Electron Neutrino Appearance in the NOνA Experiment Ji Liu Hainan, China Master of Science ...

218 Pages·2016·22.93 MB·English

FERMILAB-THESIS-2017-01
Electron Neutrino Appearance in the NOνA Experiment
Ji Liu
Hainan, China
Master of Science, College of William and Mary, 2010
Bachelor of Physics, University of Science and Technology of China, 2009
A Dissertation presented to the Graduate Faculty
of the College of William and Mary in Candidacy for the Degree of
Doctor of Philosophy
Department of Physics
The College of William and Mary
January 2017
Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy
(cid:13)c 2017
Ji Liu
All rights reserved.
APPROVAL PAGE
This Dissertation is submitted in partial fulfillment of
the requirements for the degree of
Doctor of Philosophy
Ji Liu
Approved by the Committee, November, 2016
Committee Chair
Associate Professor Patricia Vahle, Physics
The College of William and Mary
Professor Jeff Nelson, Physics
The College of William and Mary
Professor Todd Averett, Physics
The College of William and Mary
Assistant Professor Justin Stevens, Physics
The College of William and Mary
Associate Professor Robert Craig Group, Physics
University of Virginia
ABSTRACT
The NuMI Off-Axis ν Appearance (NOνA) experiment is a long baseline, off-axis
e
neutrino oscillation experiment. It is designed to search for oscillations of ν to ν by
µ e
comparing measurements of the NuMI beam composition in two detectors. These two
detectors are functionally identical, nearly fully-active liquid-scintillator tracking
calorimeters and located at two points along the beam line to observe the neutrinos. The
Near Detector (ND), situated 1km away from the proton target at Fermilab, measures
neutrinos prior to oscillation. Then the Far Detector (FD), located 810 km away at Ash
River, Minnesota, measures the neutrinos after they have traveled and potentially
oscillated. The neutrino beam is generated at Fermi National Accelerator Laboratory in
Batavia, Illinois by the Neutrinos at the Main Injector (NuMI) facility.
By observing the ν → ν oscillation, NOνA is capable of measuring the neutrino mass
µ e
hierarchy, CP violation and the octant of mixing angle θ . This thesis presents the first
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measurement of ν appearance in the NOνA detectors with 3.52×1020 protons-on-target
e
(POT) data accumulated from February 2014 till May 2015. In this analysis the primary
ν CC particle selection LID observes 6 ν like events in the far detector with a
e e
background prediction of 0.99±0.11 (syst.), which corresponds to a 3.3σ excess over the
no-oscillation hypothesis. This results disfavors 0.1π < δ < 0.5π in the inverted mass
cp
hierarchy at 90% C.L with the reactor constrain on θ .
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TABLE OF CONTENTS
Acknowledgments vi
Dedication vii
List of Tables viii
List of Figures xi
CHAPTER
1 The Physics of Neutrinos 1
1.1 A Brief Experimental History of Neutrinos 1
1.1.1 Discovery of Neutrinos 1
1.1.2 Neutrino Oscillation 4
1.2 Neutrinos in the Standard Model 7
1.2.1 Basic Ingredients of the Standard Model 7
1.2.2 Weak Force and Interactions 11
1.2.3 Neutrino Mass in the Standard Model 14
1.3 Neutrino Oscillations 16
1.3.1 Three-Flavor Neutrino Oscillations 19
1.3.2 Two-Flavor Neutrino Oscillations 23
1.3.3 Neutrino Oscillations in Matter 24
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1.4 Neutrino Oscillations Experiments 27
1.4.1 Reactor Antineutrino Experiments 27
1.4.2 Accelerator Neutrino Experiments 29
1.5 Summary and Current Status 30
2 The NOνA Experiment 32
2.1 NOνA Overview and Physics goals 32
2.2 The NuMI Beamline 34
2.2.1 Basic Principle 35
2.2.2 The Target 36
2.2.3 Electromagnetic Focusing Horns 39
2.2.4 Decay Volume and Absorber 40
2.2.5 NuMI Upgrade 41
2.3 Off-Axis Features 42
3 The NOνA Detector 45
3.1 The NOνA Detector Design 45
3.1.1 The Basic NOνA Detector Element 47
3.1.2 Liquid Scintillator 48
3.1.3 Wavelength-Shifting Fiber 49
3.1.4 Photodetector and Electronics 49
3.1.5 PVC Modules 54
3.2 Assembly of NOνA Detectors 57
