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Low Energy Neutrino Physics AT Nuclear Power Reactors

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

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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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