K2K experiment

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Japanese neutrino experiment

title: "K2K experiment" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["neutrino-experiments"] description: "Japanese neutrino experiment" topic_path: "general/neutrino-experiments" source: "https://en.wikipedia.org/wiki/K2K_experiment" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Japanese neutrino experiment ::

The K2K experiment (KEK to Kamioka) was a neutrino experiment that ran from June 1999 to November 2004. It used muon neutrinos from a well-controlled and well-understood beam to verify the oscillations previously observed by Super-Kamiokande using atmospheric neutrinos. This was the first positive measurement of neutrino oscillations in which both the source and detector were fully under experimenters' control.{{cite journal |date=18 August 2000 |title=Synthetic neutrinos appear to disappear |url=http://cerncourier.com/cws/article/cern/28279 |journal=CERN Courier |volume=40 |issue=7 |archive-date=14 December 2010 |access-date=3 September 2010 |archive-url=https://web.archive.org/web/20101214162023/http://cerncourier.com/cws/article/cern/28279 |url-status=dead |author=N. Nosengo |date=2006 |title=Neutrinos make a splash in Italy |journal=Nature |pmid=16971911 |volume=443 |issue=7108 |page=126 |doi=10.1038/443126a |bibcode = 2006Natur.443..126N |url=https://cds.cern.ch/record/988253 |doi-access=free

Experimental design

K2K is a neutrino experiment which directed a beam of muon neutrinos () from the proton synchrotron at the KEK, located in Tsukuba, Ibaraki, to the Kamioka Observatory, located in Kamioka, Gifu, about 250 km away. |date=13 June 2002 |title=Long Baseline neutrino oscillation experiment, from KEK to Kamioka (K2K) |url=http://neutrino.kek.jp/intro/k2k.html |publisher=High Energy Accelerator Research Organization |access-date=2010-09-03

The proton beam from the synchrotron was directed onto an aluminium target, and the resulting collisions produced a copious amount of pions. These pions were then focused into a 200 m decay pipe, where they would decay into muons and muon neutrinos. The muons were stopped at the end of the pipe, leaving a beam of muon neutrinos. The exact composition of the beam contained over 97% muon neutrinos, with the other 3% being made of electron neutrinos (), electron antineutrinos () and muon antineutrinos ().

After they exited the pipe, the neutrinos went through a 1-kiloton water Cherenkov neutrino detector ("near detector") located at about 300 m from the aluminium target to determine the neutrino beam characteristics. This 1-kiloton "near detector" was a scaled-down version of the 50-kiloton Super-Kamiokande "far detector" located at the Kamioka Observatory, which allowed scientists to eliminate certain systematic uncertainties that would be present if two different detector types were used.{{cite web |date=19 June 1999 |title=K2K: Near Detector |url=http://k2k.physics.sunysb.edu/k2k/near_detector.shtml |publisher=[Stony Brook Super-Kamiokande/K2K group] |access-date=2010-09-03 |archive-date=20 July 2011 |archive-url=https://web.archive.org/web/20110720053235/http://k2k.physics.sunysb.edu/k2k/near_detector.shtml |date=20 June 1999 |title=K2K: Introduction |url=http://k2k.physics.sunysb.edu/k2k/intro.shtml |publisher=[Stony Brook Super-Kamiokande/K2K group] |access-date=2010-09-03 |archive-date=20 July 2011 |archive-url=https://web.archive.org/web/20110720052309/http://k2k.physics.sunysb.edu/k2k/intro.shtml

Collaboration

The K2K collaboration consisted of roughly 130 physicists from 27 universities and research institutes from all over the world, listed below. |date=20 January 2004 |title=K2K Member Institutes |url=http://neutrino.kek.jp/member.html |publisher=High Energy Accelerator Research Organization |access-date=2010-09-03

Results

The final K2K results found that at 99.9985% confidence (4.3 σ) there had been a disappearance of muon neutrinos. Fitting the data under the oscillation hypothesis, the best fit for the square of the mass difference between muon neutrinos and tau neutrinos was Δm2 = . |author = M. H. Ahn |collaboration=K2K Collaboration |year = 2006 |title = Measurement of Neutrino Oscillation by the K2K Experiment |journal = Physical Review D |volume = 74|article-number = 072003 |doi = 10.1103/PhysRevD.74.072003 |arxiv=hep-ex/0606032 |bibcode = 2006PhRvD..74g2003A |issue = 7 |s2cid=22053653 |author=Y. Fukuda |collaboration=Super-K Collaboration |date=1998 |title=Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days |journal=Physical Review Letters |volume=81 |pages=1158–1162 |doi=10.1103/PhysRevLett.81.1158 |bibcode=1998PhRvL..81.1158F |arxiv = hep-ex/9805021 |issue=6 |s2cid=14217731 |author= |date=1998 |title=Erratum: Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days |journal=Physical Review Letters |volume=81 |page=4279 |doi=10.1103/PhysRevLett.81.4279 |bibcode=1998PhRvL..81.4279F |issue=19 |doi-access=free |author=D.G. Michael |collaboration=MINOS Collaboration |year=2006 |title=Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam |journal=Physical Review Letters |volume=97 |article-number=191801 |doi=10.1103/PhysRevLett.97.191801 |pmid=17155614 |arxiv=hep-ex/0607088 |bibcode=2006PhRvL..97s1801M |issue=19 |s2cid=119458915

References

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