Status of ULE-HPGe Experiment for WIMP Search

Li Xin (Tsinghua University)KIMS collaboration

Feb. 7th, 2006

Motivation

5g Ge

1cpd

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

Current System Setup

HPGe: -500VCsI(Tl): -1300V

H.V. (CEAN 1527) Amp. (CANBERRA 2026)

Shaping time: 6usGain: ×20

ULE - HPGe detector FADC & VME crate

DAQ System

► DAQ device:DAQ device:

4-channel FADC4-channel FADC

SR=64MHz, 12bitSR=64MHz, 12bit

64 us window64 us window

USB2.0 interfaceUSB2.0 interface

Typical signals:

HPGe High gain(0~9keV)

HPGe Low gain(0~100keV)

CsI(Tl) channel(current signal)

X-ray Generator

(From http://www.amptek.com )

LiTaO3

(From http://www.amptek.com )

X-ray Generator

Structure of the HPGe Detector

The carbon window can stop the particle with the energy less than about 1.5keV.

HPGe Calibration – high gain channel

Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray

After gain correction and pedestal shift correction

2

113.13

12.9617

offset eV

ndf

HPGe Calibration – low gain channel

Peaks:

Np (L X-ray), Ag (K X-ray), Am (alpha decay gamma)

2

0.0694

20.67

offset keV

ndf

CsI Calibration

2

2.487

10.4607

offset keV

ndf

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

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

Neutron Recoil Data for HPGe

Energy spectrum

Source: Cf-252 (outside Pb shielding)Time: Nov. 2nd, 14:00~19:00

Time coincidence relation (1D)

Detail

Time coincidence relation (2D)

Threshold for HPGeThreshold Pulse shape (270 ~ 290 eV)

Hardware threshold: ~ 150 eVElectronic noise level: τ~ 13 eV

Threshold for HPGe: 300eV

Energy spectrum of background pedestal shape fitting

50ln(1/ ) 13 ln(10 ) 150( )E h eV

exp( )E

h

Background Data Analysis

datedate ThresholThreshold (keV)d (keV)

Total Total countscounts

Vetoed Vetoed countscounts

Background Background level (cpd)level (cpd)

Veto Veto efficiencyefficiency

Oct. 4th ~ Oct. 4th ~ 18th18th

0.30.3 802802 487487 44.182644.1826 60.7232%60.7232%

Oct. 4th ~ Oct. 4th ~ 18th18th

11 772772 479479 41.096941.0969 62.0466%62.0466%

High gain channel Low gain channel

Background Data Analysis

datedate Threshold Threshold (keV)(keV)

Total Total countscounts

Vetoed Vetoed countscounts

Background Background level (cpd)level (cpd)

Veto Veto efficiencyefficiency

Oct. 18th ~ Oct. 18th ~ 31th31th

0.30.3 611611 368368 44.182644.1826 60.7232%60.7232%

Oct. 18th ~ Oct. 18th ~ 31th31th

11 587587 361361 45.033445.0334 61.4991%61.4991%

High gain channel Low gain channel

Background after Neutron Run

datedate Threshold Threshold (keV)(keV)

Total Total countscounts

Vetoed Vetoed countscounts

Background Background level (cpd)level (cpd)

Veto Veto efficiencyefficiency

Nov. 3rd ~ Nov. 3rd ~ 11th11th

0.30.3 504504 294294 47.151847.1518 58.3333%58.3333%

Nov. 3th ~ Nov. 3th ~ 11th11th

11 465465 286286 40.191340.1913 61.5054%61.5054%

High gain channel Low gain channel

10keV peak

Background with Strong γSource Outside

datedate Threshold Threshold (keV)(keV)

Total Total countscounts

Vetoed Vetoed countscounts

Background Background level (cpd)level (cpd)

Veto Veto efficiencyefficiency

Nov. 11th ~ Nov. 11th ~ 25th25th

0.30.3 830830 516516 44.440244.4402 62.1687%62.1687%

Nov. 11th ~ Nov. 11th ~ 25th25th

11 791791 508508 39.744139.7441 64.2225%64.2225%

High gain channel Low gain channel

Source: U-238, Th-232, Eu-152 (Outside Pb shielding)

Summary

1. The ULE-HPGe system has been set up and

the data taking has been run for several

months.

2. Background level: abut 40

count/kg/day/keV (not from external

gamma)

3. Veto efficiency: about 60%

4. Software threshold: about 300 eV5. Question:

(1). Is the background level acceptable?

(2). Is the energy threshold correct?

In the future…

1. Parameter selection for electronic system

2. Pulse shape study in low-energy region, and more

accurate calibration

3. Monte-Carlo simulation for external and internal

neutron, and build neutron shielding if necessary

4. Internal background study for HPGe and CsI(Tl)