Measurement of the ratio of the Sachs form factors of the proton at the psi-prime resonance

In the experiment E835 conducted at Fermi National Accelerator Laboratory, proton-antiproton annihilation was studied using a stochastically cooled antiproton beam incident on an internal hydrogen gas jet target. The E835 detector was optimized for the detection of electromagnetic final states (e +, e+ and γ) in the presence of a large hadronic background. We collected 22.57 pb−1 of data at the center-of-mass energy of the $y\prime$ resonance (3686 MeV) during two separate periods of data taking. In these data there was a subset of 6844 exclusive e +e− events, the analysis of which is the subject of this thesis. The reaction p¯p → e+e− probes the electromagnetic structure of the proton, which can be represented by the Sachs form factors G_E and G_M. These form factors have been well measured as a function of momentum transfer squared (q2) in the space-like region ( q2 < 0). In the time-like region (q 2 ≥ $4M2p$), the experiments are more difficult due to the rapid fall-off in the p¯p cross section. In this thesis the first measurement of the angular distribution of the process p¯p → e+e− at the $y\prime$ resonance is described and from this result the value of $GEGM$ was determined to be $0.87+0.25-0.24$.