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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 (sin²(θ₂₃)) 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 sin²(θ₂₃) = 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 !