T2K experiment

T2K (Tokai to Kamioka, Japan) is a particle physics experiment that is a collaboration between several countries, including Japan, Canada, France, Germany, Italy, South Korea, Poland, Russia, Spain, Switzerland, the United States, and the United Kingdom. It is the second generation follow up to the K2K experiment, a similar long baseline neutrino oscillation experiment. T2K (Tokai to Kamioka, Japan) is a particle physics experiment that is a collaboration between several countries, including Japan, Canada, France, Germany, Italy, South Korea, Poland, Russia, Spain, Switzerland, the United States, and the United Kingdom. It is the second generation follow up to the K2K experiment, a similar long baseline neutrino oscillation experiment. The J-PARC facility produces an intense off-axis beam of muon neutrinos. The beam is directed towards the Super-Kamiokande detector, which is 295 km away. The main goal of T2K is to measure the oscillation of νμ to νe and to measure the value of θ13, one of the parameters of the Pontecorvo–Maki–Nakagawa–Sakata matrix. On June 15, 2011, the T2K collaboration announced the observation of six electron neutrino-like events compared to an expected background of 1.5, a significance of 2.5 standard deviations. On July 19, 2013, at the European Physical Society meeting in Stockholm, the international T2K collaboration announced a definitive observation of muon neutrino to electron neutrino transformation. On August 4, 2017, Mark Hartz revealed at a KEK seminar that the latest data from T2K hinted at CP violation, rejecting the hypothesis that neutrinos and antineutrinos oscillate with the same probability at the 95% confidence (2σ) level. The goal of the T2K experiment is to gain a more complete understanding of neutrino oscillation parameters. Previous neutrino experiments observed the disappearance of muon neutrinos in a beam as they oscillate to tau neutrinos, but oscillation from νμ to νe was not observed until July 19, 2013. The reason for this is that the mixing angle θ13, that controls the probability for this oscillation, is very small. T2K was the first experiment to measure the appearance of electron neutrinos in a muon neutrino beam. T2K's ND280 detector will take data on neutrino interaction cross section measurements on water. Precise measurements of the other neutrino mixing parameter Δm223 and θ23 are another aim of the experiment. Future upgrades to T2K could yield measurement of the CP violation phase δ by comparing oscillations of neutrinos to those of antineutrinos. The J-PARC facility has a more powerful accelerator than the KEK facility used in the K2K experiment. The main synchrotron will eventually be able to accelerate protons to 50 GeV/c. Protons colliding with the target material will produce (mostly) positive pions which will decay into antimuons and muon neutrinos. The beam power is expected to be 0.75 MW delivering 110 times more neutrino events than K2K. The neutrino beam at J-PARC is designed so that it is directed 2 to 3 degrees away from the Super-Kamiokande detector. This lowers the flux of neutrinos reaching the detector but provides a more desirable neutrino energy spectrum. Off-axis the peak energy is low with higher energies being suppressed. At the distance between Tokai and Kamioka, maximal neutrino oscillation is expected to occur at energies lower than 1 GeV. The near detector 280 meters (ND280) from the graphite target is a segmented detector composed of neutrino targets inside a tracking system surrounded by a magnet taken from the UA1 experiment. ND280 is able to measure the neutrino beam's energy spectrum, flux, flavor content, and interaction cross-sections before the neutrino oscillation. The detector is located 280 m from the target in the off-axis direction.