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First result of the muon antineutrino disappearance by T2K

On May 15th, 2015, Dr. Asher C. Kaboth, from Imperial College London, presented “The first result of the muon antineutrino disappearance by T2K” at a KEK IPNS Physics Seminar, which was held at Tokai Campus.

He showed the first T2K muon-antineutrino disappearance measurment results and a comparison between the new result and past results obtained using a neutrino beam.

The T2K experiment observed electron-neutrino appearance from a muon-neutrino beam in 2012. This observation will enable T2K to begin to explore CP violation in the lepton sector by comparing electron-neutrino appearance and electron-antineutrino appearance.

Only a small portion of the produced muon neutrino oscillates to electron neutrinos; and the majority oscillates to tau neutrinos. Because the energy of these tau neutrinos is below the tau-production threshold in the T2K far detector, these muon neutrinos effectively ‘disappear’. This oscillation process is therefore called “muon-neutrino disappearance mode”.

Using the disappearance mode, we can measure neutrino oscillation parameters which represent the neutrino misxing probabilit y (sin223)) and mass squared difference (Δm232).

Since 2014, T2K has been accumulating data with a muon antineutrino beam. If the antineutrino beam measurement results are different than the the neutrino beam measurement results, this could be a major discovery, showing a never-before-seen difference between matter and antimatter in leptons.

Dr. Kaboth showed that the muon-antineutrino oscillation parameters are Δ m322 = 2.33 +0.27-0.23 × 10-3 eV2 and sin223) = 0.515 +0.085-0.095.

This result is consistent with the T2K muon-neutrino disapearance result published in 2013, and also consistent with the MINOS muon-antineutrino disapearance results.

Currently there is no evidence of matter and antimatter difference in leptons. T2K experimental group keeps on taking more muon-antineutrino data for precision measurement. Let’s look forward to further masurement results from the T2K !

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