University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 12-2006 Combined Study of Reactor and Terrestrial Antineutrinos with KamLAND Mikhail Batygov University of Tennessee - Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Physics Commons Recommended Citation Batygov, Mikhail, "Combined Study of Reactor and Terrestrial Antineutrinos with KamLAND. " PhD diss., University of Tennessee, 2006. https://trace.tennessee.edu/utk_graddiss/1918 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Mikhail Batygov entitled "Combined Study of Reactor and Terrestrial Antineutrinos with KamLAND." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Physics. Yuri Kamyshkov, Major Professor We have read this dissertation and recommend its acceptance: William Bugg, Robert Compton, George Siopsis Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I am submitting herewith a dissertation written by Mikhail Batygov entitled “Com- bined Study of Reactor and Terrestrial Antineutrinos with KamLAND”. I have exam- ined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Physics. Yuri Kamyshkov Major Professor We have read this dissertation and recommend its acceptance: William Bugg Robert Compton George Siopsis Accepted for the Council: Linda Painter Interim Dean of Graduate Studies (Original signatures are on file with official student records) Combined Study of Reactor and Terrestrial Antineutrinos with KamLAND A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Mikhail Batygov December 2006 Copyright c 2006 by Mikhail Batygov All rights reserved. ii Dedication This dissertation is dedicated to my mother, Iraida Petrovna Vishnevskaya, and my father, Sergey Khachaturovih Batygov, who have always supported and encouraged me to stand up to the challenges of life. iii Acknowledgements This study is the result of the efforts of the whole KamLAND collaboration. I would like to thank every KamLAND collaborator for the contribution to the operation of the experiment which made the work presented here possible. KamLAND is supported by the Center of Excellence program of the Japanese Min- istry of Education, Culture, Sports, Science and Technology under grant 09CE2003, and by the United States Department of Energy under grant DE-FG02-91ER40627. The reactor data is provided courtesy of the following electric associations in Japan: Hokkaido, Tohoku, Tokyo, Hokuriku, Chubu, Kansai, Chugoku, Shikoku, and Kyushu Electric Power Companies, Japan Atomic Power Company, and the Japan Nuclear Cycle Development Institute. The Kamioka Mining and Smelting Company has pro- vided service for the activities in the mine. KamLAND was made possible by the scientific vision of Atsuto Suzuki whose ideas have led to the astounding success of KamLAND experiment. Of all KamLAND collaborators I feel most indebted to my advisor Yuri Kamyshkov for his support and for his patience. His remarkable expertise in nearly all aspects of modern particle physics has been an essential resource without which this work could have never been done. Other University of Tennessee KamLAND group members helped me a lot as well. William Bugg and Yuri Efremenko shared their vast experi- ence with me and helped to avoid many mistakes. I would like to thank Alexandre Kozlov for the simulation of energy deposition in scintillator and Oleg Perevozchikov for reactor data file format conversion which saved me a lot of efforts during the work on this thesis. A significant part of my work in KamLAND has been done at RCNS of the To- hoku University in Sendai or in a close interaction with this institution. It was a real pleasure to work at RCNS and I would like to thank all people whom I dealt there with. Of crucial importance was the notably efficient organization of KamLAND data analysis by Kunio Inoue. The explanations of analysis techniques that I got from him were among the main factors that predetermined this study. I also feel very grateful to Sanshiro Enomoto for his explanations of the key methods for terrestrial antineu- trino study, to Itaru Shimizu and Koichi Ichimura for their indispensable help with RCNS software and reactor data analysis methodology, to Yoshihito Gando and Kyo iv Nakajima for the preparation of reactor data, to Tadao Mitsui and Yasuhiro Kishi- moto for fruitful discussions and to Kyohei Nakajima