Download - 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

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%


11 772772 479479 41.096941.0969 62.0466%62.0466%

High gain channel Low gain channel

Background Data Analysis

datedate Threshold Threshold (keV)(keV)






0.30.3 611611 368368 44.182644.1826 60.7232%60.7232%


11 587587 361361 45.033445.0334 61.4991%61.4991%


Background after Neutron Run






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%


10keV peak

Background with Strong γSource Outside







0.30.3 830830 516516 44.440244.4402 62.1687%62.1687%


11 791791 508508 39.744139.7441 64.2225%64.2225%


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)