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.