THE OBSERVATION OF THE WEAK RADIATIVE HYPERON DECAY ktev.fnal.gov/public/pubs/ktev/caslampig/ping_ OBSERVATION OF THE WEAK RADIATIVE HYPERON DECAY ... friendship, support, and

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  • THE OBSERVATION OF THE WEAK RADIATIVE

    HYPERON DECAY at KTEV/E799,

    FERMILAB

    by

    HUICAN PING

    A dissertation submitted in partial fulfillment of the

    requirements for the degree of

    DOCTOR OF PHILOSOPHY

    (PHYSICS)

    at the

    UNIVERSITY OF WISCONSIN - MADISON

    2005

  • i

    Acknowledgments

    Many people contributed to this thesis in a number of ways. Without them, this

    work would not have been possible. I would like to take this time to thank them.

    First and foremost, I would like to express my deepest gratitude to my major

    advisor Professor Albert Erwin for his continued guidance and advice during all

    of the years of my research. I will always be deeply grateful for his generosity in

    helping me achieve my goals. I have been very lucky to have the opportunity to

    learn from him.

    I want to express my gratitude to Prof. Charles J. Goebel at the Physics De-

    partment of University of Wisconsin Madison. He gave us a theoretical calculation

    of the Branching Ratio for our signal mode . It is very important for

    me to fulfill this project.

    I would also like to thank my lab colleagues in Madison. Professor, Theodoros

    Alexopoulos taught me high energy physics, data analysis, computers, and most

    importantly work ethics during my first 2 years in Madison. Dr. Christos Velisaris

    also gave me useful suggestions and helps during the process of doing data analysis

    in the last 3 years.

    I am indebted to all of the KTeV collaborators. I would like to give thanks to

    the hyperon group: E.J. Ramberg, E. Monnier, D.A. Jensen etc. I am grateful for

  • ii

    the financial support from the Department of Energy.

    I really appreciate the help from the hardworking staff at the physics depart-

    ment B. Schutz, J. Buehlman, A. Lefkow and T. Sherron for making things really

    work for me.

    I dont know how to express my appreciation to my wife, Gangjuan Jiang,

    whose love, friendship, support, and devotion are beyond description.

  • Contents

    Abstract xv

    1 Introduction 1

    1.1 The Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . 2

    1.2 Some Basic Facts about Hyperons . . . . . . . . . . . . . . . . . . . 3

    1.3 Phenomenology of . . . . . . . . . . . . . . . . . . . . . 6

    1.4 2-Body Weak Radiative Hyperon Decays . . . . . . . . . . . . . . . 9

    1.5 2-Body WRHD Experimental Results Prior to 2002 . . . . . . . . . 11

    1.6 3-Body Weak Radiative Hyperon Decay . . . . . . . . 13

    2 The beamline and KTeV detector 18

    2.1 The Beamline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    2.1.1 Proton Beam . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    2.1.2 Target and KTeV Coordinate System . . . . . . . . . . . . . 19

