Calibration of the DANSS detector with stopped atmospheric muons and their decays

Calibration of the DANSS detector with stopped atmospheric muons and their decays Gorovtsov Petr, UNIPD & INFN Padova, [email protected] on behalf of DANSS collaboration for Neutrino Telescopes 2025, Padova •Detector of AntiNeutrino based on Solid Scintillator oPlaced under Kalinin Nuclear Power Plant (KNPP) reactor o> 9 × 106Inverse Beta Decay (IBD) 𝝂𝒆+ 𝒑 → 𝒏 + 𝒆+events were accumulated oReactor monitoring during more than 7 years oReactor power is measured by the DANSS with neutrino flux with 1.3% accuracy in 3 days oFission fractions are obtained from positron spectra with 2% accuracy in 2 weeks oThe world's best model independent limits for sterile neutrino search in the Δ𝑚14 2range ∼ 1 𝑒𝑉2, sin22𝜃𝑒𝑒 oIn search for Large Extra Dimensions (LED) DANSS excludes RAA and GA explanations and obtains the strictest limits for some regions in the model independent analysis oOscillation analysis analysis requires precise energy calibration •Detector design oVeto + passive shielding (copper, lead and borated polyethylene) + 50 m of w.e. (building + reactor + spent fuel pools) oDetector is placed on the movable platform →spectra ratio is measured with the same detector →detector & reactor systematics are almost completely reduced o2500 plastic scintillator strips, light collected via wavelength shifting fibers o1 strip connected to 1 SiPM and the group of 50 strips to 1 PMT oThis poster covers only SiPM calibration oStrips are oriented in orthogonal directions so events are reconstructed in 3D oIn total: 1x1x1 m3; 2500 SiPM; 50PMT oScintillator ageing (−0.55%/year in L.Y.) is studied and signals are corrected for it Muon’s track in DANSS. 3D picture is obtained from two 2D projections Reactor power measured with ഥ𝜈𝑒flux and compared with traditional methods used at KNPP I. Alekseev et al., DANSS, Letters to JETP, vol 122, issue 1, page 3, 2025 Exclusion of LED parameters: dominant ED size 𝑎and lightest neutrino mass 𝑚0for normal (left) and inverted (right) mass ordering. Exclusion of sterile neutrino parameters from model independent analysis •Bragg’s curves oRecord signals from every strip as a pair (−𝑙, 𝑑𝐸 𝑑𝑥), where 𝑙–dist. to stop measured in 𝑔/𝑐𝑚2. Fill 2D-histogram with these values oSplit the histogram into slices along 𝑙-axis oFind median losses 𝑑𝐸 𝑑𝑥𝑚𝑒𝑑 in slices over 𝑙 oBragg’s curve –array of points (−𝑙, 𝑑𝐸 𝑑𝑥𝑚𝑒𝑑) oCompare Bragg’s curves obtained from MC and Data •DANSS calibration is done with 𝛽-decays of 12𝐵 •Selection criteria for IBD events rely on minimal energy of gamma burst from 𝑛which is correlated with energy scale fixed by calibration. •Potentially important source of systematic uncertainty for oscillation analysis – relative efficiency in Top (10.9 m to the reactor) and Bottom (12.9 m to the reactor) positions •This calibration was done separately for Top and Bottom •Position-wise corrections are made to: •average temperature (affects SiPM efficiency) •fuel evolution (affects ഥ𝜈𝑒flux) After the correction IBD rate in Top and Bottom differs by 0.4% which is used as an estimate of systematic 𝜇stop point MeV •Muon decay selection oDecay event in 1−7𝜇𝑠 window after muon oFull energy > 5 𝑀𝑒𝑉 o≥ 2 hits in strips neighbour to the strip of the muon stop oMuon stop point is in the inner cube with side 0.5 of the detector size •Stopped muon selection oSignal in upper layer and no signal in 3 bottom layers and side strips oMuon is almost vertical (𝜃 < 10𝑜) o> 6 strips in both XZ and YZ planes oDead channels are taken into account in both Data and MC oDecay in 1 − 7 𝜇𝑠 window MeV 𝜃 •𝐾𝐸from stopped muons and their decays coincide but ≈ 1% bigger than DANSS calibration with 12𝐵 •Calibration in Top and Bottom positions are in perfect agreement •Calibration is very stable during 9 years of operation, down to + 0.02 %/𝑦𝑒𝑎𝑟 •Bragg’s curve is sensitive to •𝐾𝐸energy scale •𝐾𝐵Birks coefficient •𝐾𝐶ℎ - Cherenkov light intensity •𝐾𝐷thickness of strip’s coating •All parameters but 𝐾𝐸were fixed in previous studies with Bragg’s curves •Michel spectrum is sensitive to •𝐾𝐸energy scale •𝐾𝑠additional smearing of spectrum •Good MC-Data correspondence is achieved without additional smearing See also the talk “Searches for physics beyond SM at DANSS” at 02.10, 10:10 Spazio 35 Cultural center San Gaetano I. Alekseev et al, (DANSS), Phys. Let. B, vol 866, 139575, 2025 2-3 days/point 7 days/point I. Alekseev et al, (DANSS), Phys. Let. B, vol 866, 139575, 2025 ∼ 1 week in October 2019 ∼ 3 days in October 2019 I. Alekseev et al., DANSS, JINST, vol 19, April, 2024