Study of radon background in the SuperNEMO demonstrator • 𝜷𝜷𝟎𝝂Source foil: 𝟔. 𝟏𝟏𝒌𝒈of 82𝑺𝒆 with 𝑄𝛽𝛽~ 3 𝑀𝑒𝑉 • Tracker: 2034 Geiger cells • Calorimeter: 712 Optical Modules (OMs : Plastic scintillators + PMTs) • Copper coil for magnetic field 𝑩 Anti-radon strategy Anti-radon strategies: • Material screening for radiopurity ➔very low Rn emanation • J-Trap facility ➔ultra high Rn purification of the gas (He+Ar) • Anti-Rn tent ➔Buffer volume against the air from the LSM lab • Anti-Rn factory ➔to inject Rn-free air in the tent 222Rn decay to 214𝐁𝐢(Qβ−= 3.272 MeV) →background for 0νββ search Measuring Rn activity ⟺measuring BiPo activity Golden 214Bi-214Po channel: 1 electron + 1 delayed alpha (T214Po = 164 μs) Efficiency selection of 3.1% From 106 events simulated on the surface of the grounds wires Objectives • To optimize the BiPo selection criteria with high statistics • To study the spatial radon uniformity in the detector • To study the radon residence time in the detector Top view of the e- vertices distribution from the selected BiPo events →Spatial Rn uniformity in the bulk of the tracker →Small side effects and left-right asymmetry under study → Radon and the tracker gas mixture have the same flow dynamics Real BiPo event Time between 𝒆−𝐚𝐧𝐝 𝜶 →Increasing the gas flow by a factor 2 decreases the BiPo rate by a factor 𝐑≈2 as expected SuperNEMO Demonstrator • Goal of SuperNEMO : to search for 0𝜈ββ process with 82Se (Qββ~ 3 MeV) • Sensitivity: T1/2 0ν > 5.7 × 1024 years (17.5 kg.y exposure with 82Se ) • Able to track and measure electron energy independently • Data taking in autumn 2024 Measuring radon activity with 214Bi-214Po decay events Radon background Dedicated radon injection runs Antoine Lahaie, Mathis Granjon, Frédéric Perrot, Yegor Vereshchaka, on behalf of the SuperNEMO collaboration Radon source • Emanation rate: 95 ± 5 Rn atoms per second • Injected in the tracker at 5 L.min-1 Two Rn measurements performed at 5 and 10 L.min-1 c:-( c:-( Ar He Alcohol J-trap Emanation Diffusion ~ 0.15 mBq. m−3 ~ 30 mBq. m−3 Gas mixture Anti-radon factory Laboratory air ~ 30 Bq. m−3 Rn-free air Anti-radon tent New Radon activity updated soon with anti-radon factory, gas purification and nominal gas flow at 20 L.min-1, stay tuned ! • 58 h of Rn background measurement in March 2024 at different gas flow →Consistent with the expected value: →Radon (Rn) is the main background in the tracker Gas + Rn 𝑅= 2.3 ± 0.2 • Electron identification: ➢1 OM triggered ➢≥ 1 associated Geiger cell near the OM ➢Temporally correlated with the OM • Alpha identification: ➢≥ 2 close Geiger cells triggered ➢Delayed alpha below 1.6 µs after electron ➢Short track (≤ 12 Geiger cells ) (He + Ar gas)  Vertex OM Electron Alpha Signal Background noise selection Additional BiPo selection: 82Se source foil OM 𝜶 𝒆− ➢See SuperNEMO poster #451 Electron energy >300 keV e−/α vertex distance in xy plane ≤6 cm e−/α vertex distance on z axis ≤10 cm Delay between α and e−track [300-1600] µs τeff fit = 1.43 ± 0.14 days Measurement of the Rn residence time with gas flow at 5 L.min-1 τeff = 1 ϕ V + 1 τ = 1.54 days Gas only T = 168 ± 8 μs →fully consistent →First Rn background activity in current operation mode at 10 L.min-1 : [10-15] mBq.m-3 ✓ ✓ #41