Διερεύνηση ύπαρξης τετραπολικού σθένους στη διέγερση του Δ^+ (1232) με μετρήσεις συναρτήσεων απόκρισης στην αντίδραση H (e, e' p) π^0

Abstract

The subject of the thesis is the search for quadrupole strength in the excitation of the first resonance, Δ^+(1232), of the proton.This strength is related with the shape of the proton, and therefore with the details of its structure; if the proton is not spherical, then it contributes to the quadrupole strength of the Δ^+ excitation. The search for quadrupole strength is based on measurements of electromagnetic response functions in the reaction Η(e,e' p)π^0, of neutral π-meson (π^0) production by electron (e) scattering on liquid hydrogen (H), where the scattered electrons (e') and the recoiling protons (p) of the reaction are detected in coincidence. The data from the measurements are characterized by unprecedent precision in the experimental study of the Δ^+ excitation through electron scattering, and also by strong sensitivity to the quadrupole strength. The results of the analysis of the data with modern theoritical models undoubtedly show that the proton is deformed. In addition, for the first time, the analysis systematically explores the relatively large theoretical uncertainties in the quantitative determination of the deformation, which are related with the understanding of the complicated mechanism of the reaction H (e, e' p)π^0.