IceCube Neutrino Observatory
Alternative names | IceCube Laboratory | ||
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Organization | IceCube collaboration | ||
Location | Amundsen–Scott South Pole Station | ||
Coordinates | 89°59′24″S 63°27′11″W / 89.99000°S 63.45306°W | ||
Website | icecube | ||
Telescopes | |||
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Related media on Commons | |||
The IceCube Neutrino Observatory (or simply IceCube) is a
Similar to its predecessor, the Antarctic Muon And Neutrino Detector Array (AMANDA), IceCube consists of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT)[4] and a single-board data acquisition computer which sends digital data to the counting house on the surface above the array.[5] IceCube was completed on 18 December 2010.[6]
DOMs are deployed on strings of 60 modules each at depths between 1,450 and 2,450 meters into holes melted in the ice using a hot water drill. IceCube is designed to look for point sources of neutrinos in the teraelectronvolt (TeV) range to explore the highest-energy astrophysical processes.
Construction
IceCube is part of a series of projects developed and supervised by the
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 | 7 | 86 |
Construction was completed on 17 December 2010.[9][10] The total cost of the project was $279 million.[11]
As of 2024, plans for further upgrades to the array are in the federal approval process.[12] If approved, the detectors for IceCube2 will each be eight times the size of those currently emplaced. The observatory will be able to detect more sources of particles, and discern their properties more finely at both lower and higher energy levels.[12]
Sub-detectors
The IceCube Neutrino Observatory is composed of several sub-detectors which is also in addition to the main in-ice array.
- AMANDA, the proof-of-concept for IceCube. AMANDA was turned off in May 2009.[13]
- The IceTop array is a series of coincident event tests: if a muonis 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 GeV. 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.
PINGU (Precision IceCube Next Generation Upgrade) is a proposed extension that will allow detection of low energy neutrinos (GeV energy scale), with uses including determining the neutrino mass hierarchy, precision measurement of atmospheric neutrino oscillation (both tau neutrino appearance and muon neutrino disappearance), and searching for
Experimental mechanism
Neutrinos are
The detector signatures of the three charged leptons are distinct, and as such it's possible to determine the neutrino flavor of charged current events. On the other hand if the neutrino scattered off the ice via the neutral current instead, the final state contains no information of the neutrino flavor since no charged lepton was created.
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. Since 2014, hard drives rather than tape store the balance of the data which is sent north once a year via ship. Once the data reaches experimenters, they can reconstruct
Each of the above steps requires a certain minimum energy, and thus IceCube is sensitive mostly to high-energy neutrinos, in the range of 107 to about 1021 eV.[16]
IceCube is more sensitive to muons 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
Tau leptons 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 2.9×10−13 s, a tau traveling at near the speed of light would require 20 TeV of energy for every meter traveled.[17] 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 underway but have not so far isolated a double bang event from background events.[18] Another way to detect lower energy tau neutrinos is through the "double pulse" signature, where a single DOM detect two distinct light arrival times corresponding to the neutrino interaction and tau decay vertices.[19] One can also use machine learning (ML) techniques, such as Convolutional Neural Networks, to distinguish the tau neutrino signal. In 2024 the IceCube collaboration published its findings of seven astrophysical tau neutrino candidates using such a technique.[20][21]
There is a large
Experimental goals
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
IceCube is more sensitive to point sources in the northern hemisphere than in the southern hemisphere. It can observe astrophysical neutrino signals from any direction, but neutrinos coming from the direction of the southern hemisphere are swamped by the 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.[22]
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
IceCube scientists may have detected their first neutrinos on 29 January 2006.[23]
Gamma-ray bursts coincident with neutrinos
When protons collide with one another or with photons, the result is usually pions. Charged pions decay into muons and muon neutrinos 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 bursts and supernova remnants, indicating the elusive nature of their origin. Data from IceCube is being used in conjunction with gamma-ray satellites like
Indirect dark matter searches
Weakly interacting massive particle (WIMP) dark matter could be gravitationally captured by massive objects like the Sun and accumulate 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 1⁄4 of the full detector) than the AMANDA limits.[25]
Neutrino oscillations
IceCube can observe
As more data is collected and IceCube measurements are refined further, it may be possible to observe the characteristic modification of the oscillation pattern at ~15 GeV that determines the neutrino
Galactic supernovae
Despite the fact that individual
Sterile neutrinos
A signature of sterile neutrinos would be a distortion of the energy spectrum of atmospheric neutrinos around 1 TeV, for which IceCube is uniquely positioned to search. This signature would arise from matter effects as atmospheric neutrinos interact with the matter of the Earth.
The described detection strategy, along with its South Pole position, could allow the detector to provide the first robust experimental evidence of
In 2016, scientists at the IceCube detector did not find any evidence for the sterile neutrino.[34]
Results
The IceCube collaboration has published flux limits for neutrinos from point sources,[35] gamma-ray bursts,[36] and neutralino annihilation in the Sun, with implications for WIMP–proton cross section.[37]
A shadowing effect from the Moon has been observed.[38][39] 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.[40]
In November 2013 it was announced that IceCube had detected 28 neutrinos that likely originated outside the Solar System and among those a pair of high energy neutrinos in the peta-electron volt range, making them the highest energy neutrinos discovered to date.[41] The pair were nicknamed "Bert" and "Ernie", after characters from the Sesame Street TV show.[42] Later in 2013 the number of detection increased to 37 candidates[43] including a new high energy neutrino at 2000-TeV given the name of "Big Bird".[44]
IceCube measured 10–100 GeV atmospheric muon neutrino disappearance in 2014, using three years of data taken May 2011 to April 2014, including DeepCore,[26] determining neutrino oscillation parameters ∆m232 = 2.72+0.19
−0.20 × 10−3 eV2 and sin2(θ23) = 0.53+0.09
−0.12 (normal mass hierarchy), comparable to other results. The measurement was improved using more data in 2017, and in 2019 atmospheric tau neutrino appearance was measured.[27][28] The latest measurement with improved detector calibration and data processing from 2023 has resulted in more precise values of the oscillation parameters, determining ∆m232 = (2.41 ± 0.07) × 10−3 eV2 and sin2(θ23) = 0.51 ± 0.05 (normal mass hierarchy).[29]
In July 2018, the IceCube Neutrino Observatory announced that they had traced an extremely-high-energy neutrino that hit their detector in September 2017 back to its point of origin in the
In 2020, evidence of the Glashow resonance at 2.3σ (formation of the W boson in antineutrino-electron collisions) was announced.[50]
In February 2021, the tidal disruption event (TDE) AT2019dsg was reported as candidate for a neutrino source[51][52] and the TDE AT2019fdr as a second candidate in June 2022.[53][54]
In November 2022, IceCube announced strong evidence of a neutrino source emitted by the
In June 2023 IceCube identified as a galactic map the neutrino diffuse emission from the Galactic plane at the 4.5σ level of significance.[58][59]
See also
- Antarctic Muon And Neutrino Detector Array
- Radio Ice Cherenkov Experiment
- ANTARES and KM3NeT, similar neutrino telescopes using deep-sea water instead of ice.
- Multimessenger astronomy
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External links
- Official website
- AMANDA at UCI
- IceCube expermint record on INSPIRE-HEP