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A Search for Narrow States in Radiative Upsilon Decays*

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A Search for Narrow States in Radiative Upsilon Decays* SLAC-307 UC-34D CJW) A SEARCH FOR NARROW STATES IN RADIATIVE UPSILON DECAYS* Stephen T. Lowe+ Stanford Linear Accelerator Center Stanford University Stanford, California 943O5 December 1986 Prepared for the Department of Energy under contract number DE-AC03-76SF00515 Printed in the United States of America. Available from the National Techni- cal Information Service, US. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22161. Price: Printed Copy A07, Microfiche AOl. * Ph.D. dissertation. Work supported in part by the Department of Energy, contract DE-AC03-76SF00515 and 1 + DE-AC03-76SF00098. ABSTRACT A search for new states produced in radiative T(lS) decays is accomplished /by observing the inclusive photon energy spectrum. A narrow resonance in the energy spectrum indicates the existence of a new state X produced by the process ‘Y’ + 7X. The analysis is based on approximately 0.44 x lo6 T(lS) events /produced at the DORIS II e+e- storage ring. These data were collected with the I /Crystal Ball detector between April 1983 and May 1986. This analysis finds no evidence for a new state, so upper limits on the branch- ing ratio BR(T + 7X) are derived, assuming the state X decays primarily to high-multiplicity hadronic final states. In particular, if the state X were a min- imal Higgs particle, its primary decay mode would be to the heaviest fermion- antifermion pair energetically available. For the radiative ‘Y (IS) decays studied here, the heavy fermions would be CFor ss quark states, over most of the relevant Higgs’ mass range. The resulting upper limit for BR(Y’( IS) + 7X) is highly energy dependent but for X mass between 1.5 GeV and 8.0 GeV, the 90% confidence level upper limit is better than 8.0 x 10-4. For a Higgs’ mass near 5.0 GeV, the upper limit is about 2.0 x 10m4which is approximately equal to the lowest order calculation for the Wilczek mechanism. The Wilczek calculation with QCD radiative corrections predict branching ratios below the limits set here for all Higgs’ masses. ACKNOWLEDGEMENTS Experiments in High Energy Physics (HEP) are a collaborative effort and as such require the efforts of many. For their contribution to the experiment and to my education, I sincerely thank all those involved in the Crystal Ball experiment. Special thanks go to my advisor, Elliott Bloom, for his great enthusiasm for physics, his encouragement and guidance over the years, and his constant source of ideas (his editorial talents are also greatly appreciated). Mastering the broad range of techniques needed in experimental physics re- quires many instructors. For teaching me the hands-on nitty-gritties of exper- imental HEP, I thank Gary Godfrey, Bill Lockman, Frank Porter, Bob Clare, John Tompkins, Andreas Schwarz and Susan Cooper. I also want to thank those who shared this learning experience with me, in particular, John Butler, Ray Cowan, Chad Edwards, Gunter Folger, John Gaiser, David Gelphman, Gabi Glaser, Stefan Keh, Roger Lee, Steve Leffler, Harry Nelson, Duncan Prindle, Les Rosenberg, Peter Schmitt, Wim Walk and David Williams. The work needed to typeset this thesis was considerably reduced and the appearance greatly enhanced by the TEX wizard, Ray Cowan. His open willing- ness to help out anytime is very much appreciated. I also thank Ingrid Clare for help handling tapes and the data on them, and June Belew for her secretarial assistance. For his help throughout graduate school, his discussions on Life, God and the world, and his active sense of humor, I want to thank the other member of the Steve doublet, Steve Lefller. Our sharing of survival tactics and strategies helped considerably. Ill For her friendship, honesty and teaching me a little about rationality (and putting up with me during shifts), I thank Patty McBride. Exploring the restau- rants and swimming pools of Hamburg together made life there enjoyable. I want to thank the “Friendly as Always” Achim Irion for improving the quality of life both in Hamburg and Palo Alto. His flair for hosting great par- ties, his skill as a pilot, and his tough determination to spend lunch tanning at DeGuerre pool, even in the face of a slight breeze, will be remembered. For being good friends and discussion partners, I want to thank the very charming sisters, Alyssa Higashi and Andrea Higashi. Away from work, I want to thank Janet Atwood and Miguel Vargas for being friends of the highest quality. I also thank Chris Peck for sharing life for the first several years of graduate school and a lot of unforgettable experiences. For starting me off in the scientific direction I thank Mr. Ray Williams and Dr. Evelyn Banks. Of course my greatest appreciation is for the love and support I’ve received from my parents and family. My mother and father, Roberta and Carol Lowe, and my brother, Michael Lowe, deserve my deepest thanks. I also want to rec- ognize the love and encouragement I’ve received from my grandparents, Winnie and Don Lowary, and Pauline and Cecil Lowe. Finally, I wish to dedicate this thesis to the memory of Don Lowary. iv Table of Contents 1. INTRODUCTION AND SUMMARY ................ 