TAO Conceptual Design Report: A Precision Measurement of the Reactor Antineutrino Spectrum with Sub-percent Energy Resolution

The Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) is asatellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). Aton-level liquid scintillator detector will be placed at about 30 m from a coreof the Taishan Nuclear Power Plant. The reactor antineutrino spectrum will bemeasured with sub-percent energy resolution, to provide a reference spectrumfor future reactor neutrino experiments, and to provide a benchmark measurementto test nuclear databases. A spherical acrylic vessel containing 2.8 tongadolinium-doped liquid scintillator will be viewed by 10 m^2 SiliconPhotomultipliers (SiPMs) of >50% photon detection efficiency with almost fullcoverage. The photoelectron yield is about 4500 per MeV, an order higher thanany existing large-scale liquid scintillator detectors. The detector operatesat -50 degree C to lower the dark noise of SiPMs to an acceptable level. Thedetector will measure about 2000 reactor antineutrinos per day, and is designedto be well shielded from cosmogenic backgrounds and ambient radioactivities tohave about 10% background-to-signal ratio. The experiment is expected to startoperation in 2022.