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Neutrino mass is one of the great mysteries of the current understanding of elementary particle physics. To verify or deny the possibility of neutrino mass, we are starting a long baseline neutrino oscillation experiment (K2K), using the 12GeV proton synchrotron accelerator at the High Energy Accelerator Research Organization (KEK) in Tsukuba city in Ibaraki Prefecture, and the Super-Kamiokande detector which lies 250km away in Kamioka town in Gifu Prefecture, operated by Institute of Cosmic Ray Research (ICRR), University of Tokyo. At the KEK site, we create a neutrino beam and do a very precise measurement of the beam flux and the contamination of wrong species of neutrino, using a set of nearby detectors. Then we can look for any possible effects due to neutrino oscillations by comparing the Super-Kamiokande measurement with the front detector measurement.

The long baseline neutrino oscillation experiment, K2K:

The above piece of a map of Japan has some important points about the K2K experiment in it. Basically, the thick black arrow is the 250 Km path which the neutrinos will follow from KEK to Super-Kamiokande. The scenic northern "Japan Alps" under which our beam will travel. The central expanded section on the right is a caricature of the KEK laboratory grounds, with further details shown depicting our beam target area and front detector hall.
At KEK, the intense proton beam from 12GeV proton synchrotron produces numerous pi-mesons at the production target made of aluminum. These pi-mesons are focused to decay into muons and neutrinos in the 200-m decay pipe. The neutrinos emerged from the dump shield pass through the front detector and travel to Super-Kamiokande within a millisecond.

We have a 1 kiloton water Cherenkov detector (maintained by ICRR) and a fine grain scintillating fiber detector to measure the neutrino flux and beam composition at the KEK site. Behind the fine grain detector, there is an array of lead glass to measure the beam composition, and then a "Muon " which is a stack of iron plates and wire chamber detectors to measure the muon spectrum accurately. This whole suite of detectors sits in a hole below ground level so that the beam center can be properly aimed at the far detector. Because of the earth's curvature the straight line from the target to Super-Kamiokande points down by about one and a half degrees into the ground.

Front detector hall of K2K:

Links:

• K2K home page
  
• Super Kamokande home page
  
• KEK home page