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Low Energy Neutrino Physics AT Nuclear Power Reactors

This presentation reviews research conducted by the TEXONO Collaboration at the Kuo-Sheng Reactor Neutrino Laboratory on studies related to neutrino magnetic moments, coherent scattering, and other programs in low-energy neutrino physics. The collaborative efforts involve various institutions from Taiwan, China, Turkey, India, and the USA. The program focuses on investigating neutrino properties, interactions, and reactor neutrino spectra evaluation. Experimental manifestations and theoretical implications of neutrino magnetic moments and relevant astrophysical bounds are discussed, emphasizing the need for direct experiments to explore fundamental neutrino properties. The TEXONO data analysis and results from magnetic moment searches at the Kuo-Sheng facility are also presented, highlighting the innovative experimental approach and potential significance for advancing neutrino physics research.

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Low Energy Neutrino Physics AT Nuclear Power Reactors

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  1. Henry T. Wong / 王子敬 Academia Sinica / 中央研究院 @ June 2006 Low Energy Neutrino Physics AT Nuclear Power Reactors • Overview : TEXONO Collaboration & Kuo-Sheng Reactor Neutrino Laboratory • Studies on Neutrino Magnetic Moments • R&D projects towards Neutrino-Nucleus Coherent Scattering • Other Related Research Program • Summary

  2. Neutrino Physics at (L~0) Reactor ?? Rationale : • Need neutrino source to do neutrino physics : reactor is a high-flux, understood and controlled source AND free as well !! • oscillation expts.mn0  anomalous n properties & interactions • Experimental neutrino physics has been full of surprise • Worth exploring any experimentally accessible parameter space • May place constraints to interpretation of precision oscillation data • Explore new neutrino sources & detection channels for future studies

  3. TEXONO Collaboration Taiwan EXperiment On NeutrinO Collaboration : Taiwan (AS, INER, KSNPS, NTU) ; China (IHEP, CIAE, THU, NJU) ; Turkey (METU) ; India (BHU) ; USA (UMD) Program: Low Energy Neutrino & Astroparticle Physics • Kuo-Sheng (KS) Reactor Neutrino Laboratory (Taiwan) Neutrino properties & interactions • Yang-Yang Underground Laboratory (S. Korea)[with KIMS Coll.] Dark Matter Searches • Diversified/Non-ReactorProgram • Trace Radiopurity Techniques with AMS • Sonoluminescence ………

  4. Poineering Efforts : “Zero-Background Experiment” ! • KS Expt:1st large-scale particle physics experiment in Taiwan • TEXONO Coll. : 1st big research Coll. % Taiwan & China 

  5. Kuo-Sheng Nuclear Power Plant KS NPS-II : 2 cores  2.9 GW KS nLab: 28 m from core#1

  6. Kuo Sheng Reactor Neutrino Laboratory Front Gate Front View (cosmic vetos, shieldings, control room …..) Configuration: Modest yet Unique Flexible Design: Allows different detectors conf. for different physics Inner Target Volume

  7. Reactor Neutrino Spectra Evaluation… Reactor Operation Data Nuclear Physics

  8. quality Detector requirements mass On-Going Data Taking & Analysis • SM s(ne) • T > 2 MeV • R&D : • Coh. (nN) • T < 1 keV Results : • mn(ne) • T ~ 1-100 keV Reactor Neutrino Interaction Cross-Sections

  9. KS Expt: Period I,II,III Detectors ULB-HPGe [1 kg] CsI(Tl) Array FADC Readout [16 ch., 20 MHz, 8 bit] Multi-Disks Array [600 Gb]

  10. Neutrino Electromagnetic Properties : Magnetic Moments requires mn0 e.g. • a conceptually rich subject ; much neutrino physics & astrophysics can be explored n-osc. : Dmn , Uij 0nbb : mn, Uij , nD/nM • mn: mn, Uij , nD/nM , n  g • fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings ; in principle can differentiate Dirac/Majorana neutrinos • explore roles of neutrinos in astrophysics

