At 19:09(JST) on April 23, the Tokai to Kamioka (T2K) long baseline neutrino oscillation experiment confirmed the first neutrino beam production by observing the muons produced by the proton beam in the neutrino facility at Japan Proton Accelerator Complex (J-PARC).
"I am extremely happy to announce the commencement of T2K," says KEK Professor Takashi Kobayashi, the acting spokesperson of the experiment. "The idea of T2K to search for muon neutrinus to electron neutrinos appearance originated from Totsuka-san and Nishikawa-san in 1999 and the history of the T2K collaboration dates back to 2001, when the first Letter of Intent was published. Today marks the start of our journey to a new realm of neutrino oscillation observations."
Neutrinos are elementary particles that belong to a category called leptons. Three types of neutrinos are known: electron neutrinos, muon neutrinos and tau neutrinos. In 1998, the late Professor Yoji Totsuka, along with the Super-Kamiokande collaboration, first discovered a phenomenon called neutrino oscillation. They measured the ratio of muon neutrinos to electron neutrinos produced in the upper atmosphere by high energy cosmic rays. The ratio of the two types of neutrino varied as a function of the length of the flight path from their generation, which matched with a theoretical calculation of neutrino oscillation with finite masses.
"The K2K experiment generated muon neutrinos with the 12 GeV Proton Synchrotron at KEK," says Professor Koichiro Nishikawa, former spokesperson of K2K and T2K. "With this beam, we confirmed neutrino oscillations in muon neutrino disappearance mode in 2006. At J-PARC, we will have a hundred times more powerful neutrino beam, which will enable us to discover another type of oscillation between muon type and electron type."
Physicists are hoping to measure a parameter called theta13. "If the value of theta13 is in a certain range, we will have a new key to prepare yet another generation of future neutrino experiments," says Professor Kobayashi. "The results which T2K will reveal will mark a pivotal moment for the next generation of neutrino experiments."
J-PARC is a world-class high intensity proton accelerator research complex, which is jointly built by KEK and Japan Atomic Energy Agency (JAEA). The main ring of J-PARC successfully accelerated proton beams to 30 GeV in December.
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|Figure 1 : T2K neutrino beamline generates neutrino beam to Super-KAMIOKANDE 300km away from J-PARC in Tokai.|
|Figure 2 : T2K Neutrino Experimental Facility at J-PARC.|
|Figure 3 : Muon Monitor (upper photos) and the first signal from Muon Monitor (lower).|
|Figure 4 : T2K members celebrate the first beam in the control room.|