Please also visit our official K2K home page at KEK.
K2K, which stands for "KEK to Kamioka", is a so-called "Long baseline neutrino oscillation" experiment and shouldn't be confused with the Y2K problem! KEK is a Japanese national laboratory for High Energy Accelerator Research and it is located in Tsukuba city, near Tokyo on the east coast of the main island of Japan. Kamioka is a tiny mining town on the west coast, 250 km away from KEK, and it is the site of a mine which houses the now-famous Super-Kamiokande detector. The experiment is called a long baseline experiment because we send a neutrino beam generated at the KEK neutrino beam line all the way to Kamioka, mostly through the earth, to observe the "neutrino oscillation" phenomenon. See the figure below.
The neutrino is a mysterious elementary particle that has no electric charge and interacts little with any other matter. It can travel through 50 billion miles of water without interacting. On the surface of the earth, about a half of a trillion neutrinos from the sun pass through each square centimeter of area every second. It is also believed that there are 300 relic neutrinos per cubic centimeter of a volume in our universe which were produced about one second after the Big-bang. Thus, if the neutrino has non-zero mass, it can contribute to the mass and ultimate fate of the universe, i.e. the question of whether the universe is open (forever expanding) or closed (eventually contracting to a "Big Crunch").
In the "Standard Model" of elementary particle physics, there are three kinds of neutrinos, electron-neutrino, muon-neutrino and tau-neutrino, and in this extremely successful model, all the neutrinos are assumed to have zero mass. However, in most of the Grand Unified Theories, which attempt to generalize the Standard Model, neutrinos posses very tiny but non-zero mass. If and only if neutrinos have non-zero masses, it can be shown that the neutrinos can "oscillate" from one type to another. For example, a muon-neutrino can transform into a tau-neutrino which in turn can transform back to a muon neutrino and so on. This quantum mechanical phenomenon is called "Neutrino Oscillation" and any convincing observation of neutrino oscillation provides a direct proof of non-zero neutrino mass.
The major goal of the K2K experiment is to observe the neutrino oscillation phenomenon. In particular, we are trying to confirm the results of the Super-Kamiokande experiment, which observed neutrino oscillations by studying the neutrinos from Earth's atmosphere. (See the announcement made in June 1998.) To achieve this goal, we utilize the KEK neutrino beam generated by using the KEK proton synchrotron. High energy protons (12 GeV beam energy) accelerated by the synchrotron hit an aluminum target and produce many "hadron" particles, most of which are pions. These pions are then focused by a pair of magnetic instrument called "neutrino horns" and subsequently decay to muons and muon-neutrinos. The muon neutrinos are then sent through the nearby neutrino detector complex (Near Detector), 300 meters away from the target inside the KEK laboratory, and then to the Super-Kamiokande detector (Far Detector), 250 km away.
The K2K near detector complex consists of sophisticated particle detectors: a one kiloton water Cherenkov detector (a miniature Super-kamiokande detector), a scintillating fiber tracker with water targets, a scintillator veto counter, a lead glass calorimeter and a muon ranger. Neutrino Oscillation phenomenon can be examined by comparing the observed neutrinos at the near detector and the far detector.
The K2K near detector construction was completed in January 1999 and the neutrino beam line commissioning was started on January 27, 1999. On March 5, 1999, we started K2K physics data taking run and we are currently (June 1999) taking data. Among all planned or proposed long baseline experiments, K2K is the first one to be online.
The K2K collaboration is an international consortium of institutions from Japan, Korea, and the United States. There are about 100 collaborating members from 20 institutions.
The Stony Brook Super-Kamiokande/K2K group is composed of Professor C. K. Jung who is a Co-spokesperson of the US K2K collaboration, a senior research scientist Dr. C. Yanagisawa, three research associates Drs. J. Hill, K. Martens and C. McGrew, four graduate students M. Malek, C. Mauger, E. Sharkey and B. Viren, and two undergraduate students T. Kato and T. Raza. In the past, a total of three graduate students and twelve undergraduate students have done research work with the group, many of whom have traveled to Japan to participate in the detector construction and related research activities. The Stony Brook group has been participating in the Super-Kamiokande experiment since 1992, and in the K2K experiment since 1996.