CsI Compton Veto Detector for A low Mass WIMP Experiment He Dao KPS@Jeju University 23 Oct 2004

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

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.

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

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

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

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.

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

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

CsI Compton veto Detector

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

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

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 .

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

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

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

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

Comparison of two sources

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.

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

Thank you!