic enough, emit Cherenkov radiation
. This happens when the charged particle travels through the ice faster than the speed of light
in the ice, similar to the bow shock
of a boat traveling faster than the waves it crosses. This light can then be detected by photomultiplier tube
s within the digital optical modules making up IceCube.
The signals from the PMTs are digitized and then sent to the surface of the glacier on a cable. These signals are collected in a surface counting house, and some of them are sent north via satellite for further analysis. More of the data is kept on tape and sent north once a year via ship. Once the data reach experimenters, they can reconstruct kinematical parameters of the incoming neutrino. High-energy neutrinos may leave a large signal in the detector, pointing back to their origin. Clusters of such neutrino directions indicate point sources of neutrinos.
Each of the above steps requires a certain minimum energy, and thus IceCube is sensitive mostly to high energy neutrinos, in the range of 1011 to about 1021 eV
. Estimates predict a neutrino event about every 20 minutes in the fully constructed IceCube detector.
IceCube is more sensitive to muon
s than other charged leptons, because they are the most penetrating and thus have the longest tracks in the detector. Thus, of the neutrino flavors, IceCube is most sensitive to muon neutrino
s. Electron neutrino
s typically scatter
several times before losing enough energy to fall below the Cherenkov threshold; this means that they cannot typically be used to point back to sources, but they are more likely to be fully contained in the detector, and thus they can be useful for energy studies. These events are more spherical, or "cascade"-like, than "track"-like; muon neutrinos are more track-like.
Tau
s can also create cascade events; but are short-lived and cannot travel very far before decaying, and are thus usually indistinguishable from electron cascades. A tau could be distinguished from an electron with a "double bang" event, where a cascade is seen both at the tau creation and decay. This is only possible with very high energy taus. Hypothetically, to resolve a tau track, the tau would need to travel at least from one DOM to an adjacent DOM (17 m) before decaying. As the average lifetime of a tau is , a tau traveling at near the speed of light would require 20 TeV of energy for every meter traveled. Realistically, an experimenter would need more space than just one DOM to the next to distinguish two cascades, so double bang searches are centered at PeV
scale energies. Such searches are under way but have not so far isolated a double bang event from background events.
However, there is a large background
of muons created not by neutrinos from astrophysical sources but by cosmic rays impacting the atmosphere
above the detector. There are about 106 times more cosmic ray muons than neutrino-induced muons observed in IceCube. Most of these can be rejected using the fact that they are traveling downwards. Most of the remaining (up-going) events are from neutrinos, but most of these neutrinos are from cosmic rays hitting the far side of the Earth; some unknown fraction may come from astronomical sources, and these neutrinos are the key to IceCube point source searches. Estimates predict the detection of about 75 upgoing neutrinos per day in the fully constructed IceCube detector. The arrival directions of these astrophysical neutrinos are the points with which the IceCube telescope maps the sky. To distinguish these two types of neutrinos statistically, the direction and energy of the incoming neutrino is estimated from its collision by-products. Unexpected excesses in energy or excesses from a given spatial direction indicate an extraterrestrial source.
(an array of Cherenkov detecting tanks) than it is to other neutrino experiments, such as Super-K (with inward-facing PMTs fixing the fiducial volume).
IceCube is sensitive to point sources more in the northern hemisphere than the southern. It can observe astrophysical neutrino signals from any direction, but in the southern hemisphere these neutrinos are swamped by the downgoing cosmic-ray muon background. Thus, early IceCube point source searches focus on the northern hemisphere, and the extension to southern hemisphere point sources takes extra work.
Although IceCube is expected to detect very few neutrinos (relative to the number of photons detected by more traditional telescopes), it should have very high resolution with the ones that it does find. Over several years of operation, it could produce a flux map of the northern hemisphere similar to existing maps like that of the cosmic microwave background, or gamma ray telescopes, which use particle terminology more like IceCube. Likewise, KM3NeT
could complete the map for the southern hemisphere.
