J-PARC

Nuclear and Particle Physics at J-PARC

Experimental studies of nuclei and elementary particles are conducted at the Nuclear and Particle Physics Facility at the Japan Proton Accelerator Research Complex (J-PARC). Secondary beams of hadrons (such as kaons) and neutrinos are generated from the high-intensity proton beam produced in the 50 GeV synchrotron (Main Ring).

Hadron Experiments

Hadrons are particles composed of two or more quarks bound together by the strong force. Hadrons interact through fundamental forces such as the strong force and the weak force.

The experimenters at the Hadron Hall study the characteristics of the strong force and the structure of hadrons and nuclei. Their goal is to achieve an understanding of quantum many-body systems through, in particular, the behavior of unusual hadrons. Such hadrons include the hypernucleus, which contains ‘strange’ quarks; and exotic hadrons, which cannot be understood in terms of the usual three-quark hadrons or quark-antiquark bound states.

The experimenters also study the weak force via rare decay modes of K mesons. In these decays, they look for any differences in the degree of violation of charge-parity symmetry (CP) and time reversal symmetry (T) between quarks and antiquarks. Such symmetry breaking provides them with clues to discover potential new physics beyond the Standard Model.

Neutrino Experiment

Neutrinos are small, electrically neutral particles that rarely interact with ordinary matter. There are three types of neutrinos: the electron neutrino, the muon neutrino, and the tau neutrino. Sometimes these different types are also known as 'generations' or 'flavors.'

Neutrino properties, even properties as basic as their mass, are still not well measured. The Tokai-to-Kamioka (T2K) neutrino oscillation experiment aims to measure the neutrino masses and the degrees of flavor mixture. A beam of pure muon neutrinos (more than 99% pure) produced at the J-PARC accelerator in Tokai travels 295 kilometers to a neutrino observatory in Gifu, the Super-Kamiokande. As the neutrinos travel underground, they change flavors at a rate that is related to their mass and mixing. This phenomenon is called neutrino oscillation. Using the high-intensity neutrino beam produced at the J-PARC, the T2K neutrino experiment will explore this neutrino oscillation with unprecedented precision. It may possibly investigate the mystery of the matter-antimatter asymmetry in neutrinos to advance our knowledge of the origin of matter.