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T: Fachverband Teilchenphysik

T 87: Neutrino Physics V

T 87.1: Talk

Friday, March 20, 2026, 09:00–09:15, AudiMax

Position and Energy Reconstruction in OSIRIS — Thilo Birkenfeld, •Elisabeth Neuerburg, Achim Stahl, and Christopher Wiebusch — RWTH Achen

During the filling of the Jiangmen Underground Neutrino Observatory (JUNO) in 2025, the Online Scintillator Internal Radioactivity Investigation System (OSIRIS) monitored the radiopurity of the liquid scintillator (LS). OSIRIS has 64 20''-PMTs surrounding a cylindrical acrylic vessel holding 20-ton batches of LS. Uranium and Thorium impurities are estimated by counting the Bismuth-Polonium coincidence occurring in both decay chains, identified using time, distance, and energy cuts. The position of an event is reconstructed using a maximum-likelihood estimation, with Lookup Tables to calculate the expected amount of light. The energy is reconstructed from the event's position and the amount of light detected. The resolutions are estimated from simulation data and cross-checked against calibration data obtained by lowering a multi-gamma source into the vessel. In this talk, the position and energy reconstruction methods in OSIRIS and their respective performances are presented.

Keywords: JUNO; OSIRIS; liquid scintillator; position reconstruction; energy reconstruction