 TEXONO Collaboration & Kuo-Sheng Laboratory & Program Overview  Results on Neutrino Magnetic Moments, Reactor Electron Neutrinos and Reactor Axion Search  Future Direction - Ultra-Low Energy Detectors for Neutrino- Nucleus Coherent Scattering & Dark Matter Searches  Outlook. Henry T. Wong / 王子敬 Academia Sinica / 中央研究院 November 2007 Hightlights and Status of the TEXONO Research Program on Low Energy Neutrino & Dark Matter Physics KIMS-TEXONO Workshop Seoul National

TEXONO Collaboration Collaboration :  Taiwan (AS, INER, KSNPS, NTU,NCU,NCCU)  China (IHEP, CIAE, THU, NJU, NKU)  Turkey (METU)  India (BHU) + Close Partnership (KIMS Collaboration in S. Korea) Taiwan EXperiment On NeutrinO Poineering Efforts : “Zero-Background Experiment” !  KS Expt: 1 st large-scale particle physics experiment in Taiwan  TEXONO Coll. : 1 st big research Coll. % Taiwan & China

 Need neutrino source to do neutrino physics : reactor is a high-flux, understood and controlled source  AND free as well !!  oscillation expts.  m  0  anomalous 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 Neutrino Physics at (L~0) Reactor ?? Rationale :

Kuo-Sheng Nuclear Power Plant KS NPS-II : 2 cores  2.9 GW NPS-IV

 28 m from 2.9 GW  Shallow depth : ~30 meter-water-equivalent  Reactor Cycle : ~50 days OFF every 18 months Kuo Sheng Reactor Neutrino Laboratory Front Gate

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

FADC Readout [16 ch., 20 MHz, 8 bit] ULB-HPGe [1 kg] CsI(Tl) [200 kg] Multi-Disks Array [600 Gb] KS Laboratory : Detectors ULE-ULB-HPGe Prototype [20 g]

Reactor Neutrino Spectra Evaluation… Nuclear Physics Reactor Operation Data

R&D :  Coh. ( N)  T < 1 keV Completed Results :   ( e ) : T~1-100 keV  Axions : T ~ keV-MeV On-Going Data Taking & Analysis  SM  ( e)  T > 2 MeV Reactor Neutrino Interaction Cross-Sections massqualityDetector requirements 1 counts / kg-keV-day Threshold ~ 100 eV

Research Program of TEXONO :  Search of Neutrino Magnetic Moments [this talk]  Studies of Reactor Electron Neutrino [this talk]  Search of Reactor Axions [this talk]  Measurement of neutrino-electron scattering cross- sections (i.e. sin 2  W at MeV range) with CsI(Tl) crystals [M.Deniz’s talk]  Studies of possible neutrino induced nuclear transitions in Ge & CsI [F.K.Lins’ talk]  Measurement of Trace-Radiopurity with Accelerator Mass Spectrometry [Results Published on I129, K40; Omitted]  Sonoluminescence [F.K. Lin’s talk]

Future Direction [This+H.B.Li’s+S.K.Lin’s talk]:  Open new detection channel and detector window down to 100 eV  testing “ULEGe” prototypes at AS+KS+Y2L  sub-keV Quenching Factor measurements at CIAE  Physics Goals:  First observation of neutrino-nucleus coherent scattering at KS  Dark Matter Searches at low-WIMP-mass region at Y2L  Improvement on Neutrino Magnetic Moment sensitivities  Expect ready for a major experiment with ~1 kg scale detector at [scale : O(1 MUSD )]

Neutrino Electromagnetic Properties : Magnetic Moments e.g. requires m  0  a conceptually rich subject ; much neutrino physics & astrophysics can be explored -osc. :  m , U ij 0  : m , U ij, D / M  : m , U ij, D / M,   fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings ; in principle can differentiate Dirac/Majorana neutrinos  explore roles of neutrinos in astrophysics

Magnetic Moment KS  simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/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 ; PRD 75, 2007   background comparable to underground CDM experiment : ~ 1 day -1 keV -1 kg -1 (cpd)  DAQ threshold 5 keV analysis threshold 12 keV

Limit:   e  < 7.4 X  90% CL ON/OFF Residual Plot :

Search of  at low energy  high signal rate & robustness:   >>SM [ decouple irreducible bkg  unknown sources ]  T << E  d  /dT depends on total  flux but NOT spectral shape [ flux well known : ~6 fission-  ~ U capture- per fission ] Direct Experiments at Reactors

 Couplings : Neutrino Radiative Decays

First exploration of electron-neutrino production at reactors ….

