Commissioning of COHERENT D2O Module 2

The COHERENT collaboration made the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) by employing neutrinos produced by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The uncertainty of the neutrino flux generated from the SNS is on the order of 10% making it one of COHERENT's most dominant systematic uncertainties. To address this issue, a heavy water (D2O) detector has been designed to measure the neutrino flux through the well-understood interaction of electron neutrinos with deuterium. The D2O detector is composed of two identical modules designed to detect Cherenkov photons generated inside the target tank, with Module 1 containing D2O as the target and Module 2 containing H2O for comparison and background subtraction. We also aim to make a measurement of the cross section of the charged-current interaction between the electron neutrino and oxygen, providing valuable insight for supernova detection in existing and future large water Cherenkov detectors. Module 1 was successfully commissioned in summer 2023, and Module 2 is undergoing commissioning in summer 2025. In this presentation, we will describe the design and technical details during the assembly of Module 2, report on its commissioning progress, and share a preliminary background study between Module 2 (H₂O) and Module 1 (D₂O).