Transcript Slide 1
XENON Dark Matter Project
Karen Chen Boston College Nevis Labs, Columbia REU 2009 1
Outline
I: Xenon Detector Concepts ER and NR Discrimination II: Previous Work XENON100 III: Current Work XENON100 Upgrade 2
Xenon Detector Concept
anode
Xe Dual phase TPC Evidence of non-baryonic dark matter WIMPs Elastic collisions
cathode
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Xenon Detector Concept
anode cathode
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2.
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5.
Interaction (S1) Light e- drift Proportional scintillation (S2) Light 4
ER and NR Sources
Nuclear recoils (NR) Neutrons muons (alpha,n) WIMPs Electronic recoils (ER) construction materials 5
ER and NR Sources
Maximize WIMP events Large detector size Minimize Background Low radioactivity materials Shielding Underground laboratory (LNGS) 6
XENON Detectors
Past, Present, and Future
XENON10 (2005-2007) Demonstrated dual phase xenon TPC for WIMP search XENON100 (2006-2009) 50kg fiducial volume (FV) mass Simulation and Experimental results
XENON100+ (2009-2012)
100kg FV Under current R&D (that’s me!)
Detector Geometry Background simulations
Based on XENON100 data
XENON1T (2013-2015) 1 ton FV Early R&D 7
XENON100
Screen materials for radioactivity 238 U, 232 Th, 40 K, and 60 Co Ge detector Vary by manufacturer and thickness
Measured radiation rates for materials in XENON100 (plus QUPIDS)
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XENON100
How many bananas is that?
PMTs and bases – 4.2 Bq Stainless steel – 4.1 Bq PTFE – 0.1 Bq Total – 8.4 Bq Banana* ~ 20 Bq, ~2x Human** ~ 4000 Bq, ~476x **Wikipedia *http://www.radlab.nl/radsafe/archives/9503/msg00074.html
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XENON100
Background rate for different materials
MC Simulation by Alex
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PMTs and QUPIDs
Primary BG source
Photomultiplier tubes (PMTs) Lowest radioactivity on the market!
Need lower radioactivity PMTs!
Quartz Photon Intensifying Detector (QUPID) Developed by Hamamatsu Photonics and Prof. Arisaka (UCLA) 11
PMTs and QUPIDs
XENON10 and XENON100
98 top PMTs with ~24% QE 80 bottom PMTs with ~34% QE
XENON100+ and XENON1T
Same top array 19 bottom QUPIDs $$$ QUPIDs created for XENON100 Upgrade 12
XENON100 Upgrade
Improvements on XENON100 Reducing Background Lower radioactivity materials QUPIDs More Xe, less material Cryostat - Domed for stability Steel thickness from 1.5mm to 0.1mm
Need to test Exception: More can be better Shielding Scaling Up Add radius or height?
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XENON100 Upgrade
Steel vs Copper Cryostat
MC Simulation by Alex
Copper High thermal conductivity Soft Metal Low BG Stainless Steel Medium thermal conductivity Sturdy High BG 14
XENON100 Upgrade
LXe 170K Copper High thermal conductivity Soft Metal Low BG Stainless Steel Medium thermal conductivity Sturdy High BG 15
Shielding
Separate the xenon Cooling tower moved for Xenon100 The trade off: Less external BG neutrons, muons More intrinsic BG radioactive decay Cutting Costs: XENON1T Shield Shielding for Xenon100 Upgrade 16
XENON100 Upgrade
Detector Geometry Double the mass Height or radius?
Radius limited by QUPIDs Increase the height height drift length Drift Length Concerns High voltage Pileup Problem
QUPIDs
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Pileup Problem
What is pileup?
Events recorded by trigger Noise or signal?
Record length Time for electron to drift from one end to the other S1 and S2 signal in one event Multiple events -> Uncertainty 18
Pileup Problem
Detector 1.
2.
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Event A S1 Signal Electron A drifts Event B S1 Signal Electrons drift Event B S2 Signal Event A S2 Signal Which signal corresponds to which event?
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Pileup Problem
Estimate likelihood of pileup
n
= true interaction rate
m
= recorded count rate
τ
= dead time (record length)
m = ne -nτ* Percent Loss = 1 - e -nτ
But what is the trigger rate?
