View source for Kamioka Liquid Scintillator Antineutrino Detector

{{Short description|Neutrino oscillation experiment in Japan}}
[[Image:KamLAND schematic.png|right|thumb|300px|Schematic of the KamLAND detector]]
{{coord|36.4225|N|137.3153|E|region:JP-21_type:landmark|display=title|notes=<ref name=IwamotoToshiyuki>{{Citation |url=http://kamland.lbl.gov/Dissertations/IwamotoToshiyuki-DoctorThesis.pdf |first=Toshiyuki |last=Iwamoto |title=Measurement of Reactor Anti-Neutrino Disappearance in KamLAND |type=Ph.D. thesis |publisher=Tohoku University |date=February 2003 |url-status=dead |archive-url=https://web.archive.org/web/20141006103219/http://kamland.lbl.gov/Dissertations/IwamotoToshiyuki-DoctorThesis.pdf |archive-date=2014-10-06 }}</ref>{{Rp|105}}}}
The '''Kamioka Liquid Scintillator Antineutrino Detector (KamLAND)''' is an electron [[Neutrino|antineutrino]] detector at the [[Kamioka Observatory]], an underground [[Neutrino detector|neutrino detection facility]] in [[Hida, Gifu]], [[Japan]]. The device is situated in a [[Drift mining|drift mine]] shaft in the old [[Kamioka Observatory#KamiokaNDE|KamiokaNDE]] cavity in the [[Japanese Alps]]. Although located in the Kamioka Observatory, which is part of the [[University of Tokyo]], this project is conducted by a team at [[Tohoku University]]. The site is surrounded by 53 Japanese commercial [[nuclear reactor]]s. Nuclear reactors produce [[Electron neutrino#Electron antineutrino|electron antineutrino]]s (<math>\bar{\nu}_e</math>) during the decay of radioactive [[Nuclear fission product|fission product]]s in the [[nuclear fuel]]. Like the intensity of light from a light bulb or a distant star, the isotropically-emitted <math>\bar{\nu}_e</math> [[flux]] decreases at 1/R<sup>2</sup> per increasing distance R from the reactor. The device is sensitive up to an estimated 25% of [[neutrino#Reactor neutrinos|antineutrinos from nuclear reactors]] that exceed the [[threshold energy]] of 1.8 [[Electronvolt|megaelectronvolts]] (MeV) and thus produces a signal in the detector.

If neutrinos have mass, they may [[neutrino oscillation|oscillate]] into [[Flavour (particle physics)|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]].

==KamLAND Detector==
{{Unreferenced section|date=May 2014}}
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).<ref>{{Cite journal|last1=Suzuki|first1=Atsuto|last2=Collaboration|first2=KamLand|date=2005-01-01|title=Results from KamLAND Reactor Neutrino Detection|url=http://stacks.iop.org/1402-4896/2005/i=T121/a=004|journal=Physica Scripta|language=en|volume=2005|issue=T121|pages=33|doi=10.1088/0031-8949/2005/T121/004|issn=1402-4896|bibcode=2005PhST..121...33S|s2cid=250737408 }}</ref>  Photocathode coverage is 34%. Its second, inner layer consists of a {{val|13|u=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 3.2 kiloton cylindrical water [[Cherenkov detector]] surrounds the containment vessel, acting as a [[muon]] [[Neutrino detector#Background suppression|veto counter]] and providing shielding from [[cosmic ray]]s and [[Radioactive decay|radioactivity]] from the surrounding rock.

[[Electron neutrino#Electron antineutrino|Electron antineutrino]]s ({{Subatomic Particle|Electron antineutrino}}) are detected through the [[Inverse beta decay]] reaction <math>\bar{\nu}_e + p \to e^+ + n</math>, which has a 1.8 MeV <math>\bar{\nu}_e</math> [[threshold energy|energy threshold]]. The prompt scintillation light from the [[positron]] (<math>e^+</math>) gives an estimate of the incident antineutrino energy, <math>E_{\nu} = E_{prompt} + <E_n> + 0.9 MeV </math>, where <math>E_{prompt}</math> is the [[Prompt neutron|prompt]] event energy including the [[positron]] [[kinetic energy]] and the <math>e^+e^-</math>  [[annihilation]] energy. The quantity &lt;<math>E_n</math>&gt; is the average [[Neutron#Neutron detection by elastic scattering|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 {{val|2.2|u=MeV}} [[gamma ray|{{Subatomic Particle|Photon}} ray]]. This delayed-coincidence signature is a very powerful tool for distinguishing antineutrinos from [[Cosmic background (disambiguation)|backgrounds]] produced by other particles.

