Verification of the calibration method for the boundary effect in JUNO

Jiangmen Underground Neutrino Observatory (JUNO) is constructed to probe multiple physics goals, including determining the neutrino mass ordering (MO), measuring solar neutrinos, detecting supernova neutrinos, etc. A large Liquid Scintillator (LS) detector with a high energy resolution is being built to determine the neutrino MO within 6-year of data taking. To accomplish this goal, a calibration complex has been designed. Concerning the energy leakage near the LS boundary, a Guide Tube Calibration System (GTCS) will be deployed on the outer surface of the JUNO central detector to help better understand the boundary effect. A fitting algorithm has been presented during the design of GTCS considering the overlap of full-energy peak and Compton tail. In this paper, we verify the fitting algorithm experimentally, using a radioactive source in the Daya Bay experiment. The maximum bias of full-energy peak for the experiment at Daya Bay is less than 1.0% even if a change of ±20.0% in acrylic density was assumed. Besides, the tuned acrylic density is applied in JUNO GTCS simulation. The maximum uncertainty estimation of GTCS energy response in total is 0.52%, satisfying the JUNO GTCS requirement which is 1.0%.