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First observation of reactor anti-neutrinos via coherent scattering with CONUS+ Christian Buck, MPIK Heidelberg Neutrino Telescopes, Padova, Oct 1st 2025
Coherent elastic neutrino nucleus scattering 1 M. Cadeddu et al 2023 EPL 143 CEvNS advantages: • NC interaction ==> all flavors • No reaction threshold • “Small” neutrino detectors Challenge: tiny recoil E
Neutrino sources for CEvNS studies 2 Reactor • Pure electron antineutrino flux • E < 10 MeV ==> form factor ~1 Pion decay-at-rest • Different neutrino flavors • E > 10 MeV ==> form factor <1 Coherence TEXONO, arXiv2502.20007
Implications 2 Nuclear physics Dark matter (“neutrino floor”) BSM physics Astrophysics 𝛑-decay at rest Reactor neutrinos https://science.osti.gov/-/media/ascr/ascac/pdf/meetings/mar03/Mezzacappa.pdf K. Patton et al., PRC 86, 024612 (2012) J.Tang et al., PRD 108, 062004 (2023) M. Cadeddu et al., EPL 143 (2023) 3
CEvNS worldwide 4 First observation: COHERENT in 2017 (CsI at SNS)
CONUS Collaboration N.Ackermann, H.Bonet, C.Buck, J.Hakenmüller, J.Hempfling, G.Heusser, M.Lindner, W.Maneschg, S.Mertens, K.Ni, T.Rink, E.Sanchez Garcia, H.Strecker Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany K.Fülber, R.Wink Preussen Elektra GmbH, Kernkraftwerk Brokdorf (KBR), Germany M.Rank, I.Stalder, J.Woenckhaus Kernkraftwerk Leibstadt AG (KKL), Switzerland 5
Concept Strong source Low background Low threshold Ge spectrometers Shield Nuclear power plant (Leibstadt, CH, KKL) 6
The CONUS Ge detectors 7 High-purity PPC Ge detectors (4x) Each 1 kg mass Electrical cryo-cooling Low threshold, high E resolution
The CONUS+ shield 8 ~ 10 tons, 1.65 m3 Low radioactivity Pb Borated PE Active muon veto Flushing with air bottles (Rn removal) Steel structure (earthquake-resistant) ~ 4 orders of magnitude background reduction
Signal expectation 15 Detector Threshold Live time Predicted events C2 180 eV 117 d 96 ± 16 C3 160 eV 110 d 135 ± 23 C5 170 eV 119 d 116 ± 20 Prediction uncertainties Energy 14.1 % Quenching 7.3% Reactor flux 4.6% Crosssection 3.2% Active mass 1.1% Trigger efficiency 0.7%
Global picture 16 Experiment Source Target Signal Data/SM COHERENT Accelerator Cs 306±20 0.90±0.14 COHERENT Accelerator Ar 140±40 1.22±0.49 COHERENT Accelerator Ge 21±7 0.59±0.26 XENONnT Sun (8B) Xe 11±4 0.90±0.66 PandaX-4T Sun (8B) Xe 3.5±1.3 1.25±0.69 CONUS+ Reactor Ge 395±106 1.14±0.36 CONUS+: lowest neutrino energy, highest rate for single element M.Atzori Corona et al., PRD 112 (2025) 1, 015007 CONUS+
BSM studies 17 Preliminary! A.Chattaraj et al., arXiv 2501.12441 (2025) Non-standard interactions Electromagnetic properties Light mediators M.Atzori Corona et al., PRD 112 (2025) 1, 015007
Outlook 18 3 detectors replaced by larger mass crystals (2.4 kg) Run-2 started early 2025 Include pulse shape discrimination Improve precision Technology scalable 100 kg >100000 𝜈/year 100 120 140 160 180 200 220 240 ] ee Energy threshold [eV 0 2000 4000 6000 8000 10000 12000 14000 16000 Signal prediction [counts/year] CONUS: 3.74 kg, Run-5 CONUS+: 3.74 kg, Phase-1 CONUS+: 9.20 kg, Phase-2
Summary High cross-section of CEνNS ==> compact neutrino detectors CONUS+: HPGe detectors at 20.7 m from reactor core Mainly cosmic background events: reactor power uncorrelated! First CEvNS detection at nuclear reactor (3.7 sigma) Result consistent with theoretical models and predictions Run-2 with increased mass has started
