1. Towards kg-scale Ultra-Low-Energy Ultra-Low-Background Ge Detector
Starting Points (Collaboration ; Laboratories ; Scientific Program)
Potential Physics with ULE-ULB-Ge
Lessons and Experience from ULE-ULB-Ge Prototypes
Status & Plans & Discussions @
Henry T. Wong
Academia Sinica , Taiwan.
Canberra-Eurisys, Lingolsheim, Sept 2006

2. Objectives for this Visit :
Establish stronger collaborating relationships.
US : learn the technologies and future evolution in details
Canberra : understand/comment on our special needs and plans & how we use the detectors
Learn status of segmented 20 g and discuss how to use it optimally for our goals.
Discuss various aspects of possible scale-up to O(1 kg) : how realistic, how much, how long, how to fund …. Etc.
Personal scientific curiosity …..

3. Leading government-funded basic research organization in Taiwan
physical & biological sciences, humanities in ~30 institutes
Like Max Planck Institutes in a centralized campus.
One of the biggest institutes in AS ; ~ 300+ staff with ~40 research faculties
Work on nano-science, biophysics, complexities & nuclear+particle physics

4. 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 ; Axion Searches
Yang-Yang Underground Laboratory (S. Korea) [with KIMS Coll.]
 Dark Matter Searches
Diversified R&D Projects
Trace Radiopurity Techniques with AMS
Sonoluminescence ………

5. Extended collaboration ~30 people
Part of the group at AS
Extended collaboration ~30 people

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

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

8. 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

9. Shielding Structures : Schematics

10. 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
1 counts / kg-keV-day

11. 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]

12. Achieved:
 A 10-keV threshold kg-scale experiment at reactor site with “cpd”-background comparable to underground lab.
Evidence of cosmic-ray activation through various Ga-decays

13. Magnetic Moment Searches : Highlights
simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/CsI anti-Compton, further by passive shieldings & cosmic veto
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
mn(ne) <7.2 X mB (90% CL)
[preliminary]

14. Next Goals:
Develop 1) kg-scale experiment at 2) 100-eV threshold at the 3) same cpd-background level
Scientific subjects: 1) first obseravtion of nN coherent scattering ; 2) Dark Matter searches at low-mass range ; 3) improve on magnetic moments
First choice of Detector Technology : Ge  1) built on existing experience ; 2) LN2 instead of He temperature ; 3) more matured (??) at industry for scale-up.

15. Neutrino-Nucleus Coherent Scattering :
Expected Interaction Rates at different Quenching Factors for Ge
e.g. at QF=0.25 & 100 eV threshold
Rate ~ 11 kg-1 day-1
c.f.
nN @ accelerator ~ 1000 ton-1 yr-1
ne-p KS ~ 1 kg-1 day-1
 nN sensitive region : T < 500 eV
 by-product : T>500 eV gives
mn(ne)  ~ mB at ~ 1 cpd background

16. 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
Expected sensitivity
Y2L

17. Quenching Factor Measurement for Ge at CIAE’s 13 MV Tandem Facility:
Goals for Oct 06 Run :
Get to sub-keV
Improve on present sensitivities

18. “Ultra-Low-Energy” HPGe Prototype
ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation
Prototypes built [Canberra-Meriden] and studied : (I) 5 g at Y2L ; (II) 4 X 5 g at KS ; (III) 10 g at AS
Prototype being built [Canberra-Lingolsheim] : segmented 20 g
Scale-up options to O(1 kg) in multi-array or integrated form (??)
threshold <100 eV after modest PSD

19. N=1 single element (5 g & 10 g) : Schematics

20. 4 X 5 g
N=4 array : Schematics

21. Segmented 20g : Schematics
♥ Under construction at Canberra-Eurisys

23. Auto LN2 Refill system for N=4 array
Segmented 20 g : larger dewar , single reservoir ; prefer AMI-186 Series

24. System Schematic Diagram
Typical signals:
HPGe High gain
(0~9keV)
HPGe Low gain
(0~100keV)
CsI(Tl) channel
(current signal)

25. CAEN VME: 4 Channel 12 bit 40 MHz ADC

26. System configuration Dataset configuration Dataset 1 Dataset 2
Academia Sinica data
Dataset 2
Power Plant Data
FADC sampling rate (MHz)
20 MHz
FADC sampling time (bins / μs)
1800 bins / 90 μs
1424 bins / 71.2 μs
Amp#1
Gain
Shaping time (μs) 80 12
Amp#2
750 6

27. ULEGe Calibration
Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray  random trigger for zero
♥ Would hope to have sub-keV calibration point (HOW ??)