IceCube scientists detected their first neutrinos on January 29, 2006.
s collide with one another or with photon
s, the result is usually pion
s. Charged pions decay into muon
s and muon neutrino
s whereas neutral pions decay into gamma rays. Potentially, the neutrino flux and the gamma ray flux may coincide in certain sources such as gamma ray burst
s and supernova remnant
s, indicating the elusive nature of their origin. Data from IceCube is being used in conjunction with cosmic ray detectors like HESS
or MAGIC
for this goal. The 22 string setup, "IC22," did not observe any neutrinos in coincidence with GRBs, but was able to use this search to constrain neutrino flux models from GRBs.
could be attracted by the mass of the Sun
and collect gravitationally in the core of the Sun
. With a high enough density of these particles, they would annihilate
with each other at a significant rate. The decay products of this annihilation could decay into neutrinos, which could be observed by IceCube as an excess of neutrinos from the direction of the Sun. This technique of looking for the decay products of WIMP annihilation is called indirect, as opposed to direct searches which look for dark matter interacting within a contained, instrumented volume. Solar WIMP searches are more sensitive to spin
-dependent WIMP models than many direct searches, because the Sun is made of lighter elements than direct search detectors (e.g. xenon
or germanium
). IceCube has set better limits with the 22 string detector (about of the full detector) than the AMANDA limits.
s from atmospheric cosmic ray showers, over a baseline across the Earth. It is most sensitive at ~25 GeV, the energy range which Deep Core will be able to see. IceCube can constrain θ23. Deep Core will have the full 6 strings deployed by the end of the 2009–2010 austral summer. As more data is collected and IceCube can refine this measurement, it may be possible to observe a shift in the oscillation peak that determines the neutrino mass hierarchy. This mechanism for determining the mass hierarchy would only work if θ13 is sufficiently large (close to present limits).
(SNEWS).
s predicted in string theory
. Many extensions of the Standard Model of particle physics, including string theory, propose a sterile neutrino
; in string theory this is made from a closed string. These could leak into extra dimensions before returning, making them appear to travel faster than the speed of light. An experiment to test this may be possible in the near future. Furthermore, if high energy neutrinos create microscopic black hole
s (as predicted by some aspects of string theory) it would create a shower of particles; resulting in an increase of "down" neutrinos while reducing "up" neutrinos. There is no group within the IceCube collaboration working on tachyons, travel through extra dimensions, or observations of microscopic black holes.
annihilation in the Sun, with implications for WIMP-proton
cross section
s. A shadowing effect from the Moon has been observed. Cosmic ray protons are blocked by the Moon, creating a deficit of cosmic ray shower muons in the direction of the Moon. A small (under 1%) but robust anisotropy
has been observed in cosmic ray muons.
Amundsen-Scott South Pole Station
The Amundsen–Scott South Pole Station is the American scientific research station on the high plateau of Antarctica. This station is located at the southernmost place on the Earth, the Geographic South Pole, at an elevation of 2,835 meters above sea level.The original Amundsen-Scott Station was...
in Antarctica. Similar to its predecessor, the Antarctic Muon And Neutrino Detector Array
Antarctic Muon And Neutrino Detector Array
The Antarctic Muon And Neutrino Detector Array is a neutrino telescope located beneath the Amundsen-Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of its successor project, the IceCube Neutrino Observatory.AMANDA consists of optical modules, each...
(AMANDA), IceCube contains thousands of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT)
and a single board data acquisition computer which sends digital data to the counting house on the surface above the array.
IceCube was completed on 18 December, 2010, New Zealand time.
DOMs are deployed on "strings" of sixty modules each at depths ranging from 1,450 to 2,450 meters, into holes melted in the ice using a hot water drill. IceCube is designed to look for point sources of neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
s in the TeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
range to explore the highest-energy astrophysical processes.
Construction status
The IceCube project is part of the University of Wisconsin–MadisonUniversity of Wisconsin–Madison
The University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...
projects developed and supervised by the same institution, while collaboration and funding is provided by numerous other universities and research institutions worldwide. Construction of IceCube is only possible during the Antarctic austral summer from November to February, when permanent sunlight allows for 24 hour drilling. Construction began in 2005, when the first IceCube string was deployed and collected enough data to verify that the optical sensors worked correctly. In the 2005–2006 season, an additional eight strings were deployed, making IceCube the largest neutrino telescope in the world.
| Season | # Strings Installed | Total # Strings |
|---|---|---|
| 2005 | 1 | 1 |
| 2005–2006 | 8 | 9 |
| 2006–2007 | 13 | 22 |
| 2007–2008 | 18 | 40 |
| 2008–2009 | 19 | 59 |
| 2009–2010 | 20 | 79 |
| 2010–2011 | 7 | 86 |
Construction was completed on 17 December 2010.
Sub-detectors
The IceCube Neutrino Observatory is made up of several sub-detectors in addition to the main in-ice array.- AMANDA, the Antarctic Muon And Neutrino Detector ArrayAntarctic Muon And Neutrino Detector ArrayThe Antarctic Muon And Neutrino Detector Array is a neutrino telescope located beneath the Amundsen-Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of its successor project, the IceCube Neutrino Observatory.AMANDA consists of optical modules, each...