To compensate for the loss in <math>\bar{\nu}_e</math> 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&nbsp;kg of dissolved xenon was suspended in the center of the detector in 2011.<ref name=":0" /> 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 NaI(Tl) crystal that observes inelastic WIMP-nucleus scattering.<ref>{{Cite journal|title = PICO-LON Dark Matter Search |date = 2013|journal = [[Journal of Physics: Conference Series]]|volume = 469|issue = 1 |pages = 012011|doi = 10.1088/1742-6596/469/1/012011 |doi-access=free |bibcode = 2013JPhCS.469a2011F |last1 = Fushimi|first1 = K|display-authors=etal}}</ref>  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.<ref>{{ cite journal | last1=Eguchi |first1=K. |display-authors=etal |collaboration=KamLAND Collaboration | title=First results from KamLAND: evidence for reactor antineutrino disappearance |  journal=[[Physical Review Letters]] | volume=90 | issue=2 | pages=021802–021807 | doi=10.1103/PhysRevLett.90.021802 | date=2003 | pmid=12570536 | bibcode=2003PhRvL..90b1802E|arxiv = hep-ex/0212021|s2cid=119344739 }}</ref> Without [[neutrino oscillation]], {{val|86.8|5.6}} events were expected, however, only 54 events were observed. KamLAND confirmed this result with a 515-day data sample,<ref>{{ cite journal | last1=Araki |first1=T.  |display-authors=etal |collaboration=KamLAND Collaboration | title=Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion | journal=[[Physical Review Letters]] | volume=94 | issue=8 | date=2005 | pages=081801–081806 | doi=10.1103/PhysRevLett.94.081801 | pmid=15783875 | bibcode=2005PhRvL..94h1801A|arxiv = hep-ex/0406035|s2cid=119098950 }}</ref> 365.2 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.<ref>{{Cite journal |last1=Antonelli |first1=V. |last2=Miramonti |first2=L. |last3=Peña Garay |first3=C. |last4=Serenelli |first4=A. |date=2013 |title=Solar Neutrinos |journal=Advances in High Energy Physics |language=en |volume=2013 |pages=1–34 |doi=10.1155/2013/351926 |doi-access=free |issn=1687-7357|hdl=2434/219153 |hdl-access=free }}</ref>{{Citation needed|date=May 2014}} It is consistent with 2-neutrino oscillation and a fit provides the values for the Δm<sup>2</sup> and θ parameters. Since KamLAND measures Δm<sup>2</sup> 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 <math>\Delta{m^2} = 7.9^{+0.6}_{-0.5} \cdot 10^{-5} \text{eV}^2</math>  and <math>\tan^2\theta = 0.40^{+0.10}_{-0.07}</math> , 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<ref>{{Cite journal|title = Precision Measurement of Neutrino Oscillation Parameters with KamLAND|last= Abe |first=S.  |display-authors=etal |collaboration=KamLAND Collaboration |date = 5 Jun 2008|journal = [[Physical Review Letters]]|volume = 100|issue = 22|page = 221803|doi = 10.1103/PhysRevLett.100.221803 |pmid = 18643415|bibcode = 2008PhRvL.100v1803A|arxiv= 0801.4589|s2cid= 119291217 }}</ref> and 2011:<ref>{{Cite journal|title = Constraints on θ<sub>13</sub> from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND|date = 2011|journal = [[Physical Review D]]|volume = 83|issue = 5|page = 052002|doi = 10.1103/PhysRevD.83.052002|arxiv = 1009.4771 |bibcode = 2011PhRvD..83e2002G |last1 = Gando|first1 = A.  | s2cid=118444976 |display-authors=etal}}</ref>

:<math>\Delta m_{21}^2 = 7.59 \pm 0.21 \cdot 10^{-5} \, \text{eV}^2,\,\, \tan^2 \theta _{12} = 0.47^{+0.06}_{-0.05}</math>

===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 (geology)|crust]] and [[Mantle (geology)|mantle]].<ref>{{cite journal |last1=Araki |first1=T.  |display-authors=etal |collaboration=KamLAND Collaboration | title=Experimental investigation of geologically produced antineutrinos with KamLAND | journal=[[Nature (journal)|Nature]] | volume=436 | issue=7050 | date=2005 | pages=499–503 | doi=10.1038/nature03980 | pmid=16049478 |bibcode = 2005Natur.436..499A|s2cid=4367737 }}</ref> A few geoneutrinos were detected and these limited data were used to limit the U/Th radiopower to under 60TW.