  11. Experimental Manifestations • Minimally-Extended Standard Model with nD : mn VERY small many ways to significantly enhance it (nM, WR …..) • study consequences from the change of neutrino spin states in a (astrophysical) medium • 1/T spectral shape in n-e scattering, T is electron recoil energy • Neutrino radiative decays • …………

  12. Astrophysics Bounds/Indications From: • Big Bang Nucleosynthesis degree of freedom • Stellar Cooling via • Cooling of SN1987a vianactive nsterile • Absence of solar ranges of mn(astro) < 10-10 – 10-12mB Complications/Assumptions : • astrophysics modeling (e.g. Solar B-field) • Neutrino properties (e.g nD / nM ; no other anomalous effects) • Global treatment (e.g. effects from matter, oscillations ; interference/competitions among channels ……)

  13. Direct Experiments • using sources understood by independent means : reactor n , accelerator n , n at detector , n-sources (future) • look for 1/T excess due to n-e scattering via mn channel over background and Standard Model processes • reactor n :reactor ON/OFF comparison to filter out background uncertainties • n : account for background spectra by assumptions/other constraints • limits independent of |n>final : valid fornD/nM & diag./tran. moments--no modeling involved • interpretation of results : need totake into account difference in |n>initial

  14. Direct Experiments at Reactors • Search of mn at low energy •  high signal rate & robustness: • mn>>SM [ decouple irreducible bkg  unknown sources ] • T << En ds/dT depends on total fn flux but NOT spectral shape[ flux well known : ~6 fission-n ~1.2 238U capture-nper fission ]

  15. Magnetic Moment Searches @ KS • simple compact all-solid design : HPGe (mass 1 kg) enclosed by activeNaI/CsI anti-Compton, further by passive shieldings&cosmic veto • selection: single-event after cosmic-veto, anti-Comp., PSD • TEXONO data (571/128 days) ON/OFF)[PRL 90, 2003 ; hep-ex/0605006] • background comparable to underground CDM experiment : ~ 1 day-1keV-1kg-1 (cpd) • DAQ threshold 5 keV analysis threshold 12 keV

  16. After-Cut Spectra …….

  17. Combined Analysis with all Information :

  18. Systematic Effects : • Stabilities of Background & Detector Performance

  19. ON/OFF Residual Plot : Limit: mn(ne)< 7.2 X 10-11mB @ 90% CL

  20. Direct Experiments at Reactors

  21. g-n Couplings : Neutrino Radiative Decays

  22. Sensitivity Improvement & Limitations Nn: signal events B : background level m : target mass t : measurement time Scales as: • Nn fn (neutrino flux) & related to T-threshold • T-threshold : e.g. Nnincrease X~3 from 10 keV to 10 eV in Ge (1/T  atomic energy level threshold) • BIG statisticalboost in mncomes from enhancement in fn by, e.g. artificial n-sources, b-beams etc. • BUT: for systematics control, coupled with • low threshold to keepmn >> SM rates • maintain low background level • En~O(1 MeV)T~1 keV mn~SM mn < 10-12mB not practical (by studying n-e scatterings)

  23. Standard Model Cross-Sections: Neutrino-Nucleus Coherent Scattering : • a fundamental neutrino interaction never been experimentally-observed • s~N2applicable at En<50 MeV where q2r2<1 • a sensitive test to Stardard Model • an important interaction/energy loss channel in astrophysics media • a promising new detection channel for neutrinos; relative compact detectors possible (implications to reactor monitoring); &the channel for WIMP direct detection ! • involves new energy range at low energy, many experimental challenges & much room to look for scientific surprises

  24. e.g. at QF=0.25 & 100 eV threshold • Rate ~ 11 kg-1 day-1 • c.f.nN (Ge;1 keV) @ accelerator ~ 0.1 kg-1 day-1 ; • ne-p (water) @ KS ~ 1 kg-1 day-1 Expected Interaction Rates at KS @ different Quenching Factors by-product : T>500 eV gives mn(ne)  ~ 10-11mBat ~ 1 cpd background

