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Improving Energy Estimation at Nova with Recurrent Neural Networks Improving Energy Estimation at NOvA with Recurrent Neural Networks A DISSERTATION SUBMITTED TO THE FACULTY OF THE UNIVERSITY OF MINNESOTA BY Dmitrii Torbunov IN PARTIAL FULFILLMENT OF THE REQUIERMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Gregory Pawloski May, 2021 © Dmitrii Torbunov 2021 ALL RIGHTS RESERVED Contents Contents i List of Tables v List of Figures vi 1 Introduction 1 2 Neutrino Oscillations 4 2.1 Physics of Neutrino Oscillations ..................... 4 2.1.1 Formalism ............................. 6 2.1.2 Two Flavor Neutrino Oscillation Case ............. 8 2.1.3 Three Flavor Case ........................ 10 2.1.4 Three Flavor Neutrino Oscillations for Small L=E ....... 12 2.1.5 Three Flavor Neutrino Oscillations for Large L=E ....... 12 2.1.6 Neutrino Oscillations in Matter ................. 13 2.2 Neutrino Oscillation Experiments .................... 15 2.2.1 Discovery of the Neutrino Oscillations ............. 16 2.2.2 Verification of the Neutrino Oscillation Model ......... 20 2.2.3 Next Generation Neutrino Experiments ............ 22 3 The NOvA Experiment 24 3.1 Physical Goals of the NOvA Experiment ................ 25 3.2 Design of the NOvA Experiment .................... 26 3.2.1 The NuMI Beam ......................... 26 i 3.2.2 NOvA Detectors ......................... 28 3.2.3 The NOvA Far Detector ..................... 33 3.2.4 The NOvA Near Detector .................... 33 3.3 NOvA Data Acquisition System (DAQ) ................. 35 3.3.1 NOvA Event Displays ...................... 36 3.4 Sensitivity of the NOvA Experiment .................. 36 4 Detector Calibration and Event Simulation 40 4.1 Calibration ................................ 41 4.1.1 Energy Calibration ........................ 41 4.1.2 Timing Calibration ........................ 45 4.2 Simulation ................................. 47 4.2.1 Beam Simulation ......................... 49 4.2.2 Simulation of Neutrino Interactions ............... 49 4.2.3 Simulation of Propagation of Daughter Particles ........ 50 4.2.4 Simulation of the Detector Response .............. 50 5 Event Reconstruction 54 5.1 Hit Clustering ............................... 55 5.1.1 Slicing ............................... 55 5.1.2 Identification of Linear Features ................. 56 5.1.3 Identification of the Interaction Vertex ............. 57 5.1.4 Finding Clusters of Hits Describing Individual Particles .... 58 5.1.5 Clustering Summary ....................... 59 5.2 Tracking Particles ............................. 60 5.2.1 Muon Tracking with Kalman Filter ............... 60 5.2.2 Particle Tracking with Break Point Fitter ........... 62 5.3 Particle Identification ........................... 63 5.3.1 Muon Identification with RemID ................ 64 5.3.2 Electron Shower Identification with ShowerLID ........ 65 5.3.3 Multiclass Particle Identification with Prong CVN ...... 66 5.4 Event Identification ............................ 66 5.4.1 NuMu CC Events Identification with RemID ......... 68 ii 5.4.2 NuE CC Events Identification with ShowerLID ........ 69 5.4.3 Multiclass Event Identification with Event CVN ........ 70 5.4.4 Cosmic Rays Rejection ...................... 70 5.5 Energy Reconstruction .......................... 71 5.5.1 NuMu Energy Reconstruction .................. 71 5.5.2 NuE Energy Reconstruction ................... 74 5.5.3 Performance of Energy Estimators ............... 75 6 Analysis 78 6.1 Sample Selection ............................. 79 6.1.1 NuMu CC Sample Selection ................... 81 6.1.2 NuE CC Sample Selection .................... 81 6.2 Binning Selection ............................. 82 6.2.1 NuMu CC Sample Binning ................... 82 6.2.2 NuE CC Sample Binning .................... 85 6.3 Decomposition .............................. 85 6.3.1 NuMu CC Sample Decomposition ................ 86 6.3.2 NuE CC Sample Decomposition ................. 87 6.4 Extrapolation ............................... 88 6.4.1 Full Extrapolation ........................ 89 6.4.2 Partial Extrapolation of Backgrounds .............. 90 6.5 Estimation of the Oscillation Parameters ................ 91 6.6 Systematic Uncertainties ......................... 92 6.6.1 Construction of Predicted Neutrino Spectra as a Function of Systematic Shifts ........................ 95 6.7 Concluding Remarks ........................... 95 7 Improving Analysis with Recurrent Neural Networks 97 7.1 Recurrent Neural Networks ....................... 97 7.1.1 Brief History of Artificial Neural Networks ........... 97 7.1.2 Recurrent Neural Networks ................... 100 7.2 LSTM Energy Estimator ......................... 101 7.2.1 Energy Estimation for the NuMu Disappearance Analysis .. 101 iii 7.2.2 The LSTM Energy Estimator Concept ............. 