Anti-Neutrino Simulations And Elimination of Background Events Kansas State REU Program Author: Jon Graves

Topics What are neutrinos? How do we measure them? Fast neutrons 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 Flavors Neutron Transformation ---> Proton Transformation Flavors Electron, Muon, Tau Detection yields 1/3 the value expected

What Are Neutrinos? Sources Stars Radioactive Decay Super Novae 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 Gamma-Catcher LS and Gd Used for capturing neutrons Gamma-Catcher LS only Used for detecting gammas from prompt and delayed events

Double Chooz Buffer Inner Veto 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 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 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 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.