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Coherent Ρ Meson Electroproduction Off Deuteron FLORIDA INTERNATIONAL UNIVERSITY Miami, Florida COHERENT RHO MESON ELECTROPRODUCTION OFF DEUTERON A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in PHYSICS by Atilla Gönenç 2009 1 To: Dean Kenneth Furton College of Arts and Sciences This dissertation, written by Atilla Gönenç, and entitled Coherent Rho Meson Electroproduction off Deuteron, having been approved in respect to style and intellectual content, is referred to you for judgment. We have read this dissertation and recommend that it be approved. _______________________________________ Werner U. Boeglin _______________________________________ Cem Karayalcin _______________________________________ Laird Kramer _______________________________________ Misak Sargsian _______________________________________ Brian A. Raue, Major Professor Date of Defense: June 24, 2008 The dissertation of Atilla Gönenç is approved. _______________________________________ Dean Kenneth Furton College of Arts and Sciences _______________________________________ Dean George Walker University Graduate School Florida International University, 2009 ii © Copyright 2009 by Atilla Gönenç All rights reserved. iii DEDICATION This dissertation is dedicated to my wonderful parents, Tulin and Hasim, for their love and endless support… iv ACKNOWLEDGMENTS Though only my name appears on the cover of this dissertation, a great many people have contributed to its creation. The writing of this dissertation has been truly a challenge and I owe my thanks to all those who gave me the possibility to complete it. My deepest gratitude is to my advisor, Dr. Brian Raue. His guidance, patience and support helped me overcome many crisis situations and finish this dissertation. Most importantly, none of this would have been possible without the love and patients of my family. My immediate family, to whom this dissertation is dedicated to, has been source of love, support and strength all these years. I am also thankful to my wife Maryam for her unwavering support. v ABSTRACT OF THE DISSERTATION COHERENT RHO MESON ELECTROPRODUCTION OFF DEUTERON by Atilla Gönenç Florida International University, 2009 Miami, Florida Professor Brian A. Raue, Major Professor QCD predicts Color Transparency (CT), which refers to nuclear medium becoming transparent to a small color neutral object produced in high momentum transfer reactions, due to reduced strong interaction. Despite several studies at BNL, SLAC, FNAL, DESY and Jefferson Lab, a definitive signal for CT still remains elusive. In this dissertation, we present the results of a new study at Jefferson Lab motivated by theoretical calculations that suggest fully exclusive measurement of coherent rho meson electroproduction off the deuteron is a favorable channel for studying CT. Vector meson production has a large cross section at high energies, and the deuteron is the best understood and simplest nuclear system. Exclusivity allows the production 2 and propagation to be controlled separately by controlling Q , lf (formation length), lc (coherence length) and t. This control is important as the rapid expansion of small objects increases their interaction probability and masks CT. The CT signal is investigated in a ratio of cross sections at high t (where re-scattering is significant) to low t (where single nucleon reactions dominate). The results are presented over a Q2 range of 1 to 3 GeV2 based on the data taken with beam energy of 6 GeV. vi TABLE OF CONTENTS CHAPTER PAGE 1 Theoretical Background and Motivation ................................................................................. 5 1.1 Color Transparency .......................................................................................................... 5 1.2 Basic Aspects of Color Transparency .............................................................................. 7 1.3 Coherent Vector Meson Production ................................................................................. 8 1.4 Experimental Objectives ................................................................................................ 11 1.5 Previous Data and Measurements .................................................................................. 13 1.5.1 Color Transparency in A(p,2p) .............................................................................. 13 1.5.2 Color Transparency in A(e,e’p) ............................................................................. 15 1.5.3 Color Transparency in A( , dijet) ........................................................................ 16 1.5.4 Color Transparency in A( , ' ) ......................................................................... 17 1.5.5 Color Transparency in A(, p ) .......................................................................... 18 1.5.6 Color Transparency in A(ee , ' ) ....................................................................... 19 2 Experimental Setup ................................................................................................................ 22 2.1 Jefferson Lab .................................................................................................................. 22 2.2 CLAS Detector, Target, and Trigger ............................................................................. 23 3 Particle Identification and Event Selection ............................................................................ 26 3.1 Data Quality ................................................................................................................... 26 3.2 Corrections ..................................................................................................................... 30 3.2.1 Energy Loss and Momentum Corrections ............................................................. 30 3.2.2 Electron Beam Energy Correction ......................................................................... 34 3.2.3 Vertex correction ................................................................................................... 35 3.3 Particle Identification ..................................................................................................... 36 3.3.1 Scattered Electron Identification ............................................................................ 36 3.3.2 Hadron Identification ............................................................................................. 49 3.4 Additional Cuts .............................................................................................................. 56 3.4.1 Bad scintillator paddle removal ............................................................................. 56 3.4.2 W invariant mass cut .............................................................................................. 57 4 Yield Corrections, Extraction and Systematic Uncertainties ................................................. 59 4.1 Data Correction Factors ................................................................................................. 59 4.1.1 Acceptance ............................................................................................................. 59 4.1.2 Other Correction Factors ........................................................................................ 62 4.2 Data Normalization ........................................................................................................ 65 4.3 Yield Extraction ............................................................................................................. 67 4.3.1 Mass spectrum of the ρ particle ............................................................................. 67 4.3.2 The Fitting Method ................................................................................................ 68 4.3.3 Understanding the background .............................................................................. 70 4.3.4 Uncertainties .......................................................................................................... 72 5 Results and Discussions ......................................................................................................... 76 5.1 The Differential Cross Section ....................................................................................... 76 5.2 CT ratio .......................................................................................................................... 78 vii 5.3 Check of SCHC.............................................................................................................. 80 5.4 Ratio of longitudinal to tranverse cross section ............................................................. 81 5.5 Summary and Conclusions ............................................................................................ 85 REFERENCES .............................................................................................................................. 86 VITA .............................................................................................................................................. 89 viii LIST OF FIGURES FIGURE PAGE 1. Graphical representation of the rho electroproduction................................................................. 2 2. Graphical representation of coherence and formation lengths ..................................................... 4 3. Interaction probability of ultra-relativistic ee pairs. ................................................................ 6 4. Graphical
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