Test results of the TAO prototype detector with Co-60 and cosmic muon

The Jiangmen Underground Neutrino Observatory (JUNO) aims to determine the neutrino mass ordering. As a satellite experiment of JUNO, the Taishan Antineutrino Observatory (TAO) is designed to precisely measure the reactor antineutrino energy spectrum at a near site, providing essential reference data for JUNO. TAO represents a novel cryogenic liquid scintillator experiment, utilizing Silicon Photomultipliers (SiPMs) for photon detection and operating at -50∘C to suppress SiPM dark noise. A full-size prototype of the central detector of TAO (approximately 2% SiPMs installed) was assembled before its final deployment to the power plant. This paper presents the test results of the prototype using a Co-60 source at -50∘C, and using the surface flux of ground cosmic muons in the warm-up phase of the detector. The detector simulation software of TAO was adapted to the configuration of the prototype and the Monte Carlo prediction shows good agreement with the Co-60 data. A mild variation of the detector response was observed after correcting the temperature effect of the SiPM performance with the cosmic muon data.