Science at J-PARC
 
A unique feature of J-PARC is that it is a multi-purpose facility to promote research on wide range of field utilizing single proton accelerator complex. How can we do it at J-PARC ? Usually an accelerator facility, in a large scale and expensive, is constructed for one major purpose. For example, a high-energy accelerator is constructed for particle physics to look for new particles not yet discovered, an electron (or positron) storage ring for intense X-rays, and a heavy-ion accelerator for medical applications. At the J-PARC accelerator complex, high intensity proton beams will be available in three different beam energies from three proton accelerators at the same time: a proton beam at 600 MeV (Million electron Volt) through a superconducting proton linac, a proton beam at 3 GeV (Giga electron Volt) with the beam current of 333 μA from the 3-GeV proton synchrotron, and a proton beam at 50 GeV from the 50-GeV proton synchrotron. Three proton beams are used for three different research fields: the 600 MeV proton beam for R&D studies toward accelerator-driven nuclear transmutation, the 3 GeV proton beam for materials and life science, and the 50 GeV proton beam for nuclear and particle physics.

The reason why we use three different proton beams for three different purposes is that the proton beams are utilized to produce various secondary beams for different purposes. The proton beam at 600 MeV produces abundant spallation neutrons, the one at 3 GeV produces pulsed neutron and muon beams, and the one at 50 GeV produces various meson beams including kaons and neutrino beam.

Neutron is a particle with almost the same mass as a proton (hydrogen nucleus) and at very low energy behaves as a wave like X-ray. They can probe the structure of various materials in atomic scales. They are more sensitive to light atoms, hydrogen atoms in particular, in a molecule compared with X-rays, and also a good probe for magnetic structures. Various applications to protein analysis, structural analyses for soft matter (liquid crystals, etc.) and high-temperature superconducting materials will be conducted at J-PARC.

An ordinary nucleus is composed of two kinds of quarks, “up” and “down” quarks, only. Kaon, which has a “strange” quark inside, is useful to implant “strange” quarks into a nucleus. Such exotic nucleus is called a hypernucleus. Study of hypernuclear properties would give us new insights on new kinds of nuclear force binding these quarks into a hypernucleus. The high intensity kaon beam at J-PARC will enable us to produce new types of hypernuclei abundantly.

There are three kinds of neutrino: electron neutrino, muon neutrino, and tau neutrino. They had been believed to be massless in the Standard Model of particle physics until neutrino oscillation phenomena were discovered recently. With very tiny masses, three neutrinos could be mixed each other. The origin of the neutrino mass is one of the great mysteries in particle physics. The details of the mixing of neutrinos will be investigated in high precision and in high sensitivity with high intensity neutrino beams at J-PARC.

We hope research at J-PARC will further evolve and be synthesized with each other to form new research areas in a future.

The author of this article, Professor Tomofumi Nagae has been taking a leading role in the J-PARC Project Office.