Speaker
Description
The JSNS²-II (J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source) experiment searches for sterile neutrino oscillations using neutrinos from muon decay at rest. At the J-PARC Material and Life Science Experimental Facility (MLF), a 3 GeV proton beam is injected onto a mercury target, producing muon antineutrinos. As the second phase of the JSNS², the experiment employs a two-detector configuration with a near detector (24 m) and a far detector (48 m), both based on gadolinium-loaded liquid scintillator targets, to reduce systematic uncertainties and improve sensitivity in the low Δm² region.
The far detector, located at an outdoor site, consists of a gadolinium-loaded liquid scintillator for the neutrino target surrounded by unloaded liquid scintillator for gamma catcher and veto regions. The detector employs 32 tons of Gd-loaded target and 10-inch 219 photomultiplier tubes (PMTs)—171 inner PMTs for neutrino event detection and 48 veto PMTs. Compared to the near detector (17 tons target, 120 PMTs), this represents approximately 2.2 times the target volume and 1.8 times the number of PMTs. The veto system serves as active shielding to reject cosmic rays and external background events, enabling their identification and removal during analysis. The detector has been completed and is currently in commissioning for the upcoming physics run.
To ensure stable detector operation, a Linux LabVIEW-based Slow Control and Monitoring System (SCM) continuously monitors detector environmental conditions, including temperature, pressure, and liquid levels. A Linux-based standalone High-Voltage Control and Monitoring System (HVCM) monitors PMT high-voltage stability. An embedded LED calibration system with 12 blue LEDs (420 nm), providing full detector coverage, and 2 UV LEDs (355 nm) at top and bottom positions, enables regular monitoring of PMT performance. Target gains are set to 5×10⁶ for inner PMTs and 3×10⁶ for veto PMTs to suppress PMT non-linearity and ensure the dynamic range.
This poster highlights the far detector configuration and presents ongoing monitoring and calibration activities during the commissioning.