K2K experiment

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. |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 |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 |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. |access-date=2010-09-03

• 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 = . |doi-access=free

References