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

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• 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

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Gain vs. High Voltage Plot

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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

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• Mini-darkbox

Gamma Ray Spectroscopy

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• New PMT Required splitter

Gamma Ray Spectroscopy

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• Splitter design

Gamma Ray Spectroscopy

Splitter circuit designed by Teppei Katori, FNAL

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• Pre-constructed splitter

Gamma Ray Spectroscopy

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• 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

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• 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

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Acknowledgements

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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

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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?