    2.1.3 Sweeping Magnet, Absorbers . . . . . . . . . . . . . . . . . . 21

    2.1.4 Collimating System . . . . . . . . . . . . . . . . . . . . . . . 22

    2.1.5 Spin rotator magnet . . . . . . . . . . . . . . . . . . . . . . 23

    2.1.6 The Secondary Beam . . . . . . . . . . . . . . . . . . . . . . 23

    2.2 The Main E799 Detector Brief Introduction . . . . . . . . . . . . . 25

    iii

  • iv

    2.3 The Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

    2.3.1 Analyzing Magnet . . . . . . . . . . . . . . . . . . . . . . . 29

    2.3.2 Drift Chambers . . . . . . . . . . . . . . . . . . . . . . . . . 29

    2.4 The Transition Radiation Detectors . . . . . . . . . . . . . . . . . . 33

    2.5 The Trigger Hodoscopes . . . . . . . . . . . . . . . . . . . . . . . . 37

    2.6 The Photon Veto System . . . . . . . . . . . . . . . . . . . . . . . . 38

    2.6.1 Ring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . 38

    2.6.2 Spectrometer Antis . . . . . . . . . . . . . . . . . . . . . . . 39

    2.6.3 Cesium Iodide Anti and Collar Anti . . . . . . . . . . . . . . 41

    2.7 The Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . 42

    2.7.1 The Purpose of CsI . . . . . . . . . . . . . . . . . . . . . . . 42

    2.7.2 The CsI Crystals . . . . . . . . . . . . . . . . . . . . . . . . 42

    2.7.3 The PMT and DPMT . . . . . . . . . . . . . . . . . . . . . 45

    2.7.4 The resolution of CsI . . . . . . . . . . . . . . . . . . . . . . 47

    2.8 The Hole Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

    2.9 The Hadron Anti . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

    2.10 The Muon System . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

    3 The Trigger System and the Run 53

    3.1 Level 1 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

    3.2 Level 2 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

    3.2.1 The Stiff Track Trigger . . . . . . . . . . . . . . . . . . . . . 55

    3.3 Level 3 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

    3.4 Hyperon Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

  • v

    3.5 The Runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

    4 Event Reconstruction 62

    4.1 Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

    4.1.1 Hit pairs and SODs . . . . . . . . . . . . . . . . . . . . . . . 63

    4.1.2 The X and Y Track Candidates . . . . . . . . . . . . . . . . 66

    4.1.3 Finding Y tracks . . . . . . . . . . . . . . . . . . . . . . . . 66

    4.1.4 Finding X tracks . . . . . . . . . . . . . . . . . . . . . . . . 67

    4.1.5 Track Vertex Candidates . . . . . . . . . . . . . . . . . . . . 67

    4.1.6 Track-Cluster matching . . . . . . . . . . . . . . . . . . . . . 68

    4.2 Cluster Finding, HCC algorithm . . . . . . . . . . . . . . . . . . . . 69

    4.2.1 Cluster Position . . . . . . . . . . . . . . . . . . . . . . . . . 70

    4.3 Energy Measurement in CsI . . . . . . . . . . . . . . . . . . . . . . 71

    4.4 Electron and identification . . . . . . . . . . . . . . . . . . . . . 72

    4.4.1 Using CsI Calorimeter . . . . . . . . . . . . . . . . . . . . . 72

    4.4.2 Using TRD . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

    5 Monte Carlo Simulation and Background Studies 76

    5.1 3 Steps of Event Generation . . . . . . . . . . . . . . . . . . . . . . 76

    5.2 MC of Beam Production at target . . . . . . . . . . . . . . . . . . . 77

    5.2.1 Hyperon Production . . . . . . . . . . . . . . . . . . . . . . 77

    5.2.2 Kaon Production . . . . . . . . . . . . . . . . . . . . . . . . 77

    5.3 Simulation of Decay Process . . . . . . . . . . . . . . . . . . . . . . 80

    5.3.1 Distribution of Hyperon Non-Leptonic Decays . . . . . . . . 81

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    5.3.2 Polarization of Hyperon Non-Leptonic Decays . . . . . . . . 81

    5.4 Detector Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

    5.4.1 Drift Chamber . . . . . . . . . . . . . . . . . . . . . . . . . 82

    5.4.2 TRDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

    5.4.3 The Trigger Hodoscopes . . . . . . . . . . . . . . . . . . . . 84

    5.4.4 CsI Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . 84

    5.5 Accidental Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

    6 The Normalization Mode Analysis 90

    6.1 Data Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

    6.2 The Reconstruction Methods . . . . . . . . . . . . . . . . . . . . . . 91

    6.2.1 The cuts for Normalization Mode . . . . . . . . . . . . . . . 93

    6.3 Data and MC comparison . . . . . . . . . . . . . . . . . . . . . . . 97

    6.4 Acceptance and Flux . . . . . . . . . . . . . . . . . . . . . . . . . . 105

    6.4.1 Flux calculation from Trigger 11 events . . . . . . . . . . . . 105

    6.4.2 Flux calculation from Trigger 10 events . . . . . . . . . . . . 106

    7 The Signal Mode Analysis 108

    7.1 The Reconstruction Methods . . . . . . . . . . . . . . . . . . . . . . 109

    7.2 Same Cuts for Signal Mode and Normalizatoin mode . 110

    7.3 More Cuts: Find combination . . . . . . . . . . . . . . . . . . 114

    7.4 Drift Chambers Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . 116

    7.5 Rejection of Accidental Photons in the Calorimeter . . . . . . . . . 118

    7.6 M0 Cut Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 122

  • vii

    7.7 TRD Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

    7.8 Coplanarity Cuts Discussion . . . . . . . . . . . . . . . . . . . . . . 124

    7.9 4 Candidate Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

    8 Background and Hadron Anti Correction 134

    8.1 Lambda Background . . . . . . . . . . . . . . . . . . . . . . . . . . 134

    8.2 Cascade Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . 135

    8.2.1 followed by Radiative Lambda decay p 135

    8.2.2 followed by p plus accidental one . . . 136

    8.2.3 followed by p plus accidental one . . 138

    8.2.4 followed by and p plus an ac-

    cidental . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

    8.3 Kaon Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

    8.3.1 KL + . . . . . . . . . . . . . . . . . . . . . . . . . . 139

    8.4 Backgrounds After Selection Criteria . . . . . . . . . . . . . . . . . 140

    8.5 Hadron-Anti correction for the candidate events . . . . . . . . . . . 141

    9 Systematics 146

    9.1 Old and New MC Comparison . . . . . . . . . . . . . . . . . . . . . 146

    9.2 Systematics by Monte Carlo Simulation .