for both interesting discussions and for his friendly help with everyday problems. The help from the American part of KamLAND collaboration was essential as well, especially during the latest stage of my thesis work. The discussions with Glenn Horton-Smith, Patrick Decowski, Brian Fujikawa, Dan Dwyer and Kazumi Tolich helped me with data analysis and simulation software and clarified some complicated issues associated with the analysis itself. I feel very grateful to John Learned for his encouragement to carry out the directionality study. That study provided insights which later proved absolutely necessary for the main topic of this thesis. I would like to thank all people who helped me during my stays in Mozumi, regard- less whether this help was about technical aspects of KamLAND operation, solving everyday problems or just moral support. Of former and present KamLAND mem- bers, I feel most obliged to Evgueni Yakushev, Jason Detwiler, Mitsuko Murakami, Charles Lane, Masayuki Koga, Kengo Nakamura for the support I got from them in Mozumi. Last but not least I would like to express my deepest gratitude to Katsuko Shimizu for her kindness, hospitality and friendship. v Abstract This dissertation presents a combined study of antineutrinos of terrestrial and reactor origin detected by Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND). Of special physical interest are neutrino oscillation parameters and the terrestrial antineutrino flux, the former being of a profound importance for new physics beyond the Standard Model, and the latter having significant implications for geophysics. The analysis described here uses a comprehensive likelihood model to naturally combine terrestrial and reactor antineutrino studies within a single framework. The use of this likelihood model and better event reconstruction tools allowed to obtain narrower limits for the oscillation parameters and the terrestrial antineutrino fluxes than separate reactor and terrestrial antineutrino KamLAND studies had provided before. 2 2 Based on 944.4 days of exposure, neutrino oscillation parameters ∆m12, sin 2θ12 +0.19 −5 2 +0.084 are obtained to be 7.52−0.18 10 eV and 0.916−0.134, respectively, at 0.68 confidence level (CL). × +19.9 The terrestrial antineutrino rate at KamLAND site is determined to be 46.6−19.2 TNU (Terrestrial Neutrino Units, i.e. events per 1032 protons per year) at 0.68 CL. vi Contents 1 Introduction 1 1.1 Neutrinos: Prediction and Observation . ... 1 1.2 NeutrinoOscillations ........................... 2 1.3 MSWmattereffect ............................ 6 1.4 SolarNeutrinoProblem ......................... 7 1.5 AtmosphericNeutrinos . .. .. 10 1.6 AcceleratorNeutrinos. .. .. 12 1.7 ReactorAntineutrinos .......................... 13 1.8 TerrestrialAntineutrinos . 15 1.9 Solar Neutrino Oscillation Landscape before KamLAND . ..... 16 2 KamLAND 18 2.1 IdeaoftheExperiment.......................... 18 2.2 KamLANDDetector ........................... 20 2.3 First Reactor Antineutrino Result . .. 23 2.4 Second Reactor Antineutrino Result . .. 26 2.5 Observation of Geologically Produced Antineutrinos . ........ 29 2.6 Motivation for Combined Analysis . 31 3 Event Reconstruction 33 3.1 WaveformAnalysis ............................ 33 3.2 MuonTracking .............................. 34 3.3 EnergyReconstruction . .. .. 35 3.4 VertexReconstruction . .. .. 35 4 Reactor Antineutrinos 36 4.1 ReactorsaroundKamLAND . 36 4.2 ReactorAntineutrinoComponents . 37 4.3 Inverse Beta Decay Cross Section . 39 4.4 SpectrumDistortion ........................... 41 4.5 Instantaneous Spectrum Calculation . .. 42 vii 5 Terrestrial Antineutrinos 44 5.1 Sources of Terrestrial Antineutrinos . .... 44 5.2 Terrestrial Antineutrino Spectrum . ... 48 5.3 GoalsoftheStudy ............................ 48 5.4 Terrestrial Antineutrino Flux and Oscillations . ....... 51 6 Backgrounds 52 6.1 Accidentals ................................ 52 6.2 Muon Induced Correlated Background . 57 6.3 Alpha-nCorrelatedBackground . 57 6.4 Reactor and Terrestrial Antineutrino Mutual Backgrounding ..... 59 7 Likelihood Analysis 61 7.1 SimpleLikelihoodModel . 61 7.2 Rate+Time, Rate+Shape and Rate+Shape+TimeAnalyses. 63 7.3 AddingtheBackgrounds . 65 7.4 ParameterEstimationErrors. 66 7.5 Handling the Systematic Uncertainties . ... 67