Upgrade of OSIRIS for Future Liquid Scintillator Studies

Understanding the internal radioactive background contributions in its 20 kiloton liquid scintillator (LS) target is essential for the success of the JUNO reactor neutrino experiment. OSIRIS is a 20-tonne radiopurity detector at the end of the JUNO LS purification chain. It will screen 1/10 of the LS during JUNO filling and verify that its internal radiopurity requirements of are met. Once filling is complete, OSIRIS, in combination with the existing LS purification infrastructure, will serve as an excellent testbed for various types of LS studies and, in particular, for the development of JUNO’s future physics programme. Scenarios considered so far range from long-term LS stability or double beta decay isotope loading tests to stand-alone precision measurements of the solar 𝑝 𝑝 neutrino flux. To maximise the results of such measurements, cost-effective improvements to the OSIRIS detector are needed. For example, to improve the uniformity of light collection, the cylindrical photodetector configuration will be changed to a spherical one. Light collection will be improved by adding light concentrator cones and additional PMTs. The addition of external shielding will help to suppress the external gamma-ray background in the central volume of the detector. This paper discusses in more detail the planned improvements and physics cases for the OSIRIS upgrade.