103 7.2.3 LSTM EE Development: Network Architecture and Input Variables ............................. 104 7.2.4 LSTM EE Development: Sample Selection ........... 109 7.2.5 LSTM EE Development: Low Energy Bias Correction .... 113 7.2.6 LSTM EE Development: Weights Tuning for the Near Detector117 7.2.7 LSTM EE Development: Sensitivity to the Major NOvA Sys- tematics .............................. 121 7.2.8 LSTM EE Development: Reduction of the Sensitivity to the Calibration Systematic ..................... 128 7.2.9 LSTM EE Development: Final Words ............. 131 7.3 SliceLID Event Classifier ......................... 132 7.3.1 SliceLID Development: Initial Studies ............. 133 7.3.2 SliceLID Development: Making Multitarget Classifier ..... 135 7.3.3 SliceLID Development: Classifying ντ -CC events ....... 137 7.3.4 SliceLID Development: Classifying Cosmic Events ....... 140 7.3.5 SliceLID Development: Network Architecture Tuning ..... 141 7.3.6 SliceLID Performance ...................... 143 7.3.7 SliceLID Conclusion ....................... 145 8 Results 146 8.1 LSTM Energy Estimator ......................... 146 8.2 SliceLID .................................. 150 9 Conclusions 153 Glossary 155 Bibliography 157 A LSTM EE Results on Real Data 164 A.1 Data/MC Comparison at the Near Detector .............. 164 A.2 Data Contours .............................. 165 iv List of Tables 7.1 Summary of the inputs that the original Proof of Concept LSTM en- ergy estimator was using. The left column shows prong level variables and the right column shows the slice level variables. ......... 105 7.2 Summary of the refined inputs of the LSTM energy estimator. .... 108 7.3 Summary of the inputs of the SliceLID classifier. ............ 135 v List of Figures 2.1 Neutral and Charged Current neutrino interaction vertices according to the Standard Model. lα are the charged leptons (α 2 fe; µ, τg) and να are the corresponding neutrinos. .................. 5 2.2 Possible elastic interactions of the νe and νµ with the ordinary matter. f denotes a fermion (p, n, e). ...................... 14 3.1 Locations of the NOvA Near and Far Detectors. Source [12]. .... 25 3.2 Schematic representation of the NuMI Beamline. Source [13]. .... 27 3.3 Simulated NuMI energy spectrum for different off-axis detector align- ments. The NOvA detectors sit at around 14 mrad (red distribution). Source [13]. ................................ 29 3.4 Schematic representation of the NOvA detectors. ........... 30 3.5 Schematic representation of the NOvA detector cell. Source [12]. .. 31 3.6 Schematic representation of the NOvA extrusion module. Source [12]. 32 3.7 Photo of the Far Detector. The Far Detector side facing the reader is supported by a movable block pivoter (red). .............. 34 3.8 Plan view (bottom) and elevation view (top) of the NuMI beamline and the NOvA Near Detector. Source [12]. .............. 35 3.9 Example of the Far Detector NOvA Event Display. The hits are colored by the amount of charge deposited. .............. 37 vi 3.10 Example of a bi-probability plot for the NOvA experiment. The hori- zontal and vertical axes show the probability of neutrino and antineu- trino oscillations. The contours represent possible values of measure- ments of these oscillation probabilities, depending on the octant of θ23 2 (UO – upper octant, LO – lower octant), sign of ∆m32 (NH – normal hierarchy m3 > m2, IH – inverted hierarchy m3 < m2), and the CP violation phase δCP. The δCP changes continuously in each contour from 0 to 2π. ............................... 38 4.1 Example of an attenuation profile for a single vertical cell at theNear Detector. The red curve shows the double exponential fit (4.1). The blue curve shows the double exponential fit with the edge correction. 44 4.2 Comparison of the simulated muon energy deposition calculated using the Bethe-Bloch equation (left) to the measured muon energy deposi- tion expressed in terms of the detector response PECorr/cm (right). ....................................... 45 4.3 Example of the Far Detector timing resolution histogram for a single DCM. ................................... 48 4.4 Two-dimensional histogram of the light tracing simulation. The hori- zontal axis shows the distance along the direction of the cell between a point where the light was emitted and a point where the light entered the wavelength shifting fiber. The vertical axis shows the difference between the emission time and the collection time. .......... 52 4.5 Example of a light attenuation curve used to propagate photons through the fiber. The red curve is the old curve that was used in theFirst NOvA Analysis. The blue curve is the revised curve. ......... 53 5.1 Examples of neutrino interaction event topologies observed in the NOvA detectors. The
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