Exploring a high-density regime in the QCD Phase diagram at J-PARC Heavy-Ion Project (J-PARC-HI)

J-PARC (Japan Proton Accelerator Research Complex) is one of the world’s highest-intensity proton accelerators for material and life sciences, neutrino physics, and hadron and nuclear physics in the GeV energy range. We are planning a future project, J-PARC-HI, to accelerate world's highest-intensity heavy-ion beams at J-PARC. For the acceleration scheme, a new heavy-ion linac and a booster ring are required as an injector, while the heavy-ion beams can be accelerated in the existing 3-GeV synchrotoron (RCS) and 30-GeV synchrotoron (MR) . The maximum beam rate is expected to reach 10¹¹ Hz, which is the world's highest intensity for the heavy-ion beam, and the energy can vary from 1 to 12 AGeV/c. We will explore QCD phase structures in a high-baryon density regime such as the first-order phase boundary, the QCD critical point, and QCD superconducting phases with various probes such as event-by-event fluctuations, dileptons, collective flow, and two-particle correlations. We also search for various multi-strangeness particles/nuclei and study hadron-hadron interactions including strangeness. In this talk, we introduce the overview of J-PARC-HI including the staging strategy with a low-intensity injector and an experiment at the existing J-PARC E16 spectrometer (Phase 1), and with a high-intensity injector and an experiment with a new large acceptance spectrometer (Phase 2). We show the status of the dilepton measurements in a p+A collisions at J-PARC E16 which serves as a baseline experiment for J-PARC-HI. Then, we will show some of the physics feasibility for dilepton and hadron measurements at J-PARC-HI.