A Study of Particle Identi cation with the Sup er-Kamiokande Detector A Thesis Presented by Karl Florian Go eb el to The Graduate Scho ol in Partial Ful llment of the Requirements for the Degree of Master of Arts in Physics State University of New York at Stony Bro ok Decemb er 1996 State University of New York at Stony Bro ok The Graduate Scho ol Karl Florian Go eb el We, the thesis committee for the ab ove candidate for the Master of Arts degree, hereby recommend acceptance of the thesis. Professor Chiaki Yanagisawa DepartmentofPhysics Professor Chang Kee Jung DepartmentofPhysics Professor George Sterman DepartmentofPhysics This thesis is accepted by the Graduate Scho ol. Graduate Scho ol ii Abstract of the Thesis A Study of Particle Identi cation with the Sup er-Kamiokande Detector by Karl Florian Go eb el Master of Arts in Physics State University of New York at Stony Bro ok 1996 A particle identi cation algorithm has b een develop ed for the study of atmospheric neutrinos with the Sup er-Kamiokande de- tector. Preliminary results are obtained for identifying electrons and muons based on a study with a sample of Monte Carlo events. The identi cation eciency for particles in a visible energy range 100 MeV to 2 GeV is b etter than 93 for electrons and 91 for muons. A preliminary analysis with a selected data sample shows results qualitatively consistent with the Monte Carlo study. iii iv Contents List of Figures : :: :: :: :: ::: :: :: :: :: ::: :: :: ix List of Tables : :: :: :: :: ::: :: :: :: :: ::: :: :: x Acknowledgements :: :: :: ::: :: :: :: :: ::: :: :: xi 1 Intro duction :: :: :: :: :: ::: :: :: :: :: ::: :: :: 1 1.1 Theoretical Background .. ... .. .. .. .. ... .. .. 1 1.2 Sup er-Kamiokande, a Multipurp ose Detector . 3 1.3 Historic Overview and Comparison with other Exp eriments . 5 2 Neutrino Physics : :: :: :: ::: :: :: :: :: ::: :: :: 11 2.1 General Overview . 11 2.2 Neutrino Oscillations . 14 2.3 Atmospheric Neutrinos . 17 2.4 Interaction with Matter .. ... .. .. .. .. ... .. .. 21 v 3 Detector Description : :: :: ::: :: :: :: :: ::: :: :: 30 3.1 Basic Principle of a Water Cerenkov Detector . ... .. .. 30 3.2 The Water Tank .. .. .. ... .. .. .. .. ... .. .. 32 3.3 Photomultipliers .. .. .. ... .. .. .. .. ... .. .. 35 3.4 Trigger System and Data Acquisition . 38 4 Analysis :: ::: :: :: :: :: ::: :: :: :: :: ::: :: :: 44 4.1 Monte Carlo . 44 4.2 Fitting . 48 4.3 Particle Identi cation . 53 4.4 Event Selection . .. .. .. ... .. .. .. .. ... .. .. 76 4.5 Comparison with Data . .. ... .. .. .. .. ... .. .. 80 4.6 Conclusion . 83 vi List of Figures 2.1 Primary Cosmic Ray Flux . ... .. .. .. .. ... .. .. 18 2.2 Atmospheric - uxes . 20 2.3 -Flux Ratios .. .. .. .. ... .. .. .. .. ... .. .. 21 2.4 Feynman Diagrams for Elastic e Scattering .. ... .. .. 23 2.5 Feynman Diagrams for Quasi-Elastic N Scattering . 24 2.6 Feynman Diagrams for Inelastic N Scattering . 24 2.7 Cross Section of Charged-Current quasi-elastic interactions . 25 2.8 Cross Section for CC Single-Pion Pro duction . 26 2.9 Total Cross Section for CC Interactions . 27 2.10 Ratio of and Cross Sections .. .. .. .. ... .. .. 28 e 2.11 Comparison of cross section for free and b ound nucleons .. 29 3.1 Cerenkov geometry . 31 3.2 Schematic diagram of Sup er-Kamiokande . 33 3.3 The 50 cm Photomultiplier Tub e .. .. .. .. ... .. .. 35 3.4 Quantum Eciency of a 50 cm PMT .. .. .. ... .. .. 36 vii 3.5 Inner PMT circuit and signal decoupling .. .. ... .. .. 39 3.6 The analog input circuit of the ATM..... .. ... .. .. 41 3.7 Schematic diagram of the Data Acquisition system. ...... 42 4.1 Neutrino ux at Cleveland and Kamioka .. .. ... .. .. 47 4.2 Point source and Cerenkov light................. 50 4.3 Position resolution of YASTEF ................. 54 4.4 Scan of an electron . .. .. ... .. .. .. .. ... .. .. 56 4.5 Scan of a muon . .. .. .. ... .. .. .. .. ... .. .. 57 4.6 Mapping for charge-track-distribution. .. .. ... .. .. 58 4.7 Charge-track-distribution for a \typical" electron. 59 4.8 Charge-track-distribution for a \typical" muon. ... .. .. 60 4.9 Scan of a hard scattered muon in cylindrical p ersp ective. .. 62 4.10 Charge-track-distribution of the ab ove hard scattered muon. 62 4.11 The relevant derivatives for Rispid ............... 64 4.12 Rispid for MC electrons and muons . 66 4.13 Rispid as function of the distance to the wall..... .. .. 67 4.14 Rispid as a function of direction . 69 4.15 Rispid-grid for MC electrons and muons .. .. ... .. .. 70 4.16 Rispid and Rispid-grid distributions for di erent energies . 71 4.17 Rispid-grid as a function of charge . 73 viii 4.18 Collected charge distribution for MC electrons and muons .. 75 4.19 Rispid-grid separation value as a function of charge ...... 76 4.20 Adpid as a function of charge .. .. .. .. .. ... .. .. 77 4.21 Adpid for single ring contained data events... ... .. .. 81 4.22 Adpid for Monte Carlo single ring contained events ...... 