Editing Super-Kamiokande (section)

==History==
[[File:Kamiokande89.JPG|thumb|right|A model of KamiokaNDE]]
Construction of the predecessor of the present [[Kamioka Observatory]], the [[Institute for Cosmic Ray Research]], [[University of Tokyo]] began in 1982 and was completed in April 1983. The purpose of the observatory was to determine the existence of [[proton decay]], one of the most fundamental questions of elementary particle physics.<ref>{{cite web |title=トップページ - Kamioka Observatory, ICRR, University of Tokyo |website=www-sk.icrr.u-tokyo.ac.jp |url=https://www-sk.icrr.u-tokyo.ac.jp/en/}}</ref><ref>{{cite web |title=Physics Home |website=phys.washington.edu |url=http://www.phys.washington.edu/~superk/ |access-date=20 November 2001 |url-status=dead |archive-url=https://web.archive.org/web/20040130175750/http://www.phys.washington.edu/~superk/ |archive-date=30 January 2004}}</ref><ref>{{cite web |title=Super-Kamiokande Photo Gallery |website=www-sk.icrr.u-tokyo.ac.jp |url=https://www-sk.icrr.u-tokyo.ac.jp/en/sk/experience/gallery/}}</ref><ref>{{cite web |title=Official report on the accident (in PDF format) |website=u-tokyo.ac.jp |url=http://www-sk.icrr.u-tokyo.ac.jp/cause-committee/1st/report-nov22e.pdf}}</ref><ref>{{cite web |title=Logbook entry of first neutrinos seen at Super-K generated at KEK |website=symmetrymagazine.org |url=http://www.symmetrymagazine.org/cms/?pid=1000327}}</ref>

The detector, named KamiokaNDE for Kamioka Nucleon Decay Experiment, was a tank {{Convert|16.0|m|ft|0|abbr=on}} in height and {{Convert|15.6|m|ft|1|abbr=on}} in width, containing 3,058 tonnes (3,400 US tons) of pure water and about 1,000 photomultiplier tubes (PMTs) attached to its inner surface. The detector was upgraded, starting in 1985, to allow it to observe solar neutrinos. As a result, the detector (KamiokaNDE-II) had become sensitive enough to detect ten [[supernova neutrinos|neutrinos]] from [[SN 1987A]], a [[supernova]] which was observed in the [[Large Magellanic Cloud]] in February 1987, and to observe solar neutrinos in 1988. The ability of the Kamiokande experiment to observe the direction of electrons produced in solar neutrino [[elastic scattering|interactions]] allowed experimenters to directly demonstrate for the first time that the Sun was a source of neutrinos.

While making discoveries in [[neutrino astronomy]] and neutrino astrophysics, Kamiokande never detected a proton decay, the primary goal for its construction. The absence of any such observation pushed back the possible half-life of any potential proton decay far enough to eliminate some of the [[Grand Unified Theory|GUT]] models which allow for such a decay. Other models predict a longer half-life, with rarer decays.

To increase the chance of detecting such decays, a larger detector was needed. A higher sensitivity was also necessary to obtain a higher statistical confidence in other detections. This led to the design and construction of Super-Kamiokande, with fifteen times the volume of water and ten times as many PMTs as Kamiokande.

The Super-Kamiokande project was approved by the Japanese Ministry of Education, Science, Sports and Culture in 1991 for total funding of approximately $100&nbsp;million. The American portion of the proposal, which was primarily to build the OD system, was approved by the United States Department of Energy in 1993 for $3 million. In addition, the United States has also contributed about 2000 20&nbsp;cm PMTs recycled from the [[Irvine–Michigan–Brookhaven (detector)|IMB experiment]].<ref name="auto1" />

Super-Kamiokande started operation in 1996 and announced the first evidence of [[neutrino oscillation]] in 1998.<ref>{{cite journal |author=Fukuda, Y. |display-authors=etal |journal=Physical Review Letters |volume=81 |issue=8 |pages=1562–1567 |title=Evidence for oscillation of atmospheric neutrinos |date=1998 |arxiv=hep-ex/9807003 |bibcode=1998PhRvL..81.1562F |doi=10.1103/PhysRevLett.81.1562 |s2cid=7102535}}</ref> This was the first experimental observation supporting the theory that the neutrino has non-zero [[mass]], a possibility that theorists had speculated about for years. The 2015 [[Nobel Prize in Physics]] was awarded to Super-Kamiokande researcher [[Takaaki Kajita]] alongside [[Arthur B. McDonald|Arthur McDonald]] at the [[Sudbury Neutrino Observatory]] for their work confirming neutrino oscillation.

On 12 November 2001, about 6,600 of the photomultiplier tubes [[implosion (mechanical process)|imploded]] in a [[chain reaction]], as the [[shock wave]] from the concussion of each imploding tube cracked its neighbours.<ref>{{cite web |date=15 November 2001 |title=Accident grounds neutrino lab |url=https://physicsworld.com/a/accident-grounds-neutrino-lab/ |website=physicsworld.com}}</ref> The detector was partially restored by redistributing the photomultiplier tubes which did not implode, and by adding protective [[acrylic glass|acrylic]] shells that are hoped will prevent another chain reaction from recurring (Super-Kamiokande-II).

In July 2005, preparations began to restore the detector to its original form by reinstalling about 6,000 PMTs. The work was completed in June 2006, whereupon the detector was renamed Super-Kamiokande-III. This phase of the experiment collected data from October 2006 till August 2008. At that time, significant upgrades were made to the electronics. After the upgrade, the new phase of the experiment has been referred to as Super-Kamiokande-IV. SK-IV collected data on various natural sources of neutrinos, as well as acted as the far detector for the Tokai-to-Kamioka (T2K) long baseline neutrino oscillation experiment.

SK-IV continued until June 2018. After that, the detector underwent a full refurbishment during Autumn of 2018. On 29 January 2019 the detector resumed data acquisition.<ref>{{cite journal |title=Neutrino hunt resumes, ITER's new confidence and Elsevier's woes |journal=Nature |volume=566 |issue=7742 |pages=12–13 |year=2019 |bibcode=2019Natur.566...12. |pmid=30728526 |doi=10.1038/d41586-019-00440-2 |doi-access=free}}</ref>

In 2020, the detector was upgraded for the [[#SuperKGd|SuperKGd]] project by adding a [[gadolinium]] salt to the ultrapure water in order to enable the detection of antineutrinos from supernova explosions.<ref name="Abe 2022">{{cite journal |last1=Abe |first1=K. |last2=Bronner |first2=C. |last3=Hayato |display-authors=etal |title=First gadolinium loading to Super-Kamiokande |journal=Nuclear Instruments and Methods in Physics Research Section A |volume=1027 |year=2022 |issn=0168-9002 |page=166248 |arxiv=2109.00360 |bibcode=2022NIMPA102766248A |doi=10.1016/j.nima.2021.166248 |s2cid=237372721}}</ref>