Anti-Neutrino Simulations
And Elimination of Background Events
Kansas State REU ProgramAuthor: Jon Graves
Topics What are neutrinos? How do we measure them?
Double Chooz Fast neutrons Simulations and analysis Results Conclusion KamLAND Final Remarks
What Are Neutrinos? Nearly massless Three “flavors” Mass oscillations Sources
Fusion Fission CMBR Super Novae Cosmic Rays
What Are Neutrinos? Reactions
Neutron Transformation --->
Proton Transformation
Flavors Electron, Muon, Tau
Detection yields 1/3 the value expected
€
ν e+p→n+e+
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 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 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
Dominant Elements in Earth’s Crust
A report confirms these additions plus Cl.
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
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 100s” window.
Simulations and analysis
Simulated 500,000 events with correctly configured macro at two different rock thicknesses.
Results 400.0mm rock thickness
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 multi-
neutron events
Results
Results 4000.0mm rock thickness
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.