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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.

Experimental design

K2K is a neutrino experiment which directed a beam of muon neutrinos (νμ) from the 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 (νe) and tau neutrinos (ντ). K2K however, focused only on νμ →ντ 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 (νe), electron antineutrinos (νe) and muon antineutrinos (νμ).[4]

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]
Collaboration

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
CEA 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 Valencia
University of Warsaw
University of Washington

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 = 2.8×10−3 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

References

"Synthetic neutrinos appear to disappear". CERN Courier. 40 (7). 18 August 2000.
N. Nosengo (2006). "Neutrinos make a splash in Italy". Nature. 443 (7108): 126. Bibcode:2006Natur.443..126N. doi:10.1038/443126a. PMID 16971911.
"Long Baseline neutrino oscillation experiment, from KEK to Kamioka (K2K)". High Energy Accelerator Research Organization. 13 June 2002. Retrieved 3 September 2010.
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:2006PhRvD..74g2003A. doi:10.1103/PhysRevD.74.072003.
"K2K: Near Detector". [Stony Brook Super-Kamiokande/K2K group]. 19 June 1999. Retrieved 3 September 2010.
"K2K: Introduction". [Stony Brook Super-Kamiokande/K2K group]. 20 June 1999. Retrieved 3 September 2010.
"K2K Member Institutes". High Energy Accelerator Research Organization. 20 January 2004. Retrieved 3 September 2010.
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): 1158–1162.arXiv:hep-ex/9805021. Bibcode:1998PhRvL..81.1158F. doi:10.1103/PhysRevLett.81.1158. and erratum "Erratum: Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days". Physical Review Letters. 81 (19): 4279. 1998. Bibcode:1998PhRvL..81.4279F. doi:10.1103/PhysRevLett.81.4279.

D.G. 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:2006PhRvL..97s1801M. doi:10.1103/PhysRevLett.97.191801. PMID 17155614.

External links

K2K official website
K2K publications

vte

Breakthrough Prize laureates
Mathematics

Simon Donaldson, Maxim Kontsevich, Jacob Lurie, Terence Tao and Richard Taylor (2015) Ian Agol (2016) Jean Bourgain (2017) Christopher Hacon, James McKernan (2018) Vincent Lafforgue (2019) Alex Eskin (2020) Martin Hairer (2021)

Fundamental physics

Nima Arkani-Hamed, Alan Guth, Alexei Kitaev, Maxim Kontsevich, Andrei Linde, Juan Maldacena, Nathan Seiberg, Ashoke Sen, Edward Witten (2012) Special: Stephen Hawking, Peter Jenni, Fabiola Gianotti (ATLAS), Michel Della Negra, Tejinder Virdee, Guido Tonelli, Joseph Incandela (CMS) and Lyn Evans (LHC) (2013) Alexander Polyakov (2013) Michael Green and John Henry Schwarz (2014) Saul Perlmutter and members of the Supernova Cosmology Project; Brian Schmidt, Adam Riess and members of the High-Z Supernova Team (2015) Special: Ronald Drever, Kip Thorne, Rainer Weiss and contributors to LIGO project (2016) Yifang Wang, Kam-Biu Luk and the Daya Bay team, Atsuto Suzuki and the KamLAND team, Kōichirō Nishikawa and the K2K / T2K team, Arthur B. McDonald and the Sudbury Neutrino Observatory team, Takaaki Kajita and Yōichirō Suzuki and the Super-Kamiokande team (2016) Joseph Polchinski, Andrew Strominger, Cumrun Vafa (2017) Charles L. Bennett, Gary Hinshaw, Norman Jarosik, Lyman Page Jr., David Spergel (2018) Special: Jocelyn Bell Burnell (2018) Charles Kane and Eugene Mele (2019) Special: Sergio Ferrara, Daniel Z. Freedman, Peter van Nieuwenhuizen (2019) The Event Horizon Telescope Collaboration (2020) Eric Adelberger, Jens H. Gundlach and Blayne Heckel (2021) Special: Steven Weinberg (2021)

Life sciences

Cornelia Bargmann, David Botstein, Lewis C. Cantley, Hans Clevers, Titia de Lange, Napoleone Ferrara, Eric Lander, Charles Sawyers, Robert Weinberg, Shinya Yamanaka and Bert Vogelstein (2013) James P. Allison, Mahlon DeLong, Michael N. Hall, Robert S. Langer, Richard P. Lifton and Alexander Varshavsky (2014) Alim Louis Benabid, Charles David Allis, Victor Ambros, Gary Ruvkun, Jennifer Doudna and Emmanuelle Charpentier (2015) Edward Boyden, Karl Deisseroth, John Hardy, Helen Hobbs and Svante Pääbo (2016) Stephen J. Elledge, Harry F. Noller, Roeland Nusse, Yoshinori Ohsumi, Huda Zoghbi (2017) Joanne Chory, Peter Walter, Kazutoshi Mori, Kim Nasmyth, Don W. Cleveland (2018) C. Frank Bennett and Adrian R. Krainer, Angelika Amon, Xiaowei Zhuang, Zhijian Chen (2019) Jeffrey M. Friedman, Franz-Ulrich Hartl, Arthur L. Horwich, David Julius, Virginia Man-Yee Lee (2020) David Baker, Catherine Dulac, Dennis Lo, Richard J. Youle (2021)

vte

Neutrino detectors, experiments, and facilities
Discoveries

Cowan–Reines ( ν e) Lederman–Schwartz–Steinberger ( ν μ) DONUT ( ν τ) Neutrino oscillation SN 1987 neutrino burst

Operating
(divided by
primary
neutrino
source)
Astronomical

ANITA ANTARES ASD BDUNT Borexino BUST HALO IceCube LVD NEVOD SAGE Super-Kamiokande SNEWS

Reactor

Daya Bay Double Chooz KamLAND RENO STEREO

Accelerator

ANNIE ICARUS (Fermilab) MicroBooNE MINERνA MiniBooNE NA61/SHINE NOνA NuMI T2K

0νββ

AMoRE COBRA CUORE EXO GERDA KamLAND-Zen MAJORANA NEXT PandaX SNO+ XMASS

Other

KATRIN WITCH

Construction

ARA ARIANNA Baikal-GVD BEST DUNE Hyper-Kamiokande JUNO KM3NeT SuperNEMO FASERν

Retired

AMANDA CDHS Chooz CNGS Cuoricino DONUT ERPM GALLEX Gargamelle GNO Heidelberg-Moscow Homestake ICARUS IGEX IMB K2K Kamiokande KARMEN KGF LSND MACRO MINOS MINOS+ NARC NEMO OPERA RICE SciBooNE SNO Soudan 2 Utah

Proposed

CUPID GRAND INO LAGUNA LEGEND LENA Neutrino Factory nEXO Nucifer SBND UNO JEM-EUSO WATCHMAN

Cancelled

DUMAND Project Long Baseline Neutrino Experiment NEMO Project NESTOR Project SOX BOREX

See also

BNO (Baksan or Baxan Neutrino Observatory) Kamioka Observatory LNGS SNOLAB List of neutrino experiments

Physics Encyclopedia

World

Index

Hellenica World - Scientific Library

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