, was the first part built, and it served as a proof-of-concept for IceCube. AMANDA was turned off in April 2009. - The IceTop array is a series of Cherenkov detectorCherenkov detectorA Cherenkov detector is a particle detector using the mass-dependent threshold energy of Cherenkov radiation. This allows a discrimination between a lighter particle and a heavier particle ....
s on the surface of the glacier, two detectors approximately above each IceCube string. IceTop is used as a cosmic ray shower detector, for cosmic ray composition studies and coincident event tests: if a muonMuonThe muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
is observed going through IceTop, it cannot be from a neutrino interacting in the ice. - The Deep Core Low-Energy Extension is a densely instrumented region of the IceCube array which extends the observable energies below 100 GeVElectronvoltIn physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
. The Deep Core strings are deployed at the center (in the surface plane) of the larger array, deep in the clearest ice at the bottom of the array (between 1760 and 2450 m deep). There are no Deep Core DOMs between 1850 m and 2107 m depth, as the ice is not as clear in those layers.
Experimental mechanism
Neutrinos are electrically neutralElectric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
lepton
Lepton
A lepton is an elementary particle and a fundamental constituent of matter. The best known of all leptons is the electron which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons , and neutral...
s, and interact very rarely with matter. When they do react with the molecules of water in the ice, they can create charged leptons (electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s, or tau
Tau lepton
The tau , also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton...
s). These charged leptons can, if they are energetic enough, emit Cherenkov radiation
Cherenkov radiation
Cherenkov radiation is electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium...
. This happens when the charged particle travels through the ice faster than the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
in the ice, similar to the bow shock
Bow shock
A bow shock is the area between a magnetosphere and an ambient medium. For stars, this is typically the boundary between their stellar wind and the interstellar medium....
of a boat traveling faster than the waves it crosses. This light can then be detected by photomultiplier tube
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
s within the digital optical modules making up IceCube.
The signals from the PMTs are digitized and then sent to the surface of the glacier on a cable. These signals are collected in a surface counting house, and some of them are sent north via satellite for further analysis. More of the data is kept on tape and sent north once a year via ship. Once the data reach experimenters, they can reconstruct kinematical parameters of the incoming neutrino. High-energy neutrinos may leave a large signal in the detector, pointing back to their origin. Clusters of such neutrino directions indicate point sources of neutrinos.
Each of the above steps requires a certain minimum energy, and thus IceCube is sensitive mostly to high energy neutrinos, in the range of 1011 to about 1021 eV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
. Estimates predict a neutrino event about every 20 minutes in the fully constructed IceCube detector.
IceCube is more sensitive to muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s than other charged leptons, because they are the most penetrating and thus have the longest tracks in the detector. Thus, of the neutrino flavors, IceCube is most sensitive to muon neutrino
Muon neutrino
The muon neutrino is a subatomic lepton elementary particle which has the symbol and no net electric charge. Together with the muon it forms the second generation of leptons, hence its name muon neutrino. It was first hypothesized in the early 1940s by several people, and was discovered in 1962 by...
s. Electron neutrino
Electron neutrino
The electron neutrino is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino...
s typically scatter
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
several times before losing enough energy to fall below the Cherenkov threshold; this means that they cannot typically be used to point back to sources, but they are more likely to be fully contained in the detector, and thus they can be useful for energy studies. These events are more spherical, or "cascade"-like, than "track"-like; muon neutrinos are more track-like.
Tau
Tau lepton
The tau , also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton...
s can also create cascade events; but are short-lived and cannot travel very far before decaying, and are thus usually indistinguishable from electron cascades. A tau could be distinguished from an electron with a "double bang" event, where a cascade is seen both at the tau creation and decay. This is only possible with very high energy taus. Hypothetically, to resolve a tau track, the tau would need to travel at least from one DOM to an adjacent DOM (17 m) before decaying. As the average lifetime of a tau is , a tau traveling at near the speed of light would require 20 TeV of energy for every meter traveled. Realistically, an experimenter would need more space than just one DOM to the next to distinguish two cascades, so double bang searches are centered at PeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
scale energies. Such searches are under way but have not so far isolated a double bang event from background events.