1 1.1 The Standard Model ........................... I 1.2 The Higgs Sector ............................. 8 1.3 Searching for the Higgs Boson in Radiative Upsilon Decays .... 1s 1.4 Experimental Results .......................... 17 1.5 Summary ................................ .21 References . 28 2. THE CRYSTAL BALL EXPERIMENT ............... 25 2.1 Introduction ................................ 25 2.2 The DORIS II Storage Ring ....................... 25 2.3 Experimental Overview ......................... 27 2.4 TheMainBall ............................. .28 2.5 Endcaps .................................. $1 2.6 Tracking Chambers ............................ Sl 2.7 Luminosity Counters ........................... $9 2.8 Time of Flight System .......................... 34 2.9 On-line Data Acquisition System .................... $4 2.10 Off-line Crystal Calibration ....................... 57 2.11 Crystal Ball Jargon ........................... 58 References . .40 V Table of Contents Page vi 3. DATA PROCESSING ........................... 41 3.1 Off-line Analysis ............................. 41 3.2 Data Reduction and Compression ................... 45 3.3 Additional Data Processing ....................... #6 3.4 Hadron Selection ............................. 47 3.5 Monte Carlo Simulations ........................ 47 References .................................... .49 4. THE r(lS) PHOTON SPECTRUM .................. 50 4.1 The r(lS) Data Set ........................... 50 4.2 Determining Cuts Which Optimize Sensitivity ............ 55 4.3 TheCuts ................................ .58 4.3.1 Charge/Neutral Separation .................... 58 4.3.2 Photon Pattern Cuts ....................... 62 4.3.3 Particle Overlap Cut ....................... 71 4.3.4 Low-Energy 7r” Subtraction ................... 71 4.3.5 Notes on Final Cuts ....................... 73 4.4 The Y(lS) Photon Spectrum ...................... 75 4.5 Photon Efficiency Calculation ...................... 78 4.6 Results ................................... 80 4.7 Conclusions ................................ 89 References ..................................... 87 Appendix A. Problems in the Crystal Energy Distributions .... 88 A.1 TheSymptom ............................... 88 A.2 The Problem Found ........................... 91 A.3 Measurement of the Non-linear Response .............. 100 A.4 Modeling the Problem ......................... 103 A.5 Results of CIS Measurements ...................... IO7 Appendix B. Information Useful for Combining Data Sets ... 112 B.l Information Useful for Combining Data Sets ............ 112 Figure Captions [I.11 The effective potential after radiative corrections in the stan- dard model. .................................. 9 [ I.21 Feynman diagram for Higgs production via 2’ bremsstrahlung. ............................... 14 [l.3] Feynman diagram for the Wilczek mechanism. .............. 16 [IA] The branching ratio for Y + 7 + H predicted by the Wilczek mechanism. .................................. 16 [1.5] The final Y(lS) inclusive photon spectrum. ................ 17 [1.6] The 9Oyo confidence level upper limit for the process Y (1s) + 7X as a function of photon energy. .................... 18 - [1.7] ThegO?’o confidence level upper limit for the process Y( IS) + 7X as a function of recoil mass. ....................... 19 [1.8] The upper limit for BR(Y + 7X) as a function of photon energy reported by the ARGUS collaboration. .............. 20 [1.9] The upper limit for BR(Y + 7X) as a function of photon energy reported by the CLEO collaboration. ............... 21 [l.lO] The upper limit for BR(Y + 7X) as a function of recoil mass squared reported by the CUSB collaboration. .............. 22 [2.1] Layout of the DORIS II storage ring. ................... 26 [2.2] The major components of the Crystal Ball at DORIS II. ........ 27 (2.31 The underlying structure of the Crystal Ball. ............... 29 [2.4] The Crystal Ball tube chambers. ...................... 92 [2.5] The Crystal Ball on-line data acquisition system. ............ 95 [2.6] A close-up projection of the Crystal Ball for a typical EM shower. .................................... $9 Vii Figure Captions Page viii [%I] Definition of Connected Regions and Bumps. , . 43 [4.1] The integrated luminosity collected on the Y (1s) by the Crys- tal Ball. 51 [4.2] The number of selected hadrons per selected Bhabha. .......... 52 [4.3] A peak in an
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