XENON Dark Matter Search Juliette Alimena Columbia University REU August 2 nd 2007
Evidence of Dark Matter Missing mass in Coma galaxy cluster (Fritz Zwicky) Flat rotation curves of spiral galaxies (Vera Rubin) CMB anisotropies Supernova data Weak gravitational lensing
XENON Experiment Direct dark matter detection, looking for WIMPs Cold Dark Matter Non-Baryonic Neutralino and SUSY Pulse tube cryocooler Re-condenser 15 kg LXe Vacuum Cryostat
XENON Experiment S2 S1
My Projects Refined Simulation with Activated Xenon Data for XENON10 Began Tests of Avalanche Photodiodes
Activated Xenon Calibration Filled detector with 450g GXe,, irradiated for 12 days with a neutron source (Cf- 252) Added to LXe in February 2007 to finalize calibration AXe creates uniform, isotropic emission of gamma- rays to calibrate detector. Xe-129 creates 164 kev photon. Xe-131 creates 236 kev photon.
1st Project and Motivations Compared the AXe S1 signal reaching each PMT to that of the Monte Carlo simulation by finding Χ 2 Did this for several different versions of simulation that have different parameters Allows us to better understand what happens in the XENON10 detector, and to improve the larger models to come
Light Collection Efficiency Amplitude of PMT Signal A i PMT # E Deposited E ( x, y, z) = η ( x, i W s E to Create Scintillation Photon Fraction of Scintillation Light y, Quantum Efficiency z) Q G i Gain i C Collection Efficiency i
Light Collection Efficiency (cont) A A i i ( x, y, z) (0,0,7.5) = η η i i ( x, y, z) (0,0,7.5) Point at Center of Detector
AXe Data S2tot vs. S1tot
AXe Data 164 kev Photon Cut
PMT Classes I H H I G F C C F G E D A B A D E B B E D A B A D E G F C C F G I H H I
X-Y Y Projection of 2D Profiles AXe Data - Rel S1 Signal vs. Source Position for PMT #61
1D Histograms of Projections 5 <dt< dt< < 15 15 <dt< dt< < 25 25 <dt< dt< < 35 35 <dt< dt< < 45 45 <dt< dt< < 55 55 <dt< dt< < 65 65 <dt< dt< < 75
Comparison of the 4 PMTs in Class A 5 <dt< dt< < 15 15 <dt< dt< < 25 25 <dt< dt< < 35 35 <dt< dt< < 45 45 <dt< dt< < 55 55 <dt< dt< < 65 65 <dt< dt< < 75
Comparison of AXe Data to Simulation 5 <dt< dt< < 15 15 <dt< dt< < 25 25 <dt< dt< < 35 35 <dt< dt< < 45 45 <dt< dt< < 55 55 <dt< dt< < 65 65 <dt< dt< < 75 5 <dt< dt< < 15 15 <dt< dt< < 25 25 <dt< dt< < 35 35 <dt< dt< < 45 45 <dt< dt< < 55 55 <dt< dt< < 65 65 <dt< dt< < 75
Simulation Parameters Parameter Teflon Reflectivity Experimental Value 0.95* Values Given in Versions of Simulation 0.95, 0.975, 1.0 Absorption Length Rayleigh Scattering >100 cm** 29-50 cm** [6,8,11-13] 13] 50, 100, 125, 150, 200, 300, 500 cm 30 cm Index of Refraction 1.6-1.7** 1.7** [6-8] 1.69 *Kaixuan Ni, XENON work **A Baldini,, et. al., Absorption of scintillation light in a 1001 liquid xenon gamma-ray detector and expected detector performance, Nucl.. Inst. Methods, A 545, 2005
Χ 2 Between Data and Simulation for Different Simulation Parameters Simulation # Teflon Reflectivity Absorption Length [cm] Rayleigh Scattering [cm] Index of Refraction Total Χ 2 1 0.95 100 30 1.69 166191 2 0.95 125 30 1.69 179452 3 0.95 150 30 1.69 196519 4 0.95 200 30 1.69 171445 5 0.95 300 30 1.69 210122 6 0.95 500 30 1.69 178909 7 0.95 50 30 1.69 164090 8 0.975 100 30 1.69 178439 9 0.975 125 30 1.69 178149 10 1.0 100 30 1.69 170085 11 1.0 125 30 1.69 176646 12 1.0 150 30 1.69 176799
Results Conclusion of 1 st Project Version of MC simulation that is most consistent with AXe Data has the parameters 0.95 Teflon reflectivity, 50 cm absorption length, 30 cm Rayleigh scattering, and 1.69 index of refraction. Possible future steps Could improve error by making each spatial cell be smaller, i.e. < 6.28 cm 3 Perform analysis again including the top array of PMTs,, the S2 signal, and 236 kev photon Continue to vary parameters of simulation, possibly add more parameters that influence photon detection
2nd Project and Motivations Tested prototype Hamamatsu APDs (Avalanche Photodiodes) Allows us to determine how effective these APDs would be in LXe and GXe detectors
Avalanche Photodiodes More Accelerated Electrons Accelerated Electron Electron-Ion Pair Created Incident Photon
Comparing Photodetectors PMTs Internal gain: 10 8 Larger area Much lower overall sensitivity Higher noise Bulkier Lower QE Measurable radioactivity contamination APDs Internal gain: 10 2-10 3 Smaller area Spectral response: 190-1100 nm (silicon) Low noise Compact and lightweight, long lifetime High QE, often > 80% Negligible radioactivity contamination 1 cm PMT x & 1 cm PMT x Base 3.5 cm 1.6 mm x 1.6 mm
Test Setup Preamplifier
Linearity of Preamp/Amp/MCA System Linearity of Final Voltage as a function of Input Voltage Final Voltage (V) 140 y = 0.3639x + 1.2455 120 R 2 = 0.9997 100 80 60 40 1000 20 0 800 0 50 100 150 200 250 300 350 600 Input Voltage (mv) Linearity of MCA Channel as a function of Final Voltage MCA Channel 400 200 Linearity of MCA Channel as a function of Input Voltage y = 2.6643x + 31.487 R 2 = 0.9966 MCA Channel 1000 800 600 400 200 y = 7.3246x + 22.171 R 2 = 0.9977 0 0 50 100 150 200 250 300 350 Input Voltage (mv) 0 0 20 40 60 80 100 120 140 Final Voltage (V)
APD Detection of LXe & GXe Scintillation Direct scintillation from alpha source (Am- 241) measured as function of applied bias voltage on APD Began to determine APD gain as a function of bias voltage Noise problems from preamp: yet to confirm unitary gain
Example Spectrum for Alpha Particles Detected by APD Bias Voltage = -260 V Alpha Particles Test Pulse
Conclusion of 2 nd Project Results Electronic system is linear Can discern alpha peaks in LXe Possible future steps Continue to improve noise discriminations until able to determine unitary gain Determine relationship between APD gain and voltage Determine quantum efficiency of APD
Thank you! Professor Elena Aprile and the entire XENON group for all their guidance and help especially the members present at this presentation