Table 2 Backgrounds to the 40K geoneutrino e+ signal in LiquidO

From: Probing Earth’s missing potassium using the antimatter signature of geoneutrinos

e+ backgrounds

Source

Expectation

Suppression

IBD(AX) of U and Th geoneutrinos

~1/5 rate of predicted 40K geoneutrinos in K energy interval

Irreducible but measured by IBD(p)

IBD(AX) of reactor antineutrinos

~1/60 rate of predicted 40K geoneutrinos in K energy interval

Irreducible but measured by IBD(p)

β+ decays of naturally occurring 40K in the detector

~10–5 e+ per year per ton

Use of decay energy spectrum to constrain

β+ decays of cosmogenic isotopes

Similar to β+ isotope production in current experiments

Cosmic muon veto and energy spectrum for further suppression

Pair production (e+-e–) by gamma rays (conversion)

Pair production cross section in the [1.022, 1.144] MeV range is ~10–3 times the Compton scattering cross section that dominates in current experiments

Gamma rays make other interactions prior to converting; LiquidO event pattern helps reject

Multiple Compton scattering (fake e+ signal)

e+ signal is still very distinctive compared to gamma-ray-induced single electron recoils

Monte Carlo study of rejection of gamma rays using event pattern and energy flow

  1. The 40K geoneutrino signal is a single e+ that can be identified in LiquidO, as illustrated and described in Fig. 3. All possible backgrounds, including irreducible antineutrinos, true e+ sources and gamma rays converting or faking e+ events, are listed in the table, along with a brief note on how these backgrounds compare and how they might be further suppressed. Further details can be found in the main text.
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