Transcript Document

Anti-Neutrino Simulations
And Elimination of Background Events
Kansas State REU Program
Author: Jon Graves
Topics
 What are neutrinos?
 How do we measure them?
 Double Chooz
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Fast neutrons
Simulations and analysis
Results
Conclusion
KamLAND
Final Remarks
What Are Neutrinos?
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Nearly massless
Three “flavors”
Mass oscillations
Sources
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Fusion
Fission
CMBR
Super Novae
Cosmic Rays
What Are Neutrinos?
 Reactions
 Neutron
Transformation --->
 Proton
Transformation
 e  p  n  e 
 Flavors
 Electron, Muon, Tau
 Detection yields 1/3
the value expected
What Are Neutrinos?
 Sources
 Stars
 Radioactive Decay
 Nuclear Reactors
 Super Novae
View of the sun as seen in neutrinos. (Credit:
Institute for Cosmic Ray Research, Tokyo)
Supernova 1987A
How do we measure them?
 Anti-Neutrino -> Proton interaction
 Prompt signal
 Positron/Electron annihilation
----->
 Delayed signal
 Thermal neutron capture
 Gadolinium
 Hydrogen
Double Chooz
 In northern France
 Cylindrical
geometry
 Four volumes of
interest
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Target
Gamma-Catcher
Buffer
Inner Veto
Double Chooz
 Target
 LS and Gd
 Used for capturing
neutrons
 Gamma-Catcher
 LS only
 Used for detecting
gammas from
prompt and delayed
events
Double Chooz
 Buffer
 Mineral oil, a.k.a.
Buffer oil
 Shields inner active
volumes from
accidental backgrounds
 U & Th decay in PMTs
 PMTs line this volume
 Inner Veto
 Steel shield tags muons
Fast neutrons
 My goals
 How does the detector geometry affect the neutrons?
 How does the surrounding rock affect the neutrons?
 How often do the neutrons correlate to neutrino
events?
Simulations and analysis
 Macro parameters
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Rock shell thickness
Initial position of generated neutrons
Fill of generated neutrons
Number of events to simulate
 Geology
Geology
 Rocks surrounding detector are simulated using
the following elements:
 Gd, Ti, Ni, Cr, Fe, K, N, Al, Si, C, O
 The following elements are quite common in
northern France:
 Mn, Na, Ca, H, P, Mg
 A report confirms
these additions plus
Cl.
Dominant Elements in
Earth’s Crust
Simulations and analysis
 My energy deposition program
 Plot histograms of:
 Energy depositions within the detector
 Prompt/Delayed energies
 Time interval for prompt/delayed energies
 1 to 100 microseconds
 Initial/Final positions of neutrons
 Provide data analysis output in an organized
text format
Results
 10,000 events simulated, 4000.0mm rock thickness
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Target = 2
<------70.7% relative statistical error
Gamma-Catcher = 6
Buffer = 17
Inner Veto = 74
 Most neutrons are absorbed by the steel shield and
rocks
 No correlated events
 Should run 1,000,000 events for better error
analysis
PROBLEM!!
Problem
 After running 1,000,000 events, discovered no
correlations again.
 Further analysis revealed an improperly
configured option in the macro for the simulator.
 Simulator was set to merge events shorter than
1ms. This guarantees no correlations in the “1 to
100s” window.
Simulations and analysis
 Simulated 500,000 events with correctly
configured macro at two different rock
thicknesses.
Results
 400.0mm rock thickness
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Target = 108
<------9.6% relative statistical error
Gamma-Catcher = 306
Buffer = 1445
Inner Veto = 6196
 5.14% of deposition events occurred within the
target and gamma-catcher volumes.
 9 correlation events
 Eliminated all but 2 in final analysis due to multineutron events
Results
Results
 4000.0mm rock thickness
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Target = 32
<------17.7% relative statistical error
Gamma-Catcher = 63
Buffer = 271
Inner Veto = 1287
 5.75% of deposition events occurred within the target and
gamma-catcher volumes, similar to other thickness
 2 correlation events
 Eliminated both in final analysis due to multi-neutron events
 79.48% less events with a rock thickness 10 times greater.
Results
Conclusion
 Detector geometry (steel shield) and
surrounding rocks are effective in blocking
most high-energy neutrons.
 Neutron events rarely correlate to neutrino
events. However, this must still be
accounted for, considering neutrino events
themselves are rare.
 Two to three per day, on average
KamLAND
 Kamioka Liquid-scintillator
Anti-Neutrino Detector
 Kamioka Mine in
northwestern Japan (main
island)
 Spherical geometry
 Duties involve monitoring
equipment and ensuring
everything is operating at peak
efficiency.
 Hourly check
Final Remarks
 Learned a great deal about
programming, neutrinos,
detectors, real-world
experience.
 I made the right choice in
choosing a career path
involving high-energy
physics.