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4 Monte Carlo Simulation 63
4.1 NOνA Simulation Chain 63
4.2 Neutrino Interaction Physics Models in GENIE 65
4.2.1 Cross Section Model 66
4.2.2 Neutrino-induced Hadron Production 68
4.2.3 Intranuclear Hadron Transport 68
4.2.4 Nuclear Physics Model 70
5 Calibration and Event Reconstruction 71
5.1 Calibration 71
5.1.1 Attenuation Calibration 73
5.1.2 Absolute Energy Calibration 75
5.1.3 Timing Calibration 77
5.2 Reconstruction 77
5.2.1 Slicer4D 78
5.2.2 Hough Transform 81
5.2.3 Elastic Arm Vertex Finding 84
5.2.4 Fuzzy K-Means Algorithm 86
6 ν Event Selection 89
e
6.1 NOνA Event Topologies 90
6.2 Data Quality Selection 90
6.2.1 Beam Quality 91
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6.2.2 Subrun Data Quality 92
6.3 ν Event Selection 94
e
6.3.1 Reconstruction Quality Cuts 95
6.3.2 Containment Cuts 96
6.3.3 Cosmic Ray Rejection for Far Detector 99
6.3.4 Preselection Cuts 100
6.4 ν Particle Identification 102
e
7 ν Appearance Analysis 106
e
7.1 First Measurement Data 106
7.2 Data vs. MC Comparisons 108
7.2.1 ND Data vs. MC Comparison 109
7.2.2 FD Data vs. MC Comparison 114
7.3 Decomposition 117
7.4 Extrapolation 118
7.5 Far Detector Background and Signal Prediction 122
8 Systematics 126
8.1 Beam Systematic Uncertainties 127
8.2 Scintillator Saturartion Systematic Uncertainties 130
8.3 Calibration Systematic Uncertainties 131
8.4 Light Level Systematic Uncertainties 135
8.5 Neutrino Interaction Systematic Uncertainties 137
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8.6 Containment 152
8.7 Rock Contamination 153
8.8 Decomposition 154
8.9 Alignment 155
8.10 Data and Monte Carlo Statistics 156
8.11 Normalization 157
8.12 Summary 157
9 Results 159
9.1 Sideband Study 159
9.2 NOνA ν Appearance Result 160
e
9.2.1 ν Appearance Candidates 161
e
9.2.2 Confidence Interval 171
9.3 Conclusion 178
BIBLIOGRAPHY 179
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ACKNOWLEDGMENTS
First and foremost I want to thank my advisor Patricia Vahle. For your guidance and
mentorship through the whole journey of my Ph.D. For your enthusiasm and knowledge
to neutrino physics that benefited a lot to both my study and this thesis. For your
patient and support during the past 7 years when I tried to balance my research and
personal life. I’m truly grateful to have you as my Ph.D advisor.
I want to thank Professor Jeff Nelson, who introduced me to the Neutrino group of
William and Mary and has been one of my committee for every annual review. Thank
you for all your suggestions and ideas through all these years.
I want to thank the other members of my graduate committee: Todd Averett, Robert
Craig Group and Justin Stevens, for your time and effort to review my thesis and give
valuable suggestions.
I want to thank all the members in the NOνA collaboration, who has been doing an
excellent job in putting together the detectors and collecting data. Especially I want to
thank the ν appearance analysis group, this thesis would not be possible without the
e
contribution from each group member. The group conveners Patricia Vahle and Mayly
Sanchez, thank you for your guidance and valuable suggestions. All the members in the
ν group, including but not limit to: Alex Radovic, Chris Backhouse, Evan Niner, Tian
e
Xin, Kanika Sachdev, Hongyue Duyang, Jianming Bian, Erika Catano-Mur, and Xuebing
Bu, thank you for all the discussion and help during this analysis.
I also would like to thank all the members in the Neutrino group of William and Mary:
Patricia Vahle, Jeff Nelson, Mike Kordosky, Alex Radovic, Alena Devan, Anne Norrick,
Marco Colo, Dun Zhang and Leonidas Aliaga-Soplin. Thank you for all the good time
that we work and travel together.
Above all, I would like to extend a heartfelt thanks to my family. Thank you, mom and
dad, for raising me up with all your love and supporting all my decisions. Lastly, thank
you, my dearest husband Siyuan, for your love and encouragement, for always being
there for me every step through this journey.
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