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Kamioka Liquid Scintillator Antineutrino Detector

kamioka liquid scintillator antineutrino detectors
Coordinates: 36°25′21″N 137°18′55″E / 364225°N 1373153°E / 364225; 1373153[1]:105 The Kamioka Liquid Scintillator Antineutrino Detector KamLAND is an electron antineutrino detector at the Kamioka Observatory, an underground neutrino detection facility near Toyama, Japan The device is situated in a drift mine shaft in the old KamiokaNDE cavity in the Japanese Alps The site is surrounded by 53 Japanese commercial nuclear reactors Nuclear reactors produce electron antineutrinos ν ¯ e }_} during the decay of radioactive fission products in the nuclear fuel Like the intensity of light from a light bulb or a distant star, the isotropically-emitted ν ¯ e }_} flux decreases at 1/R2 per increasing distance R from the reactor The device is sensitive up to an estimated 25% of antineutrinos from nuclear reactors that exceed the threshold energy of 18 megaelectronvolts MeV and thus produces a signal in the detector

If neutrinos have mass, they may oscillate into flavors that an experiment may not detect, leading to a further dimming, or "disappearance," of the electron antineutrinos KamLAND is located at an average flux-weighted distance of approximately 180 kilometers from the reactors, which makes it sensitive to the mixing of neutrinos associated with large mixing angle LMA solutions to the solar neutrino problem

Contents

  • 1 KamLAND Detector
  • 2 Results
    • 21 Neutrino oscillation
    • 22 Geological antineutrinos geoneutrinos
    • 23 KamLAND-Zen Double Beta Decay Search
  • 3 References
  • 4 Further reading
  • 5 External links

KamLAND Detector

The KamLAND detector's outer layer consists of an 18 meter-diameter stainless steel containment vessel with an inner lining of 1,879 photo-multiplier tubes 1325 17" and 554 20" PMTs[2] Photocathode coverage is 34% Its second, inner layer consists of a 7001130000000000000♠13 m-diameter nylon balloon filled with a liquid scintillator composed of 1,000 metric tons of mineral oil, benzene, and fluorescent chemicals Non-scintillating, highly purified oil provides buoyancy for the balloon and acts as a buffer to keep the balloon away from the photo-multiplier tubes; the oil also shields against external radiation A 32 kiloton cylindrical water Cherenkov detector surrounds the containment vessel, acting as a muon veto counter and providing shielding from cosmic rays and radioactivity from the surrounding rock

Electron antineutrinos
ν
e are detected through the Inverse beta decay reaction ν ¯ e + p → e + + n }_+p\to e^+n} , which has a 18 MeV ν ¯ e }_} energy threshold The prompt scintillation light from the positron e + } gives an estimate of the incident antineutrino energy, E ν = E p r o m p t + < E n > + 09 M e V =E_+<E_>+09MeV} , where E p r o m p t } is the prompt event energy including the positron kinetic energy and the e + e − e^} annihilation energy The quantity < E n } > is the average neutron recoil energy, which is only a few tens of kiloelectronvolts keV The neutron is captured on hydrogen approximately 200 microseconds μs later, emitting a characteristic 6987352478827140000♠22 MeV
γ
ray This delayed-coincidence signature is a very powerful tool for distinguishing antineutrinos from backgrounds produced by other particles

To compensate for the loss in ν ¯ e }_} flux due to the long baseline, KamLAND has a much larger detection volume compared to earlier devices The KamLAND detector uses a 1,000-metric-ton detection mass, which is over twice the size of similar detectors, such as Borexino However, the increased volume of the detector also demands more shielding from cosmic rays, requiring the detector be placed underground

As part of the Kamland-Zen double beta decay search, a balloon of scintillator with 320 kg of dissolved xenon was suspended in the center of the detector in 2011[3] A cleaner rebuilt balloon is planned with additional xenon KamLAND-PICO is a planned project that will install the PICO-LON detector in KamLand to search for dark matter PICO-LON is a radiopure NaITl crystal that observes inelastic WIMP-nucleus scattering[4] Improvements to the detector are planned, adding light collecting mirrors and PMTs with higher quantum efficiency

