Kathleen Chinetti Sohaila 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: OUR TASK: Characterize a specific PMT. Photomultiplier Tube (PMT) Figure 3. Construction of the 4-m diameter LAr chamber, housed underground at Gran Sasso National Laboratory in Italy Figure from CERN Courier 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

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: Gain vs. High Voltage Plot 11 To oscilliscope / digitizer Figure 3. Calculated gain per volts for an RCA 6342A photomultiplier tube. Data were collected using histograms similar to the one on slide 9.

Spectroscopy determines the energy of gamma rays (“electromagnetic” calibration – electron recoil) General experimental design: Gamma Ray Spectroscopy To high voltage To measuring device Scintillator Detector (PMT) Radioactive source Radioactive sources used: Cobalt-60 Caesium

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. 17

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