However, there is a large background
Background noise
In acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...
of muons created not by neutrinos from astrophysical sources but by cosmic rays impacting the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
above the detector. There are about 106 times more cosmic ray muons than neutrino-induced muons observed in IceCube. Most of these can be rejected using the fact that they are traveling downwards. Most of the remaining (up-going) events are from neutrinos, but most of these neutrinos are from cosmic rays hitting the far side of the Earth; some unknown fraction may come from astronomical sources, and these neutrinos are the key to IceCube point source searches. Estimates predict the detection of about 75 upgoing neutrinos per day in the fully constructed IceCube detector. The arrival directions of these astrophysical neutrinos are the points with which the IceCube telescope maps the sky. To distinguish these two types of neutrinos statistically, the direction and energy of the incoming neutrino is estimated from its collision by-products. Unexpected excesses in energy or excesses from a given spatial direction indicate an extraterrestrial source.
Point sources of high energy neutrinos
A point source of neutrinos could help explain the mystery of the origin of the highest energy cosmic rays. These cosmic rays have energies high enough that they cannot be contained by galactic magnetic fields (their gyroradii are larger than the radius of the galaxy), so they are believed to come from extra-galactic sources. Astrophysical events which are cataclysmic enough to create such high energy particles would probably also create high energy neutrinos, which could travel to the Earth with very little deflection, because neutrinos interact so rarely. IceCube could observe these neutrinos: its observable energy range is about 100 GeV to several PeV. The more energetic an event is, the larger volume IceCube may detect it in; in this sense, IceCube is more similar to Cherenkov telescopes like the Pierre Auger ObservatoryPierre Auger Observatory
The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles with energies beyond 1020 eV...
(an array of Cherenkov detecting tanks) than it is to other neutrino experiments, such as Super-K (with inward-facing PMTs fixing the fiducial volume).
IceCube is sensitive to point sources more in the northern hemisphere than the southern. It can observe astrophysical neutrino signals from any direction, but in the southern hemisphere these neutrinos are swamped by the downgoing cosmic-ray muon background. Thus, early IceCube point source searches focus on the northern hemisphere, and the extension to southern hemisphere point sources takes extra work.
Although IceCube is expected to detect very few neutrinos (relative to the number of photons detected by more traditional telescopes), it should have very high resolution with the ones that it does find. Over several years of operation, it could produce a flux map of the northern hemisphere similar to existing maps like that of the cosmic microwave background, or gamma ray telescopes, which use particle terminology more like IceCube. Likewise, KM3NeT
Km3net
KM3NeT, an acronym for Cubic Kilometre Neutrino Telescope, is a future European research infrastructure which will be located at the bottom of the Mediterranean Sea...
could complete the map for the southern hemisphere.
IceCube scientists detected their first neutrinos on January 29, 2006.
Gamma ray bursts coincident with neutrinos
When protonProton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s collide with one another or with photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s, the result is usually pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s. Charged pions decay into muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s and muon neutrino
Muon neutrino
The muon neutrino is a subatomic lepton elementary particle which has the symbol and no net electric charge. Together with the muon it forms the second generation of leptons, hence its name muon neutrino. It was first hypothesized in the early 1940s by several people, and was discovered in 1962 by...
s whereas neutral pions decay into gamma rays. Potentially, the neutrino flux and the gamma ray flux may coincide in certain sources such as gamma ray burst
Gamma ray burst
Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
s and supernova remnant
Supernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
s, indicating the elusive nature of their origin. Data from IceCube is being used in conjunction with cosmic ray detectors like HESS
Hess
Hess or Heß may refer to:* People with the surname Hess * Hess Educational Organization, the largest private provider of English instruction in the Republic of China...
or MAGIC
MAGIC (telescope)
MAGIC is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, at about 2200 m above sea level...
for this goal. The 22 string setup, "IC22," did not observe any neutrinos in coincidence with GRBs, but was able to use this search to constrain neutrino flux models from GRBs.
Indirect dark matter searches
Weakly interacting massive particle (WIMP) dark matterDark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
could be attracted by the mass of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and collect gravitationally in the core of the Sun
Solar core
The core of the Sun is considered to extend from the center to about 0.2 to 0.25 solar radius. It is the hottest part of the Sun and of the Solar System. It has a density of up to 150 g/cm³ and a temperature of close to 15,000,000 kelvin...
. With a high enough density of these particles, they would annihilate
Annihilation
Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
with each other at a significant rate. The decay products of this annihilation could decay into neutrinos, which could be observed by IceCube as an excess of neutrinos from the direction of the Sun. This technique of looking for the decay products of WIMP annihilation is called indirect, as opposed to direct searches which look for dark matter interacting within a contained, instrumented volume. Solar WIMP searches are more sensitive to spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
-dependent WIMP models than many direct searches, because the Sun is made of lighter elements than direct search detectors (e.g. xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
or germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
). IceCube has set better limits with the 22 string detector (about of the full detector) than the AMANDA limits.
