Speaker
Description
The Jiangmen Underground Neutrino Observatory (JUNO) is the world’s largest liquid scintillator experiment that detects neutrinos mainly via inverse beta decay (IBD) with protons. It is designed to determine the mass hierarchy of neutrinos using 20 kton of liquid scintillator (LS) located 52.5 km away from two nuclear power plants. It took approximately 6 months to fill LS from February 2025, after that in August JUNO started data-taking and measured neutrino oscillation parameters Δm_{21}^{2} and sin^{2}θ_{12} to an unprecedented precision with two months of data.
The ^{214}Bi-^{214}Po decay is a type of important time-correlated events in JUNO detector. It is mainly generated from decay chains of the 222Rn dissolved in LS during filling phase and the intrinsic 238U contamination of LS. Under secular equilibrium with 222Rn, the decay rate of 214Bi-214Po will drop with ^{222}Rn’s lifetime (5.51 days). Under secular equilibrium with 238U, the decay rate of ^{214}Bi-^{214}Po remains constant, revealing the level of 238U in LS. The high population of short-term ^{214}Bi-^{214}Po events from 222Rn produces the long-existing 210Pb background that can impact JUNO’s sensitivity in both reactor and solar neutrino analysis. Therefore, a careful Rn control during LS filling phase is requisite. The low population of long-term 214Bi-214Po events from 238U produces β-⍺ coincidence background to neutrino oscillation analysis, considering ⍺ scattering with proton can lead to a higher quenching energy that enters n-H capture energy range of IBD signals. Consequently, a proper estimation of this background in reactor antineutrino oscillation analysis is also crucial.
In this poster, the strategies of Rn monitoring and control during the LS filling phase will be introduced, including the evaluation on Rn leakage rates of several periods. On the other hand, an estimation of ^{214}Bi-^{214}Po (β-⍺) background contribution in reactor antineutrino oscillation analysis of JUNO is presented in details.