Results

Neutrino oscillation

KamLAND started to collect data on January 17, 2002 First results were reported using only 145 days of data[5] Without neutrino oscillation, 7001868000000000000♠868±56 events were expected, however, only 54 events were observed KamLAND confirmed this result with a 515-day data sample,[6] 3652 events were predicted in the absence of oscillation, and 258 events were observed These results established antineutrino disappearance at high significance

The KamLAND detector not only counts the antineutrino rate, but also measures their energy The shape of this energy spectrum carries additional information that can be used to investigate neutrino oscillation hypotheses Statistical analyses in 2005 show the spectrum distortion is inconsistent with the no-oscillation hypothesis and two alternative disappearance mechanisms, namely the neutrino decay and de-coherence models[citation needed] It is consistent with 2-neutrino oscillation and a fit provides the values for the Δm2 and θ parameters Since KamLAND measures Δm2 most precisely and the solar experiments exceed KamLAND's ability to measure θ, the most precise oscillation parameters are obtained in combination with solar results Such a combined fit gives Δ m 2 = 79 − 05 + 06 ⋅ 10 − 5 eV 2 }=79_^\cdot 10^}^} and tan 2 ⁡ θ = 040 − 007 + 010 \theta =040_^} , the best neutrino oscillation parameter determination to that date Since then a 3 neutrino model has been used

Precision combined measurements were reported in 2008[7] and 2011:[8]

Δ m 21 2 = 759 ± 021 ⋅ 10 − 5 eV 2 , tan 2 ⁡ θ 12 = 047 − 005 + 006 ^=759\pm 021\cdot 10^\,}^,\,\,\tan ^\theta _=047_^}

Geological antineutrinos geoneutrinos

KamLAND also published an investigation of geologically-produced antineutrinos so-called geoneutrinos in 2005 These neutrinos are produced in the decay of thorium and uranium in the Earth's crust and mantle[9] A few geoneutrinos were detected and this limited data were used to limit the U/Th radiopower to under 60TW

Combination results with Borexino were published in 2011,[10] measuring the U/Th heat flux

New results in 2013, benefiting from the reduced backgrounds due to Japanese reactor shutdowns, were able to constrain U/Th radiogenic heat production to 112 − 51 + 79 ^} TW [11] using 116 ν ¯ e }_} events This constrains composition models of the bulk silicate Earth and agrees with the reference Earth model

KamLAND-Zen Double Beta Decay Search

KamLAND-Zen uses the detector to study beta decay of 136Xe from a balloon placed in the scintillator in summer 2011 Observations set a limit for neutrinoless double-beta decay half-life of 7032599594400000000♠19×1025 yr[12] A double beta decay lifetime was also measured: 238 ± 002 s t a t ± 014 s y s t ∗ 10 21 }\pm }10^}  yr, consistent with other xenon studies[3] KamLAND-Zen plans continued observations with more enriched Xe and improved detector components

An improved search was published in August 2016, increasing the half-life limit to 7033337666320000000♠107×1026 yr, with a neutrino mass bound of 61–165 meV[13]