82 4.23 Adpid for MC events followed by a decay electron . 84 4.24 Adpid for data events followed by a decay electron . 85 ix List of Tables 1.1 Atmospheric neutrino data from 4 exp eriments.... .. .. 7 1.2 Physical parameters of water Cerenkov detectors . 9 1.3 Performance parameters of water Cerenkov detectors .. .. 10 4.1 Rispid-grid identi cation probability for various energies. 72 x Acknowledgements First, I would like to thank the German-American Fulbright Commission which made my stay in Stony Bro ok p ossible. Here, I had the opp ortunityto work in an active research group in high energy physics whichwas a totally new exp erience for me. The Sup er-Kamiokande exp eriment is a pro duct of many p eople and my work would not have b een p ossible without their contributions. However, some p eople deserve sp ecial mention. First, I thank my advisor Prof. Chiaki Yanagisawa who guided me during this past academic year and whose supp ort was not limited to the eld of physics. I also owe many thanks to Prof. Chang Kee Jung for advise mainly during our weekly meetings. Much of what I know ab out computers I learned from my fellow graduate students Brett Viren and Eric Sharkey. I am thankful to Clark McGrew who shared his broad knowledge and exp erience with me and provided me with many ideas. While writing my thesis I got much supp ort from Jim Hill who revised my rst drafts. Through many discussions he help me broaden my understanding of the physics in Sup er-Kamiokande. I am grateful to Friedrich Konig for reviewing the initial drafts of my thesis. Beyond physics, my staywas enriched by many friends here in Stony Bro ok. Far from home I received continuous supp ort from my family. Their regular corresp ondence, however, never made me feel home was far away. xii 1 Chapter 1 Intro duction 1.1 Theoretical Background For almost 20 years the \Standard Mo del" of elementary particle physics which comprises quantum chromo dynamics and the Glashow-Weinb erg-Salam theory of electroweak pro cesses has b een accepted as the theory describing all elementary interactions except gravity. So far there have b een no com- p elling exp erimental ndings requiring a mo di cation of the current Standard Mo del. However, there is some reason to b elieve that there is physics b eyond the Standard Mo del. Particle interactions are very successfully describ ed in terms of lo cal gauge symmetries. In the Standard Mo del the three fundamental forces re ect three indep endent symmetries. It seems natural to develop theories where these separate symmetries are part of one larger gauge symmetry. 2 From a theoretical p oint of view these grand uni ed theories GUTs are much more satisfying than the Standard Mo del. Certainly one of the most exciting phenomena predicted by GUTs is proton decay. In the Standard Mo del the proton is stable as it is the lightest baryon. It cannot decayinto leptons b ecause baryon numb er is assumed to b e conserved. However there is no underlying symmetry that requires baryon and lepton numb er conservation. In fact most GUTs provide for baryon-lepton interactions. In the framework of grand uni ed theories neutrinos are usually put in a large multiplet together with quarks as well as charged leptons [1]. As neutrinos are treated equally with charged leptons and quarks it is natural to assume that they are also massive particles. In analogy to quarks, massive neutrinos can also have avor mixing. This leads to the p ossibility of the in- teresting phenomenon of neutrino oscillations where neutrinos change their avor state. An observation of neutrino oscillations represents an unambigu- ous evidence for non standard physics. The existence of neutrino mass is also of imp ortance in Cosmology. Because of the large numb er of neutrinos exp ected in the universe, massive neutrinos might considerably contribute to the dark mass. This would have a great impact on the cosmological mo del of the universe. 3 1.2 Sup er-Kamiokande, a Multipurp ose De- tector Sup er-Kamiokande is a 50,000 ton Water Cerenkov Detector in the Kamioka mine in Japan. It detects relativistic charged particles by the Cerenkov light they emit. The detector is lo cated under 1000 meters of mountain ro ck, which can only b e p enetrated by neutrinos and very ener- getic cosmic raymuons. Construction has b een completed and data taking started on April 1st, 1996. Sup er-Kamiokande is suitable to search for manyinteresting phenomena in physics [2]. Solar neutrinos pro duced bynuclear chain-reactions in the core of the sun are within the sensitivity range of the detector [4]. Also, in the case of a nearby sup ernova explosion the corresp onding neutrino burst can b e detected. The particle identi cation program presented in this work is mainly develop ed for the analysis of atmospheric neutrinos. However, it is also relevant to the analysis of proton decay.