Physics potential of searching for 0vββ decays in JUNO

Abstract: In the past few decades, numerous searches have been made for the neutrinoless double-beta decay (0vββ) process, aiming to establish whether neutrinos are their own antiparticles (Majorana neutrinos), but no 0vββ decay signal has yet been observed. A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass. We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory (JUNO) to improve the sensitivity to 0vββ up to a few meV, a major step forward with respect to the experiments currently being planned. JUNO is a 20 kton low-background liquid scintillator (LS) detector with 3%E(MeV) energy resolution, now under construction. It is feasible to build a balloon filled with enriched xenon gas (with ¹³⁶Xe up to 80%) dissolved in LS, inserted into the central region of the JUNO LS. The energy resolution is ～1.9% at the Q-value of ¹³⁶Xe 0vββ decay. Ultra-low background is the key for 0vββ decay searches. Detailed studies of background rates from intrinsic 2vββ and ⁸B solar neutrinos, natural radioactivity, and cosmogenic radionuclides (including light isotopes and ¹³⁷Xe) were performed and several muon veto schemes were developed. We find that JUNO has the potential to reach a sensitivity (at 90% C. L.) to T_1/2^0vββ of 1.8×10²⁸ yr (5.6×10²⁷ yr) with ～50 tons (5 tons) of fiducial ¹³⁶Xe and 5 years exposure, while in the 50-ton case the corresponding sensitivity to the effective neutrino mass, m_ββ, could reach (5-12) meV, covering completely the allowed region of inverted neutrino mass ordering.