楊信男臺灣大學：物理研究所陳佑駿Chen, Yu-ChunYu-ChunChen2007-11-262018-06-282007-11-262018-06-282007http://ntur.lib.ntu.edu.tw//handle/246246/54498對於核子波形因子的量測，近代的極化實驗所得的結果，和以前非極化實驗所得的結果對比時，雖在低動量交換時能夠一致，但在高動量交換時卻有巨大的不同。為要解決這個迷題，雙光子交換在彈性電子質子碰撞中的效應開始被注重起來。我們透過部份子的模型，計算雙光子交換的貢獻。我們發現，當加入雙光子交換的貢獻後，能很好的解決之前兩種實驗所得結果嚴重衝突的問題。如今我們明白，雙光子交換的效應，在量測核子的波形因子時伴演了很重要的角色。When measuring the nucleon form factors, recent polarization experiments at the Thomas Jefferson Laboratory (JLab) have confirmed the earlier Rosenbluth measurements from SLAC at small Q2. However, at large Q2, a huge discrepancy appear between them. To solve this puzzle, the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering was estimated. And then we thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide angle scattering processes. We find that the interference of one- and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments. Now we know higher-order QED effects can play an important role in precision measurements of nucleon elastic form factors in electron scattering.Acknolwedgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii CHAPTER 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Elastic electron-nucleon scattering in one-photon exchange approximation and the nucleon form factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 Kinematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Form factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.1 Rutherford scattering and Mott scattering . . . . . . . . . . . . . 11 2.2.2 Modified Mott scattering with charge density distribution . . . . . 12 2.2.3 Elastic electron-nucleon scattering from QED . . . . . . . . . . . 15 2.3 Elastic electron-nucleon scattering in one-photon exchange . . . . . . . . 17 3 Elastic electron-nucleon scattering with two-photon exchange . . . . . . . . 21 3.1 General scattering amplitude in elastic electron-nucleon scattering . . . . 21 3.1.1 Scattering amplitude with two-photon exchange process . . . . . 22 3.1.2 General scattering amplitude in two-photon exchange approximation 24 3.2 Observables of the elastic electron-nucleon scattering . . . . . . . . . . . 25 3.3 How to Reconcile the Rosenbluth and the Polarization transfer methods? . 27 3.3.1 The first approximation by using general scattering amplitude . . 27 3.3.2 Two-photon exchange contributions to elastic electron-proton scattering cross sections in a simple hadronic model . . . . . . . . . . 29 3.4 Model independent extraction of two-photon exchange effect . . . . . . . 33 4 Generalized parton distributions formalism . . . . . . . . . . . . . . . . . . 39 4.1 Definition of generalized parton distributions . . . . . . . . . . . . . . . 39 4.2 Form factors sum rules in generalized parton distributions . . . . . . . . . 42 4.3 Gaussian ansatz (G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.4 Small t behavior and Regge parametrization (R1) . . . . . . . . . . . . . 46 4.5 Large t behavior and modified Regge parametrization (R2) . . . . . . . . 47 4.6 Results for different parametrization . . . . . . . . . . . . . . . . . . . . 49 5 Two photon exchange contribution with handbag approximation . . . . . . 53 5.1 Two-photon exchange contribution to elastic electron-quark scattering . . 55 5.2 Results for two-photon exchange contribution to elastic electron-quark scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.3 The handbag calculation of the two-photon exchange contribution to the elastic electron-nucleon scattering . . . . . . . . . . . . . . . . . . . . . 60 5.4 Results for elastic electron nucleon scattering . . . . . . . . . . . . . . . 68 5.4.1 Cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 5.4.2 Polarization transfers . . . . . . . . . . . . . . . . . . . . . . . . 72 5.4.3 Single spin asymmetry . . . . . . . . . . . . . . . . . . . . . . . 72 5.4.4 Positron-proton vs. electron-proton . . . . . . . . . . . . . . . . 74 5.4.5 Possibilities at lower juj . . . . . . . . . . . . . . . . . . . . . . 76 5.4.6 Rosenbluth determinations of GE=GM including 2-photon corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 6 Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 APPENDIX A Cross section and polarization results in the axial-vector representation . . . . 88 A.1 Form factors and observables . . . . . . . . . . . . . . . . . . . . . . . . 88 A.2 Electron-quark elastic scattering amplitudes . . . . . . . . . . . . . . . . 90 A.3 Embedding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 APPENDIX B Quark mass sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 B.1 Kinematics, and imaginary parts of the hard amplitudes . . . . . . . . . . 92 B.2 Real parts of hard two-photon exchange amplitudes with finite quark mass 93 Vita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95972955 bytesapplication/pdfen-US核子波行因子,雙光子交換,彈性核子碰撞,部分子,質子,中子nucleon form factors, two-photon exchange, elastic scattering, partonic, protonthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54498/1/ntu-96-D91222006-1.pdf