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K2K experiment

k2k experiment, k2k project
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[1][2] Previous experiments relied on neutrinos from the Sun or from cosmic sources The experiment found oscillation parameters which were consistent with those measured by Super-Kamiokande


  • 1 Experimental design
  • 2 Collaboration
  • 3 Results
  • 4 See also
  • 5 References
  • 6 External links

Experimental design

K2K is a neutrino experiment which directed a beam of muon neutrinos
μ from the 6991192261178439999♠12 GeV proton synchrotron at the KEK, located in Tsukuba, Ibaraki, to the Kamioka Observatory, located in Kamioka, Gifu, about 250 km away[3] The muon neutrinos travelled through Earth, which allowed them to oscillate change into other flavours of neutrinos, namely into electron neutrinos
e and tau neutrinos
τ K2K however, focused only on
μ →
τ oscillations[4]

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[3] 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
e, electron antineutrinos
e 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[5] This dual-detector configuration allowed the comparison of the neutrino beam at the near detector with the neutrino beam at the far detector to determine if neutrinos had oscillated or not[6]


The K2K collaboration consisted of roughly 130 physicists from 27 universities and research institutes from all over the world, listed below[7] The full list of scientists and their countries of origin is available on the K2K website

  • Boston University
  • Chonnam National University
  • Commissariat à l'énergie atomique de Saclay DSM-DAPNIA
  • Dongshin University
  • High Energy Accelerator Research Organization
  • Hiroshima University
  • Institute for Cosmic Ray Research
  • Institute for Nuclear Research
  • Kobe University
  • Korea University
  • Kyoto University
  • Massachusetts Institute of Technology
  • Niigata University
  • Okayama University
  • Sapienza University of Rome
  • Seoul National University
  • State University of New York at Stony Brook
  • Tokyo University of Science
  • Tohoku University
  • Autonomous University of Barcelona/IFAE
  • University of California, Irvine
  • University of Geneva
  • University of Hawaii
  • University of Tokyo
  • University of Washington
  • University of Valencia
  • University of Warsaw


The final K2K results found that at 999985% confidence 43 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 = 6997280000000000000♠28×10−3 eV2[4] This result is in good agreement with the previous Super-Kamiokande result,[8] and the later MINOS result[9]

See also

  • T2K experiment – the successor of the K2K experiment


  1. ^ "Synthetic neutrinos appear to disappear" CERN Courier 40 7 18 August 2000 
  2. ^ N Nosengo 2006 "Neutrinos make a splash in Italy" Nature 443 7108: 126 Bibcode:2006Natur443126N doi:101038/443126a PMID 16971911 
  3. ^ a b "Long Baseline neutrino oscillation experiment, from KEK to Kamioka K2K" High Energy Accelerator Research Organization 13 June 2002 Retrieved 2010-09-03 
  4. ^ a b c M H Ahn; et al K2K Collaboration 2006 "Measurement of Neutrino Oscillation by the K2K Experiment" Physical Review D 74 7: 072003 arXiv:hep-ex/0606032  Bibcode:2006PhRvD74g2003A doi:101103/PhysRevD74072003 
  5. ^ "K2K: Near Detector" Stony Brook Super-Kamiokande/K2K group 19 June 1999 Retrieved 2010-09-03  External link in |publisher= help
  6. ^ "K2K: Introduction" Stony Brook Super-Kamiokande/K2K group 20 June 1999 Retrieved 2010-09-03  External link in |publisher= help
  7. ^ "K2K Member Institutes" High Energy Accelerator Research Organization 20 January 2004 Retrieved 2010-09-03 
  8. ^ Y Fukuda; et al Super-K Collaboration 1998 "Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days" Physical Review Letters 81 6: 1158 arXiv:hep-ex/9805021  Bibcode:1998PhRvL811158F doi:101103/PhysRevLett811158  and erratum "Erratum: Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days" Physical Review Letters 81 19: 4279 1998 Bibcode:1998PhRvL814279F doi:101103/PhysRevLett814279 
  9. ^ DG Michael; et al MINOS Collaboration 2006 "Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam" Physical Review Letters 97 19: 191801 arXiv:hep-ex/0607088  Bibcode:2006PhRvL97s1801M doi:101103/PhysRevLett97191801 PMID 17155614 

External links

  • K2K official website
  • K2K publications

k2k experiment, k2k project

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K2K experiment

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