  25. “Ultra-Low-Energy” HPGe Prototype • ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation • Prototypes : (I) 5 g ; (II) 4 X 5 g ; (III) 10 g ; (IV) segmented 20g . O(1 kg) can be in multi-array orintegrated form • threshold <100 eV after modest PSD [lowest achieved for bulk radiation detectors] • study feasibilities in nN coherent scattering & Dark Matter searches [ mnsearch a by-product ] 4 X 5 g 5 g

  26. ULE-HPGe Prototype Results PSD Cut Threshold ~ 100 eV • Calibrations by keV lines & “0” from random trigger • Achieved threshold < 100 eV : lowest for bulk radiation detectors ! • Background measurements under way at KS & Y2L

  27. TEXONO  KIMS @ Y2L • Yangyang Lab (Y2L) [700 m of rock overburden] in S. Korea • Install 5 g ULB-ULEGe at Y2L • Study background and feasibility for CDM searches • may evolve into a full-scale (1 kg) CDM experiment Y2L

  28. Sensitivity Plot for CDM-WIMP search with 1 kg ULEGe at 100 eV threshold ………

  29. R&D Program towards Realistic O(1 kg) Size Experiments (both nN & CDM) : • measure & study background at sub-keV range at KS & Y2L ; design of active & passive shielding based on this. • compare performance of various prototypes • devise calibration scheme at sub-keV range • measure quenching factor of Ge with neutron beam • develop advanced PSD techniques to further suppress noise-edge reduce threshold • studying scale-up options ULEGe-detector • Discrete elements Vs segmented Ge • dual readout channels to suppress electronic noise A New Window : “ don’t know what to expect & what are expected ”

  30. 2D Projection • A Possible Design : • 3X3X5 elements @ 20 g each (i.e. 900 g) • Dual readout per element • veto ring  lids

  31. Other Projects at Kuo-Sheng …………….

  32. Nuclear material Fission products Structure material n n rich nuclei －decay EC EC n rich nuclei － decay Stable isotope even-even Stable isotope Electron neutrino emission electron anti-neutrino emission Electron Neutrinos @ Reactor (PRD 72, 2005) • Evaluate ne flux at standard reactors • Derive limits on mnand Gn for ne • Explore ne flux enhancement in loaded reactor (e.g. with Cr) • Study Potential applications : • neNCC cross-section measurements, • q13 • Pu-production monitoring

  33. c.f. ~7.2 /fission Regular Reactor : X 10-4 Loaded Reactor :

  34. Single Crystal QL Vs QR (Raw Data) Z = 0 cm 208Tl 40K 137Cs Region of Interest for SMs(ne) CsI(Tl) Array (~200 kg) : s(ne) Data taking &analysis under way…….. Z =40 cm

  35. Complex analysis later “first & preliminary” results …….. ON/OFF Residual Plot : The best fit of sin2qW : 0.37 ±0.13 at 3-8MeV 0.30±0.22 at 3.5-8MeV + factor of 4+ more data & more sophisticated analysis Goal : 10% measurement

  36. Looking for n-induced 73Ge* Tagging of 73Ge ½- 2g transitions • Event-by-Event background-free tag with PSD • To do : Reactor ON/OFF analysis on the system ~1 s before/after the transition • n-induced events signature: excess in the “ON+before” spectra

  37. Like TEXONO HPGe Reactor Axions Analysis with HPGe data a la… • Reactor core has intense M1 transitions : e.g. 7Li, 91Y, 97Nb etc. • Signature : peak at transition energy at HPGe due to Primakoff conversion

  38. Summary & Outlook Some interesting, at least valid, neutrino physics at reactor Smaller scale  involve exploring new experimental regime  No hints that non-standard picture may show up Not mainstream  Look for surprise • Intellectual fun  Experimental challenge  “Surprises need not be surprising in Neutrino Physics”

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