Status of the J-PARC E16 experiment

A new experiment is being prepared to measure vector meson mass spectra in nucleus. The mass spectra of vector mesons have important information about chiral properties of strongly-interacted QCD medium. They were intensively studied in high energy heavy-ion collisions, also in nucleus. Nucleus can be considered as a QCD medium which has a finite density. The experiment aims to provide basic experimental information for finite density medium.

The J-PARC E16 experiment will measure mass spectra of low mass vector mesons, such as rho, omega, and, phi, in nucleus. An electron-positron decay mode needs to be used to avoid a final state interaction. Note that the branching ratio of the electron-positron mode is very small (~10^-4) and a very thin target (0.1% radiation length) must be used to avoid a radiation tail in the mass spectra. Thus, a large acceptance spectrometer and a high intensity beam are required to have enough statistics. We developed a new beam line and a large acceptance spectrometer for the current experiment. The spectrometer also has a good capability of high counting rate (~5 kHz/mm^2 at maximum).

The first experiment is scheduled in January 2020. In this talk, results of detector R&D and status of constructions will be presented.