20 *Radiation Detection and Measurement by Knoll pgs 120-123
XENON100 Upgrade
Ideas into Monte Carlo Simulations If I use this geometry, what BG can I expect?
Geant4 Create the detector geometry XENON100 Simplified: Bell, Cryostat, PMTs, Teflon panel Simulate the decay chains 238 U, 232 Th, 40 K, 60 Co Scale by radioactivity of each material Analyze - Make appropriate cuts Multiple scatters, energy Fiducial volume 21
XENON100 Upgrade
Steel Cryostat (Inner) Bell PMTs Teflon Panel Steel Cryostat (Inner) Teflon QUPIDs TPC/Target Xe Veto
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XENON100 Upgrade
Ideas into Monte Carlo Simulations If I use this geometry, what BG can I expect?
Geant4 Create the detector geometry XENON100 Simplified: Bell, Cryostat, PMTs, Teflon panel Simulate the decay chains 238 U, 232 Th, 40 K, 60 Co Scale by radioactivity of each material Analyze - Make appropriate cuts Multiple scatters, energy Fiducial volume 23
XENON100 Upgrade
Simulation check: Rates scale with mass XENON100 (Alex) XENON100 Upgrade (Karen) 24
XENON100 Upgrade
Side note: Manipulating energy spectrum with thickness K40 U238 Th232 Co60 K40 U238 Th232 Co60 25
XENON100 Upgrade
Side note: Material thickness and K-40 spectrum 26
XENON100 Upgrade
Event Rate and Energy All Materials PMTs Steel Teflon Copper Trigger rate estimate: ~0.05Hz
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XENON100 Upgrade
Ideas into Monte Carlo Simulations If I use this geometry, what BG can I expect?
Geant4 Create the detector geometry XENON100 Simplified: Bell, Cryostat, PMTs, Teflon panel Simulate the decay chains 238 U, 232 Th, 40 K, 60 Co Scale by radioactivity of each material Analyze - Make appropriate cuts Multiple scatters, energy Fiducial volume 28
XENON100 Upgrade
Number of scatters Detector Resolution ~3mm Single scatter events in the target volume Good efficiency from PMTs Events in the xenon veto Low efficiency of veto PMTs need >50keVee of energy 29
XENON100 Upgrade
Different energy in veto cuts 30
XENON100 Upgrade
Different energy in veto cuts Histogram of events in the best volume cut 31
XENON100 Upgrade
Xenon100 Event distribution (Alex) Event Distribution Fiducial Volume Cut Low background core Radial vs Height cuts 32
XENON100 Upgrade
Event Distribution: PMTs 33
XENON100 Upgrade
Event Distribution: Steel 34
XENON100 Upgrade
Event Distribution: Teflon 35
XENON100 Upgrade
Event Distribution: Copper 36
XENON100 Upgrade
Event Distribution: All 37
XENON100 Upgrade
Event Distribution Patterns Top Heavy: Steel and PMTs Radial: Teflon, Steel (somewhat) Radial cut - - - - - - - - - - - - > Height cut 38
XENON100 Upgrade
Added Top Xenon Veto
Xe Top Veto Xe Veto
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XENON100 Upgrade
Current Design and BG rate Steel contribution is lowered!
Looks promising!
Reached low background rates in proposal Doubled FV 40
Summary
XENON100 BG contribution from different materials XENON100 upgrade Steel vs Copper cryostat Doubling the mass -> height ->drift length Pileup – not an issue Ideas for detector geometry Analyzed MC simulation results Effect of veto energy cut Background levels, trigger rate Re-simulated with top LXe veto -> Steel BG BG levels within design levels in NSF proposal 41
Acknowledgements
XENON Group Rafael Elena Aprile Guillame, Bin, Kyungeun (Elizabeth), Luke Emily Nevis REU Mike Shaevitz, John Parsons All my fellow REU students 42
Questions?
XENON100 BG contribution from different materials XENON100 upgrade Steel vs Copper cryostat Doubling the mass -> height ->drift length Pileup – not an issue Analyzed MC simulation results Effect of veto energy cut Background levels, trigger rate Re-simulated with top LXe veto BG levels within design levels in NSF proposal 43