1. Searching for the neutrino magnetic moment at the Kuo-Sheng nuclear power plant
Outline
1. Introduction & Overview
2. The experiment result
3. Future
H. B. Li 李浩斌
Department of Physics,
Academia Sinica.

2. Neutrino Radiative Decay (Gn):
scattering mn
n with mass
 possible niL njR + g vertices
Experimental Probe:
 Study ne + e-  nX + e-
 Focus on low recoil energy
※ sm  T–1
※ decouples SM “background”
[ ……… LE reactor f(ne) not accurately known]
 Look for Excess in Reactor ON/OFF
Neutrino Radiative Decay (Gn):
 sm & Gn related:
 same vertices – real g for Gn
Electron Recoil Spectra

3. PDG Limit : 1.5 X mB
(from SK spectral shape)
an allowed solution for the solar neutrino data (before KamLAND)

4. Kuo-Sheng Nuclear Power Plant
KS NPS-II :
2 cores X 2.9 GW
KS n Lab:
28 m from
core#1

5. ULB-HPGe + Anti-Comptons
KS Expt. : Period I Configuration
Period I : June 01 – April 02 (60 days OFF)
Shielding & Veto [one side]
ULB-HPGe + Anti-Comptons
CsI(Tl) Array (46 kg)

6. KS Expt. : Period I Detector
ULB-HPGe [1 kg]
CsI(Tl) [46 kg]
FADC Readout
[16 ch., 20 MHz, 8 bit]
Multi-Disks Array [600 Gb]

7. HPGe data Data Volume: HPGe Performance: Analysis:
 Total Live Time 196/52 days ON/OFF
HPGe Performance:
 kg mass
 0.4 keV RMS at 10 keV
 5 keV threshold [Unique Data]
 Range of O(1 cpd) [counts kg-1 day-1 keV-1]
background c/f Dark Matter expt.
Analysis:
 Cosmic Veto (5 ms gate)
 Anti-Compton (Well+Base detectors)
 Pulse Shape Disc. (veto elect. noise, accidentals)

8. Background and spectrum
Low background detector
20/keV day
+veto
1/keV day
On-off subtraction
O(0.01) /keV day
10.37 keV peak decaying

9. spectrum Uncertainty(E>3MeV) : 5% Uncertainty(E<3MeV) : 30%
Solid curve : fission, flux =
Dot curve : fission + neutron capture, flux =

10. Efficiency and systematic error
Event Selection Suppression Efficiency
Raw Data
Anti-Compton
Cosmic-Ray Veto
Pulse Shape Analysis
Combined Efficiency
Source Uncertainties
DAQ Live Time ON/OFF <0. 2% <0.30
Efficiencies for magnetic scattering <0.2% <0.01
Rates for magnetic scattering %
SM background subtraction %
Combined Systematic Error <0.4

11. Spectra & Residual Based on 196/52 days of Reactor ON/OFF data
No anomalous structures or residuals

12. Result Fit OFF spectra to fOFF Fit ON spectra to
E/keV fOFF c2/dof
12-61 p /96
Fit ON spectra to
fOFF + fSM + k2 fMM [10-10 mB]
[using best-fit values of (fOFF;dfOFF)]
Fit Results c2/dof = 48/49 ):
k2 = -0.5  1.4 (stat.)  0.4 (sys.)
Limits derived :
mn < 1.3 (1.0) X mB @ 90(68)% C.L.
Improvement in Period 2:
 4p anti-Compton coverage
 improved inner shielding
 Aim of analysis threshold: ~ 5 keV
 study “ultra-low” energy Ge prototype [threshold : eV]
Residual Plot

13. Reactor Sensitivities

14. Summary Best published limit. Only experiment at 10 keV range.
Background level O(1 cpd) [counts kg-1 day-1 keV-1]
Comparable to underground CMD experiment.
Flexible design.
Upgrade to 186 kg of CsI(Tl).
Improve anti-Compton detector.
Improve trigger system and electronic.
Improve the measurement of cosmic veto time.

15. “New Limits on Neutrino Magnetic Moment from the Kuo-Sheng
Reactor Neutrino Experiment”, hep-ex/ ,
To be published in Phys. Rev. Lett.