1. CsI Compton Veto Detector for A low Mass WIMP Experiment
He Dao
University
23 Oct 2004

2. Content Introduction of our low mass wimp experiment
Structure of CsI detector
Some test and conclusion
plan

3. Status of WIMP detection
The thresholds are
a few keV
Corresponding to
the ~10GeV mass
limit measurable
This is the gotten results. Some projections show very promising and more stringent results.

4. CRESST: lowest threshold
Cryogenic bolometer
262g Sapphire detector
The lowest threshold
gotten until now:
500keV

5. Our Idea
Using low-threshold detector to “find” low-mass WIMP

6. Our detector 5g Ge detector Shielding
Until now, purest material is Germanium. And Lowest background has been achieved by Ge detector.

7. Background Control Cosmic Ray: Underground lab Material background:
purest material: Ge
Other particles:
Multi-layer shielding:
Pb, Cu, CsI veto detector
PSD(Pulse Shape discrimination)
Until now, purest material is Germanium. And Lowest background has been achieved by Ge detector.

8. Energy Threshold of Detector
less than 100eV after PSD
Manganese54, 22Ti (titanium)
PSD Parameter: for every current shape
100eV

9. The Aim of Our experiment
Our estimated results:
Target mass: 5g
Counts rate: count/keV·kg·day
Threshold: 100 eV
Upgrade to 1kg Ge

10. CsI Compton veto Detector

11. CsI Crystal Structure Top: Bottom: 150mm50mm
29 degree slope from height 30mm
76mm at top
Bottom:
150mm30mm

12. CsI Crystal Structure Wall (6 parts): R=75 mm; r=45 mm 5 L=220 mm;
Outlet hole
(see pic before)

13. Photon Collection PMT performance:
CR119, one, at the top of CsI crystal
low background, good stability
Minus HV: -1.5KV
Anode resistance : 10K
Current: < 1mA
Reflecting film covers all surface of crystal .

14. Shielding for high energy gamma.
Compton Veto Function
Shielding for high energy gamma.

15. Primary Performance Test
Place : Tsinghua, China
Time : 16-18,Aug,2004
Source : Cs-137, Co-60
Bias: 12V
HV: -1000V
Void inside

16. Co-60 test result
Resolution becomes better when the source moves form bottom to top.
Peak moves since amplifier threshold adjusted.

17. Cs-137 test result
The result seems bad while source near the bottom. That is because of the energy which is not high enough.

18. Comparison of two sources

19. Test Conclusion Photon collection efficiency Ray Energy
Efficiency becomes worse while source moving from top to bottom because only one PMT is used, at top.
Ray Energy
Higher energy ray can be detected more easily than lower one, which is good for high energy gamma ray shielding in this experiment.
, that is because the PMT is on the top. When photons are collected to the PMT, some of them are lost.

20. Plan Now: Nov: Dec: CsI detector was sent to Korea
Installation in Y2L and advanced test
MC simulation
Dec:
Built up with HPGe detector

21. Thank you!