Search for effects beyond the born approximation in polarization transfer observables in e(over→)p elastic scattering

Area of Science:

• Nuclear physics
• Particle physics
• Quantum electrodynamics

Background:

• Discrepancy exists between proton electric to magnetic form factor ratio (GE/GM) measurements from cross-section and polarization transfer data.
• Two-photon-exchange (TPE) contribution is a potential explanation for this observed discrepancy.
• Exploring physics beyond the one-photon-exchange (Born) approximation is crucial for understanding proton structure.

Purpose of the Study:

• To investigate the proton electric to magnetic form factor ratio (GE/GM) by measuring polarization transfer observables.
• To search for contributions beyond the standard one-photon-exchange approximation in elastic electron-proton scattering.
• To determine the dependence of the ratio R (approximating μpGE/GM) and longitudinal polarization transfer P(ℓ) on the kinematic parameter ε.

Main Methods:

• Measurements of polarization transfer observables in the elastic H(e,e'p) reaction.
• Experiments conducted at three different beam energies for a fixed momentum transfer squared Q²=2.5 GeV².
• Analysis spanning a wide range of the ε kinematic parameter to probe for deviations from the Born approximation.

Main Results:

• The ratio R (μpGE/GM) was found to be independent of ε within a 1.5% precision.
• An enhancement of (2.3±0.6)% in the longitudinal polarization transfer component P(ℓ) was observed at large ε values.
• These results indicate a deviation from the predictions of the Born approximation at high ε.

Conclusions:

• The observed enhancement in P(ℓ) suggests the presence of physics beyond the one-photon-exchange mechanism.
• The findings provide evidence for potential two-photon-exchange contributions or other higher-order effects.
• Further theoretical and experimental studies are needed to fully elucidate the implications of these results for proton structure and electroweak interactions.