Measurement of the pion exclusive electro-production cross-section in the E12-19-006 experiment in Hall-C at Jefferson Lab

Abstract

One of the most effective methods for exploring the transition from hadronic de- grees of freedom to quark-gluon degrees of freedom in Quantum Chromodynamics (QCD) is through the investigation of \exclusive" pion and kaon electro-production reactions at various Q2 and -t values. The E12-19-006 experiment is conducted within the confines of experimental Hall C at the Thomas Jefferson National Accel- erator Facility, USA, for such studies. The primary aim of the experiment is to first enhance our comprehension of the pion electro-production cross-section and its form factor at Q2 = 0.38 and 0.42 GeV2. This is the first run period of the E12-19-006 experiment which ran in summer 2019. A more profound understanding of the pion electro-production reaction, 1H(e,e'π+)n, at low Q2 is deemed essential to employ this electro-production reaction (an indirect technique) for the high Q2 studies, thereby delving deeper into the realm of QCD. Consequently, this dissertation presents a thorough analysis of the experimental data acquired in the first run period of the E12-19-006 experiment. In pursuit of precision, a series of systematic studies (target boiling correction study, the elastic reaction cross-section measurements, study for determining vari- ous kinematics offsets, etc.) are conducted to discern the accuracy of the analyzed data, a prerequisite for the use of Rosenbluth separation technique to separate the pion electro-production cross-section terms in t bins. The separated pion electro- production cross-section through the Rosenbluth separation technique is then used to extract the pion electromagnetic form factor. In this dissertation, the pion electro-production cross-section is carefully dissected into its four constituent components: longitudinal (𝜎L), transverse (σT ), longitudinal- transverse (σLT ), and transverse-transverse (σTT ), using the full version of Rosenbluth separation technique for the Q2 = 0.38 GeV2. The technique is simultaneously fitted to the unseparated pion electro-production cross-sections at the three values of polar- ization of the virtual photon (ϵ), i.e., ϵ = 0.286, 0.629 and 0.781. An iterative process is applied to refine the parameters of the model cross-sections until the yield ratio of experimental and Monte Carlo simulation converges. In this study, 21 iterations are conducted to refine the model cross-section parameters. The final pion electro- production cross-section terms are then determined for 7 t bins using the optimized parameters of the model cross-sections.