References

  1. ^ Iwamoto, Toshiyuki February 2003, Measurement of Reactor Anti-Neutrino Disappearance in KamLAND PDF PhD thesis, Tohoku University, archived from the original PDF on 2014-10-06 
  2. ^ Suzuki, Atsuto; Collaboration, KamLand 2005-01-01 "Results from KamLAND Reactor Neutrino Detection" Physica Scripta 2005 T121: 33 Bibcode:2005PhST12133S doi:101088/0031-8949/2005/T121/004 ISSN 1402-4896 
  3. ^ a b Gando, A; et al KamLAND-Zen Collaboration 19 April 2012 "Measurement of the double-β decay half-life of 136Xe with the KamLAND-Zen experiment" Physical Review C 85 4: 045504 arXiv:12014664  Bibcode:2012PhRvC85d5504G doi:101103/PhysRevC85045504 
  4. ^ Fushimi, K; et al 2013 "PICO-LON Dark Matter Search" Journal of Physics: Conference Series 469: 012011 Bibcode:2013JPhCS469a2011F doi:101088/1742-6596/469/1/012011  
  5. ^ Eguchi, K; et al KamLAND Collaboration 2003 "First results from KamLAND: evidence for reactor antineutrino disappearance" Physical Review Letters 90 2: 021802–021807 arXiv:hep-ex/0212021  Bibcode:2003PhRvL90b1802E doi:101103/PhysRevLett90021802 PMID 12570536 
  6. ^ Araki, T; et al KamLAND Collaboration 2005 "Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion" Physical Review Letters 94 8: 081801–081806 arXiv:hep-ex/0406035  Bibcode:2005PhRvL94h1801A doi:101103/PhysRevLett94081801 PMID 15783875 
  7. ^ Abe, S; et al KamLAND Collaboration 5 Jun 2008 "Precision Measurement of Neutrino Oscillation Parameters with KamLAND" Physical Review Letters 100 22: 221803 arXiv:08014589  Bibcode:2008PhRvL100v1803A doi:101103/PhysRevLett100221803 PMID 18643415 
  8. ^ Gando, A; et al 2011 "Constraints on θ13 from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND" Physical Review D 83 5: 052002 arXiv:10094771  Bibcode:2011PhRvD83e2002G doi:101103/PhysRevD83052002 
  9. ^ Araki, T; et al KamLAND Collaboration 2005 "Experimental investigation of geologically produced antineutrinos with KamLAND" Nature 436 7050: 499–503 Bibcode:2005Natur436499A doi:101038/nature03980 PMID 16049478 
  10. ^ Gando, A; et al KamLAND Collaboration 17 July 2011 "Partial radiogenic heat model for Earth revealed by geoneutrino measurements" Nature Geoscience 4 9: 647–651 Bibcode:2011NatGe4647K doi:101038/ngeo1205 
  11. ^ A Gando et al KamLAND Collaboration 2 August 2013 "Reactor on-off antineutrino measurement with KamLAND" Physical Review D 88 3: 033001 arXiv:13034667  Bibcode:2013PhRvD88c3001G doi:101103/PhysRevD88033001 
  12. ^ Gando, A; et al KamLAND-Zen Collaboration 7 February 2013 "Limit on Neutrinoless ββ Decay of 136Xe from the First Phase of KamLAND-Zen and Comparison with the Positive Claim in 76Ge" Physical Review Letters 110 6: 062502 arXiv:12113863  Bibcode:2013PhRvL110f2502G doi:101103/PhysRevLett110062502 PMID 23432237 
  13. ^ Gando, A; et al KamLAND-Zen Collaboration 16 August 2016 "Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen" Physical Review Letters 117 8: 082503 arXiv:160502889  Bibcode:2016PhRvL117h2503G doi:101103/PhysRevLett117082503 PMID 27588852 

Further reading

  • Abe, S; et al KamLAND Collaboration 2008 "Precision Measurement of Neutrino Oscillation Parameters with KamLAND" Physical Review Letters 100 22: 221803 arXiv:08014589  Bibcode:2008PhRvL100v1803A doi:101103/PhysRevLett100221803 PMID 18643415 
  • Eguchi, K; et al KamLAND Collaboration 2004 "High sensitivity search for
    ν
    e's from the sun and other sources at KamLAND" Physical Review Letters 92 7: 071301–071305 arXiv:hep-ex/0310047  Bibcode:2004PhRvL92g1301E doi:101103/PhysRevLett92071301 

External links

  • KamLAND official website
  • KamLAND at Lawrence Berkeley National Laboratory Berkeley Lab

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    29.10.2014


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