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Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures
Published on: October 9, 2012
Transverse beam spin asymmetries in forward-angle elastic electron-proton scattering
D S Armstrong1, J Arvieux, R Asaturyan
1Department of Physics, College of William and Mary, Williamsburg, Virginia 23187, USA.
Physical Review Letters
|October 13, 2007
Summary
We measured electron-proton scattering asymmetry, finding results align with inelastic states, not just elastic ones. This asymmetry probes crucial imaginary components in two-photon exchange amplitudes.
Area of Science:
- Nuclear Physics
- Particle Physics
- Quantum Electrodynamics
Background:
- Precision electron-scattering experiments are vital for understanding fundamental particle interactions.
- The two-photon exchange amplitude is crucial for interpreting scattering data, but its imaginary component is not fully understood.
- Previous models often focused on elastic intermediate states, potentially oversimplifying the complex interactions.
Purpose of the Study:
- To measure the beam-normal single-spin asymmetry in elastic electron-proton scattering.
- To investigate the contributions of inelastic hadronic intermediate states to this asymmetry.
- To provide data that probes the imaginary part of the two-photon exchange amplitude.
Main Methods:
- Scattering 3 GeV transversely polarized electrons off unpolarized protons.
- Measurements were conducted at specific squared momentum transfers (Q2) of 0.15 and 0.25 (GeV/c)2.
- Analysis focused on the beam-normal single-spin asymmetry (A(n)).
Main Results:
- The measured asymmetry deviates from predictions based solely on elastic nucleon intermediate states.
- Experimental results show better agreement with theoretical calculations including significant inelastic hadronic intermediate state contributions.
- The data directly probes the imaginary component of the two-photon exchange amplitude.
Conclusions:
- Inelastic hadronic intermediate states play a significant role in electron-proton scattering asymmetry.
- Accurate description of the two-photon exchange amplitude requires incorporating these inelastic contributions.
- The findings are important for refining theoretical models used in precision electron-scattering experiments.
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