kathleen chinetti sohaila mali calibrating equipment for the direct detection of dark matter using...
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Kathleen ChinettiSohai la Mali
Calibrating Equipment for the Direct
Detection of Dark Matter using
Noble Element . Scintillation
• Dark Matter Background WIMPS Noble element scintillation
• How do we directly detect dark matter? DarkSide SCENE
• How do we test equipment for DM detectors? PMTs
Purpose
1
• Most commonly accepted model of DM is WIMPs Difficult to detect – nuclear recoil• Liquid noble element detectors convert nuclear
recoil energy into both… Scintillation – particle collision releases light Ionization – particle collision releases charge
Dark Matter Detection
2
• Liquid argon scintillation detector Large mass (cost effective) High scintillation light yields Good background discrimination
DarkSide
Figure 1. Construction of the 4-m diameter LAr chamber, housed underground at Gran Sasso National Laboratory in Italy. Next to it is a schematic of the detector.
Figures from CERN Courier and Nature
3
• Calibration and testing for the DarkSide project SCintillation
Efficiency of Noble Elements
SCENE Detector
Figure 2. The proposed SCENE detector. DM interactions will occur in the area enclosed in the red box. Here, scintillation from the DM-liquid argon interaction will be collected by a photomultiplier tube.
Figure from Cary Kendziora, FNAL
4
SCENE Detector at PAB
5
• Used to record the scintillation of the LAr
OUR TASK: Characterize a specific PMT.
Photomultiplier Tube (PMT)
6
• For every photon, how many electrons will be detected?
• Ultimately investigating the relationship between high voltage and gain
• Experimental design:
Calculating the PMT’s Gain
7
To oscilliscope / digitizer
PMT Pulse
8
PMT Gain Histogram
9
count · samples
Number of Events
• Fit a Gaussian distribution to the data to find the count· sample value of the single photoelectron peak
• Use the following equations to convert this count· sample value to gain (in electrons per
photon):
PMT Gain Calculations
10
Gain vs. High Voltage Plot
11
Figure 3. Calculated gain per volts for an RCA 6342A photomultiplier tube. Data were collected using histograms similar to the one on slide 9.
0 200 400 600 800 1000 1200 14001.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
Voltage (V)
Gain
(ele
ctro
ns p
er p
hoto
n)
• Spectroscopy determines the energy of gamma rays (“electromagnetic” calibration – electron recoil)
• General experimental design:
Gamma Ray Spectroscopy
To high voltage
To measuring device
ScintillatorDetector (PMT)Radioactive
source
Radioactive sources used:Cobalt-60Caesium-137
12
• Mini-darkbox
Gamma Ray Spectroscopy
13
• New PMT Required splitter
Gamma Ray Spectroscopy
14
• Splitter design
Gamma Ray Spectroscopy
Splitter circuit designed by Teppei Katori, FNAL
15
• Pre-constructed splitter
Gamma Ray Spectroscopy
16
• Should see several peaks Backscatter peak Compton edge –
distribution caused by Compton scattering within the crystal
Photopeak – full energy peak
• The position of the photopeak can be used to determine the gain of the detector
Analyzing Gamma Ray Spectrum
Figure 4. Example gamma spectrum of cobalt-60 using a thallium-doped sodium iodide crystal as a scintillator. From right: photopeak, Compton edge, backscatter peak.
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Cobalt-60 Gamma Ray Spectrum
18
• Calculate gain of SCENE PMT• Gamma ray spectroscopy of
SCENE PMT (with LAr as a scintillator)
• Photons per KeV calibration• Nuclear recoil calibration Neutron beam at Notre Dame Discriminate b/n nuclear &
electron recoils using charge to light ratio & pulse shape
Moving Forward
19
Acknowledgements
20
From top left:Chris Stoughton, Kristy Lubinski,
George Dzuricsko, Fritz DeJongh,
…..Stephen Pordes, …Jonghee Yoo,
Tom Alexander, . Henning Back,
Ben Loer, .Charles Cao,Ron Davis,..Kelly Hardin,Billy Miner,
Cary Kendziora, Teppei Katori
Acknowledgements
21
From top left:Chris Stoughton, Kristy Lubinski,
George Dzuricsko, Fritz DeJongh,
…..Stephen Pordes, …Jonghee Yoo,
Tom Alexander, . Henning Back,
Ben Loer, .Charles Cao,Ron Davis,..Kelly Hardin,Billy Miner,
Cary Kendziora, Teppei Katori
ANY QUESTIONS?
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