28. PSD I : Correlate two gains & shaping time
sh=6us, high gain
sh=12us, super gain

29. Events near threshold sh=6us, high gain y-axis sh=12us, super gain
x-axis
energy= eV
noise
energy= eV
signal

30. PSD II : Correlate with pre-trigger pulse shapes
sh=6us, super gain
sh=12us, high gain

31. KS events: signal sh=12us, high gain x-axis sh=6us, super gain y-axis
energy=217eV
energy=373eV

32. KS events: noise sh=12us, high gain x-axis sh=6us, super gain y-axis
energy=151eV
energy=177eV

33. ULE-HPGe Prototype Results
PSD Cut
Threshold ~ 100 eV
Calibrations by keV lines & “0” from random trigger
Single channel readout : PSD by two shaping times & gain
Achieved threshold < 100 eV : lowest for bulk radiation detectors ! – at regular background
Background measurements under way at KS & Y2L

34. Intensive studies on sub-keV background
Background Measurements & Comparisons
Intensive studies on sub-keV background
Similar background at KS & Y2L
Apparent difference between 5 g & 1 kg due to scaling with surface area instead, reproduced in simulations
i.e. background can be ~ O(1 cpd) at > 1 keV range for 1 kg ULEGe in compact array form
Intensive studies of sub-keV background under way

35. Background comparison

36. Threshold Vs Background Plots
AS better electronics noise levels
Scale up to compact 1 kg ; understand background source (g/n) ; improved shielding design
Improved PSD ; dual-readout coincidence

37. 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
keep other detector options open

38. 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
1X1 + ring , dual readout prototype available Oct 06.

39. Time Scale & Plans :
To Demonstrate with segmented 20 g : give 100 eV treshold (after all analysis work), project background ~cpd level at eV (with Ge-active-veto)
Can submit proposal for 1-kg ULEGe by then (summer 2007 ??)
Construction can start as soon as end 2007 depending on a) prototype results; b) AS funding approval ; and c) any flexibilities in staging of construction & payment (to be discussed).
Scientific Goals  R&D plans/results were known and viewed with anticipation in the field of neutrino physics
presentations in numerous international conferences [WIN05-Delphi ; TAUP05-Zaragoza ; n06-Santa Fe ; ICHEP06-Moscow ; NDM06-Paris ……]

40. Summary & Outlook Kuo-Sheng Neutrino Lab.:
Established & Operational  Modular & Flexible Design
※ Unique HPGe Low Energy Data 10 keV threshold)
※ Bkg Level ~ Underground CDM Expt.
Results on mn (Gn)  Other Program under way
Future goal : an O(1 kg)+100 eV threshold expt.  observe neutrino-nucleus coherent scattering  perform LE-CDM experiment  improve on magnetic moment sensitivity
R&D program pursued :
optimization of prototype ~100 eV threshold
first background measurement in the 100 eV – 1 keV region
investigate scale-up options
 Open up a New Detection Channel & New Detector Window

41. Some Output from 2006/9/1 Discussions :
Optimization of detector volume constrained by a) perimeter and b) thickness
Constraints : diameter < 85 mm ; thickness < 10 mm
Keen to see how to dual-channel-correlation studies work out
Try studying pulse shapes of raw pre-amp pulse AFTER AC-coupling
Can HV side be a single channel ? i.e. what’re its roles : for PSD or PSD+energy
Minimize length to bring out contacts : i.e. prefer no “inland” channels
Expect new product in 2007 on electrical-cryo-system that can go below liquid nitrogen temperature.