T2K experiment

T2K experiment. It is a long-baseline neutrino oscillation experiment located in Japan. The project studies the transformation of muon neutrinos into electron neutrinos as they travel 295 kilometers from a production site to a massive underground detector. This research probes fundamental parameters of the Standard Model and seeks evidence for charge-parity violation in the lepton sector.

Overview

The experiment's name stands for Tokai to Kamioka, referencing the journey from the J-PARC proton accelerator complex in Tokai, Ibaraki to the Super-Kamiokande detector in the Kamioka Observatory. This setup creates a powerful beam of muon neutrinos directed through the Earth's crust. Key institutions like the University of Tokyo, KEK, and international partners from CERN, United Kingdom, Canada, and France form the core collaboration. The design builds upon earlier discoveries made at the Kamiokande and Super-Kamiokande facilities, which were pivotal in confirming neutrino oscillation.

Scientific goals

A primary objective is the precise measurement of the mixing angle known as θ₁₃, a key parameter in the PMNS matrix which describes neutrino mixing. The collaboration aims to determine the magnitude of potential charge-parity violation by comparing oscillation probabilities for neutrinos and antineutrinos. This could help explain the matter-antimatter asymmetry observed in the universe. Furthermore, the experiment constrains other oscillation parameters like Δm²₃₂ and searches for sterile neutrinos beyond the three known flavors.

Experimental design

The neutrino beam originates at J-PARC, where protons from the Main Ring synchrotron strike a graphite target to produce pions and kaons. These particles are focused by magnetic horns into a decay volume, where they produce a nearly pure beam of muon neutrinos. A suite of near detectors, including INGRID and the ND280, located 280 meters from the target, characterizes the beam before oscillations occur. The far detector is the Super-Kamiokande, a 50,000-ton water Cherenkov detector housed in the Kamioka Mine.

Results and discoveries

In 2011, the collaboration announced the first direct observation of electron neutrino appearance from a muon neutrino beam, providing the initial evidence for a non-zero θ₁₃ angle. Subsequent data runs have significantly improved the precision on this parameter. The experiment has also reported tension between neutrino and antineutrino oscillation data, hinting at possible new physics. These findings have major implications for next-generation projects like the Hyper-Kamiokande and the Deep Underground Neutrino Experiment (DUNE) in the United States.

Collaboration and funding

The effort is managed by the T2K collaboration, comprising over 500 physicists from roughly 70 institutions in 14 countries. Major funding and support come from the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science, and agencies like the Science and Technology Facilities Council in the United Kingdom and the National Science Foundation in the United States. Partner laboratories include CERN, TRIUMF, and the Institut national de physique nucléaire et de physique des particules (IN2P3).

Category:Particle physics experiments Category:Neutrino experiments Category:J-PARC Category:Experiments in Japan