Proposal: JSNS$^2$-II

Understand

This article describes the goal and expected sensitivity of the JSNS$^2$-II experiment at J-PARC Materials and Life Science Experimental Facility (MLF).

• The JSNS$^2$-II experiment is the second phase of the JSNS$^2$ experiment (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) with two detectors which are located in 24 m (an existing detector) and 48 m (new one) baselines to improve the sensitivity of the search for sterile neutrinos, especially in the low $\Delta m^2$ region, which has been indicated by the global fit of the appearance mode.
• The new second detector has a similar structure as the existing JSNS$^2$ detector, which is already working.
• To compensate for the reduction of the neutrino flux due to the distance from the mercury target, the target mass of the Gd-loaded liquid scintillator which is the Linear AlkylBenzene (LAB) based liquid scintillator inside the acrylic vessel is 35 tons.