1. 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
Henry T. Wong / 王子敬
Academia Sinica / 中央研究院 @
June 2006

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. Program: Low Energy Neutrino & Astroparticle Physics
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-Reactor Program
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 n Lab: 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

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

10. 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]

11. 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

12. 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
…………

13. Astrophysics Bounds/Indications
From:
Big Bang Nucleosynthesis degree of freedom
Stellar Cooling via
Cooling of SN1987a via nactive  nsterile
Absence of solar
ranges of mn(astro) < – mB
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 ……)

14. 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 for nD/nM & diag./tran. moments -- no modeling involved
interpretation of results : need to take into account difference in |n>initial

15. 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  ~ U capture-n per fission ]

16. Magnetic Moment Searches @ 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 ; hep-ex/ ]
background comparable to underground CDM experiment :
~ 1 day-1keV-1kg-1 (cpd)
DAQ threshold 5 keV
analysis threshold 12 keV

17. After-Cut Spectra …….

18. Combined Analysis with all Information :

19. Systematic Effects :
 Stabilities of Background & Detector Performance

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

21. Direct Experiments at Reactors

22. g-n Couplings : Neutrino Radiative Decays

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

24. Neutrino-Nucleus Coherent Scattering :
Standard Model Cross-Sections:
a fundamental neutrino interaction never been experimentally-observed
s~N2 applicable 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

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

26. “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 or integrated form
threshold <100 eV after modest PSD [lowest achieved for bulk radiation detectors]
study feasibilities in nN coherent scattering & Dark Matter searches [ mn search a by-product ]
4 X 5 g
5 g

27. 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

28. TEXONO  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

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

30. 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 ”

31. 3X3X5 elements @ 20 g each (i.e. 900 g) Dual readout per element
A Possible Design :
3X3X5 20 g each (i.e. 900 g)
Dual readout per element
veto ring  lids
2D Projection

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

33. Electron neutrino emission electron anti-neutrino emission
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 ne flux at standard reactors
Derive limits on mn and 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

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

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

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

37. 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

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

39. 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”