Combination results with Borexino were published in 2011,<ref>{{Cite journal|url = https://authors.library.caltech.edu/25422/1/Gando2011p15815Nat_Geosci.pdf|title = Partial radiogenic heat model for Earth revealed by geoneutrino measurements|last1= Gando|first1=  A.|display-authors=etal |collaboration=KamLAND Collaboration |date = 17 July 2011|journal = [[Nature Geoscience]]|volume = 4|issue = 9|pages = 647–651|doi = 10.1038/ngeo1205|bibcode = 2011NatGe...4..647K}}</ref> 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 <math>11.2^{+7.9}_{-5.1}</math> TW <ref>{{cite journal|last1=A. Gando et al. (KamLAND Collaboration)|title=Reactor on-off antineutrino measurement with KamLAND|journal=[[Physical Review D]] |volume = 88 |issue=3| page = 033001|date=2 August 2013|doi=10.1103/PhysRevD.88.033001|bibcode = 2013PhRvD..88c3001G |arxiv=1303.4667|s2cid=55754667}}</ref> using 116 <math>\bar{\nu}_e</math> 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 <sup>136</sup>Xe from a balloon placed in the scintillator in summer 2011. Observations set a limit for neutrinoless double-beta decay half-life of {{val|1.9|e=25|u=yr}}.<ref>{{Cite journal|title=Limit on Neutrinoless ββ Decay of <sup>136</sup>Xe from the First Phase of KamLAND-Zen and Comparison with the Positive Claim in <sup>76</sup>Ge |date=7 February 2013 |journal=[[Physical Review Letters]] |volume=110 |issue=6| page=062502 |doi=10.1103/PhysRevLett.110.062502 |bibcode=2013PhRvL.110f2502G |last1=Gando |first1=A. |collaboration=KamLAND-Zen Collaboration |arxiv=1211.3863 |pmid=23432237|s2cid=32541533 }}</ref>  A double beta decay lifetime was also measured: <math>2.38 \pm{0.02(\mathrm{stat})} \pm{0.14(\mathrm{syst})}  *10^{21}</math>&nbsp;yr, consistent with other xenon studies.<ref name=":0">{{Cite journal |title=Measurement of the double-β decay half-life of <sup>136</sup>Xe with the KamLAND-Zen experiment |last1=Gando |first1=A. |collaboration=KamLAND-Zen Collaboration |date=19 April 2012 |journal=[[Physical Review C]] |volume=85 |issue=4 |page=045504 |doi=10.1103/PhysRevC.85.045504 |bibcode=2012PhRvC..85d5504G |arxiv=1201.4664|s2cid=123986835 }}</ref>  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 {{val|1.07|e=26|u=yr}}, with a neutrino mass bound of 61–165&nbsp;meV.<ref>{{Cite journal |last1=Gando |first1=A. |collaboration=KamLAND-Zen Collaboration |date=16 August 2016 |title=Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen |journal=[[Physical Review Letters]] |volume=117 |issue=8 |pages=082503 |doi=10.1103/PhysRevLett.117.082503 |pmid=27588852 |bibcode=2016PhRvL.117h2503G |arxiv=1605.02889|s2cid=204937469 }}</ref>

The first KamLAND-Zen apparatus, '''KamLAND-Zen 400''', completed two research programs, Phase I (2011 Oct. - 2012 Jun.) and Phase II (2013 Dec. - 2015 Oct.). The combined data of Phase I and II implied the lower bound <math>1.07 \times 10^{26}</math> years for the neutrinoless double beta decay half-life. The KamLAND-Zen 400 operated from 2011 October to 2015 October and was then replaced by KamLAND-Zen 800.<ref>{{Cite journal|arxiv = 2112.04918|doi = 10.3847/1538-4357/ac4e7e|title = A Search for Correlated Low-energy Electron Antineutrinos in KamLAND with Gamma-Ray Bursts|year = 2022|last1 = Abe|first1 = S.|last2 = Asami|first2 = S.|last3 = Gando|first3 = A.|last4 = Gando|first4 = Y.|last5 = Gima|first5 = T.|last6 = Goto|first6 = A.|last7 = Hachiya|first7 = T.|last8 = Hata|first8 = K.|last9 = Hosokawa|first9 = K.|last10 = Ichimura|first10 = K.|last11 = Ieki|first11 = S.|last12 = Ikeda|first12 = H.|last13 = Inoue|first13 = K.|last14 = Ishidoshiro|first14 = K.|last15 = Kamei|first15 = Y.|last16 = Kawada|first16 = N.|last17 = Kishimoto|first17 = Y.|last18 = Kinoshita|first18 = T.|last19 = Koga|first19 = M.|last20 = Maemura|first20 = N.|last21 = Mitsui|first21 = T.|last22 = Miyake|first22 = H.|last23 = Nakamura|first23 = K.|last24 = Nakamura|first24 = K.|last25 = Nakamura|first25 = R.|last26 = Ozaki|first26 = H.|last27 = Sakai|first27 = T.|last28 = Sambonsugi|first28 = H.|last29 = Shimizu|first29 = I.|last30 = Shirai|first30 = J.|journal = The Astrophysical Journal|volume = 927| issue=1 |page = 69| bibcode=2022ApJ...927...69A |s2cid = 245006046|display-authors = 1 | doi-access=free }}</ref>