Neutrino oscillations
IceCube can observe neutrino oscillationNeutrino oscillation
Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvowhereby a neutrino created with a specific lepton flavor can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates...
s from atmospheric cosmic ray showers, over a baseline across the Earth. It is most sensitive at ~25 GeV, the energy range which Deep Core will be able to see. IceCube can constrain θ23. Deep Core will have the full 6 strings deployed by the end of the 2009–2010 austral summer. As more data is collected and IceCube can refine this measurement, it may be possible to observe a shift in the oscillation peak that determines the neutrino mass hierarchy. This mechanism for determining the mass hierarchy would only work if θ13 is sufficiently large (close to present limits).
Galactic supernovae
Despite the fact that individual neutrinos expected from supernovae have energies well below the IceCube energy cutoff, IceCube could detect a local supernova. It would appear as a detector-wide, brief, correlated rise in noise rates. The supernova would have to be relatively close (within our galaxy) to get enough neutrinos before the 1/r2 distance dependence took over. IceCube is a member of the Supernova Early Warning SystemSupernova Early Warning System
The SuperNova Early Warning System is a network of neutrino detectors designed to give early warning to astronomers in the event of a supernova in the Milky Way galaxy or a nearby galaxy such as the Large Magellanic Cloud or the Canis Major Dwarf Galaxy. Enormous numbers of neutrinos are produced...
(SNEWS).
String theory
The described detection strategy, along with its South Pole position, could allow the detector to provide the first robust experimental evidence of extra dimensionSuperstring theory
Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modelling them as vibrations of tiny supersymmetric strings...
s predicted in string theory
String theory
String theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything , a manner of describing the known fundamental forces and matter in a mathematically complete system...
. Many extensions of the Standard Model of particle physics, including string theory, propose a sterile neutrino
Sterile neutrino
Sterile neutrinosIn scientific literature, these particles are also variously referred to as right-handed neutrinos, inert neutrinos, heavy neutrinos, or neutral heavy leptons . are a hypothetical type of neutrino that do not interact via any of the fundamental interactions of the Standard Model...
; in string theory this is made from a closed string. These could leak into extra dimensions before returning, making them appear to travel faster than the speed of light. An experiment to test this may be possible in the near future. Furthermore, if high energy neutrinos create microscopic black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
s (as predicted by some aspects of string theory) it would create a shower of particles; resulting in an increase of "down" neutrinos while reducing "up" neutrinos. There is no group within the IceCube collaboration working on tachyons, travel through extra dimensions, or observations of microscopic black holes.
Results
The IceCube collaboration has published flux limits for neutrinos from point sources, Gamma-ray bursts, and neutralinoNeutralino
In particle physics, the neutralino is a hypothetical particle predicted by supersymmetry. There are four neutralinos that are fermions and are electrically neutral, the lightest of which is typically stable...
annihilation in the Sun, with implications for WIMP-proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
cross section
Cross section (physics)
A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer-Lambert law....
s. A shadowing effect from the Moon has been observed. Cosmic ray protons are blocked by the Moon, creating a deficit of cosmic ray shower muons in the direction of the Moon. A small (under 1%) but robust anisotropy
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
has been observed in cosmic ray muons.
See also
- Deep Core Low-Energy Extension of IceCube
- Antarctic Muon And Neutrino Detector ArrayAntarctic Muon And Neutrino Detector ArrayThe Antarctic Muon And Neutrino Detector Array is a neutrino telescope located beneath the Amundsen-Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of its successor project, the IceCube Neutrino Observatory.AMANDA consists of optical modules, each...
- Radio Ice Cerenkov ExperimentRadio Ice Cerenkov ExperimentRadio Ice Cerenkov Experiment is an experiment designed to detect the Cherenkov emission in the radio regime of the electromagnetic spectrum from the interaction of high energy neutrinos with the Antarctic ice cap...
- ANTARESANTARES (telescope)ANTARES is the name of a neutrino detector residing 2.5 km under the Mediterranean Sea off the coast of Toulon, France. It is designed to be used as a directional Neutrino Telescope to locate and observe neutrino flux from cosmic origins in the direction of the Southern Hemisphere of the...
and KM3NeTKm3netKM3NeT, an acronym for Cubic Kilometre Neutrino Telescope, is a future European research infrastructure which will be located at the bottom of the Mediterranean Sea...
, similar neutrino telescopes using deep-sea water instead of ice.