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Status of ULE-HPGe Experiment for WIMP Search

Status of ULE-HPGe Experiment for WIMP Search. Li Xin (Tsinghua University) KIMS collaboration. Feb. 7th, 2006. 5g Ge. 1cpd. Motivation. Low mass Dark Matter candidate search Low energy threshold necessary Use 5g of prototype Ge detector ( plan to upgrade up to 1 kg ).

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Status of ULE-HPGe Experiment for WIMP Search

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  1. Status of ULE-HPGe Experiment for WIMP Search Li Xin (Tsinghua University) KIMS collaboration Feb. 7th, 2006

  2. 5g Ge 1cpd Motivation • Low mass Dark Matter candidate search • Low energy threshold necessary • Use 5g of prototype Ge detector ( plan to upgrade up to 1 kg ) Expected threshold: ~100eV

  3. Current System Setup ULE - HPGe detector FADC & VME crate H.V. (CEAN 1527) Amp. (CANBERRA 2026) HPGe: -500V CsI(Tl): -1300V Shaping time: 6us Gain: ×20

  4. DAQ System • DAQ device: 4-channel FADC SR=64MHz, 12bit 64 us window USB2.0 interface Typical signals: HPGe High gain (0~9keV) HPGe Low gain (0~100keV) CsI(Tl) channel (current signal)

  5. X-ray Generator LiTaO3 (From http://www.amptek.com )

  6. X-ray Generator (From http://www.amptek.com )

  7. Structure of the HPGe Detector The carbon window can stop the particle with the energy less than about 1.5keV.

  8. HPGe Calibration – high gain channel Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray After gain correction and pedestal shift correction

  9. HPGe Calibration – low gain channel Peaks: Np (L X-ray), Ag (K X-ray), Am (alpha decay gamma)

  10. CsI Calibration Gamma energy: Cd-109 (Ag X-ray): 22.577 keV Am-241: 59.5412 keV U-238 (Th-234): 92.6 keV Co-57: 123.66 keV

  11. PSD Parameters for CsI noise reduction T-bar of CsI (Tl) Detail Red: background files (Oct. 4th ~ Oct. 18th) Blue: calibration file (Co-57) Green: neutron file Threshold for CsI: ~10keV

  12. Neutron Recoil Data for HPGe Source: Cf-252 (outside Pb shielding) Time: Nov. 2nd, 14:00~19:00 Time coincidence relation (2D) Time coincidence relation (1D) Energy spectrum Detail

  13. Threshold for HPGe Threshold Pulse shape (270 ~ 290 eV) Energy spectrum of background pedestal shape fitting Hardware threshold: ~ 150 eV Electronic noise level: τ~ 13 eV Threshold for HPGe: 300eV

  14. Background Data Analysis High gain channel Low gain channel

  15. Background Data Analysis High gain channel Low gain channel

  16. Background after Neutron Run High gain channel Low gain channel 10keV peak

  17. Background with Strong γSource Outside Source: U-238, Th-232, Eu-152 (Outside Pb shielding) High gain channel Low gain channel

  18. Summary • The ULE-HPGe system has been set up and the data taking has been run for several months. • Background level: abut 40 count/kg/day/keV (not from external gamma) • Veto efficiency: about 60% • Software threshold: about 300 eV • Question: • (1). Is the background level acceptable? • (2). Is the energy threshold correct?

  19. In the future… • Parameter selection for electronic system • Pulse shape study in low-energy region, and more accurate calibration • Monte-Carlo simulation for external and internal neutron, and build neutron shielding if necessary • Internal background study for HPGe and CsI(Tl)

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