The second KamLAND-Zen experiment apparatus, '''KamLAND-Zen 800''', with bigger balloon of about 750&nbsp;kg of Xenon was installed in the KamLAND detector 10 May 2018. The operation was expected to start winter 2018-2019 with 5 years of expected operation.<ref>{{Cite web |last=Yoshihito |first=Gando |date=14 September 2018 |title=Neutrinoless double beta decay search with KamLAND-Zen |url=https://web2.ba.infn.it/now/now2018/assets/yoshihitogandonow2018.pdf |access-date=4 November 2023 |website=web2.ba.infn.it}}</ref>

The KamLAND-Zen 800 experiment started data taking in January 2019 and first results were published in 2020.<ref>{{Cite journal|doi=10.1088/1742-6596/1468/1/012142|title=First results of KamLAND-Zen 800|year=2020|last1=Gando|first1=Yoshihito|journal=Journal of Physics: Conference Series|volume=1468|page=012142|s2cid=229257322 |doi-access=free}}</ref> In March 2022 the KamLAND-Zen Collaboration using the KamLAND-Zen 800 published results about neutrinoless double-beta decay in Xe-136 using data collected between February 5, 2019 and May 8, 2021. No neutrinoless double-beta decay was observed, and the established lower bound for half-life was T > <math>2.3 \times 10^{26}</math> yr corresponding to upper limits on the effective Majorana neutrino mass of 36 – 156 meV.<ref>{{Cite journal|arxiv = 2203.02139|last1 = Collaboration|first1 = KamLAND-Zen|title = Search for the Majorana Nature of Neutrinos in the Inverted Mass Ordering Region with KamLAND-Zen| journal=Physical Review Letters |year = 2023| volume=130 | issue=5 | page=051801 | doi=10.1103/PhysRevLett.130.051801 | pmid=36800472 | bibcode=2023PhRvL.130e1801A | s2cid=247244665 }}</ref>

The KamLAND-Zen collaboration is planning to construct another apparatus, '''KamLAND2-Zen''' in the long term.

==References==
{{reflist}}

==Further reading==
* {{ cite journal | last1=Abe |first1=S |display-authors=etal |collaboration=KamLAND Collaboration | title=Precision Measurement of Neutrino Oscillation Parameters with KamLAND | journal=[[Physical Review Letters]] | volume=100 | issue=22 | date=2008 | pages=221803 | doi=10.1103/PhysRevLett.100.221803 | pmid=18643415 | bibcode=2008PhRvL.100v1803A |arxiv=0801.4589|s2cid=119291217 }}
* {{ cite journal | last1=Eguchi |first1=K |display-authors=etal |collaboration=KamLAND Collaboration| title=High sensitivity search for {{Subatomic particle|electron antineutrino}}'s from the sun and other sources at KamLAND | journal=[[Physical Review Letters]] | volume=92 | issue=7 | pages=071301–071305 | doi=10.1103/PhysRevLett.92.071301 |pmid=14995837 | date=2004 | bibcode=2004PhRvL..92g1301E|arxiv = hep-ex/0310047|s2cid=119360978 }}

==External links==
* [http://www.awa.tohoku.ac.jp/kamland/ KamLAND official website]
* [http://kamland.lbl.gov/ KamLAND at Lawrence Berkeley National Laboratory (Berkeley Lab)]
*[https://inspirehep.net/experiments/1110499 KamLAND experiment] record on [[INSPIRE-HEP]]
{{Breakthrough Prize laureates}}
{{Neutrino detectors}}

[[Category:Particle experiments]]
[[Category:Neutrino observatories]]
[[Category:Reactor neutrino experiments]]