Electron Reactor (PRD 72, 2005) Nuclear material Fission products n rich nuclei Stable isotope Structure material n  － decay  －  decay EC even-even Electron neutrino emission electron anti- neutrino emission  Evaluate e flux at standard reactors  Derive limits on  and  for e  Explore e flux enhancement in loaded reactor (e.g. with Cr)  Study Potential applications :  e NCC cross-section measurements,   13  Pu-production monitoring

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

Exploration of possible axion emission at reactor …..  Idea : Axions can be emitted in gamma-decays AND the power reactor is THE most powerful terrestrial radioactivity source. PRD 75 (2007)

 Production:  Detection:  Experimental Search :

Results: Improved laboratory limits on g aee for Br a >10 -9 Exclude DFSZ/KSVZ Models for axion mass eV

“Ultra-Low-Energy” HPGe Detectors  ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation  Prototypes built and studied :  5 Y2L  4 X 5 KS/Y2L  10 AS/CIAE  segmented 180 AS/KS  Being built : 500 g single element  Physics for O[100 eV threhold  1 kg mass  1 cpd detector] :  N coherent scattering  Low-mass WIMP searches  Improve sensitivities on   Implications on reactor operation monitoring  Open new detector window & detection channel available for surprises

ULEGe-Prototype built & being studied : 5 g 10 g 4 X 5 g Segmented 180 g with dual readout

 measure & study background at sub-keV range at KS & Y2L ; design of active & passive shielding based on this.  compare performance and devise event-ID (PSD & coincidence) strategies of various prototypes  devise calibration & efficiency evaluation schemes applicable to sub-keV range  measure quenching factor of Ge with neutron beam  study scale-up options ULEGe-detector  Keep other detector options open R&D Program towards Realistic O(1 kg) Size Experiments (both N & CDM) :

Sensitivity Plot for CDM- WIMP direct search for 100 eV threshold detector [First Results : LHB’s talk] Low (<10 GeV) WIMP Mass / Sub-keV Recoil Energy :  Not favored by the most-explored specific models on galactic- bound SUSY-neutralinos as CDM ; still allowed by generic SUSY  Solar-system bound WIMPs require lower recoil energy detection  Other candidates favoring low recoils exist: e.g. non-pointlike SUSY Q-balls.  Less explored experimentally

Quenching Factor Measurement for Ge at CIAE’s Neutron Facilities: Goals for Dec 07 Runs :  Use actual ULEGe 100-eV detector  Use lower energy neutron beam with a pulsed-LE tandem With 13 MV Tandem

Detector Scale-up Plans:  500-g, single-element, modified coaxial HPGe design, inspired by successful demonstration of Chicago group (nucl-ex/ )  Position-sensitive from drift-profile pulse shape  Dual-electrode readout and ULB specification  Being prepared, available first-half SS SS p

Scale up to compact 1 kg ; understand background source (  /n) ; improved shielding design Improved PSD ; dual-readout coincidence Road Map ……

 An O[100 eV threshold  1 kg mass  1 cpd detector] has interesting applications in neutrino and dark matter physics, also in reactor monitoring  Open new detector window & detection channel : potentials for surprise  Mass Scale-Up: recent demonstration of realistic design  Threshold – ~300 eV at hardware level, intensive studies on software techniques to aim at ~100 eV, & on their stabilities and universalities  Prototype data at reactor already provide competitive sensitivities for WIMP search at mass<10 GeV.  Sub-keV Background understanding and suppression – under intensive studies State-of-the-Art(Science)

 TEXONO Collaboration:  Built-Up from Scratch & Maturing  Kuo-Sheng Neutrino Lab.:  Established & Operational  Modular & Flexible Design  Physics Data Taking since June 01 ※ Unique HPGe Low Energy Data ※ Bkg Level ~ Underground CDM Expt  Results published on    , reactor e & axions  Diversified Program in Parallel Main Thrust on  ~200 kg CsI(Tl) [  ( e) …]  ULEGe: for  coh ( N) + CDM Search Summary & Outlook