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Two-photon exchange in elastic electron-proton scattering: a QCD factorization approach.
Nikolai Kivel1, Marc Vanderhaeghen
1Institute für Theoretische Physik II, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Physical Review Letters
|October 2, 2009
Summary
We calculated the two-photon exchange effect in electron-proton scattering. This leading contribution scales as 1/Q(4) and is model-independently linked to nucleon distribution amplitudes.
Area of Science:
- Nuclear physics
- Particle physics
- Quantum chromodynamics
Background:
- Elastic electron-proton scattering experiments probe the internal structure of protons.
- Discrepancies in scattering data at high momentum transfer suggest contributions beyond one-photon exchange.
- Two-photon exchange is a significant higher-order effect in quantum electrodynamics and quantum chromodynamics.
Purpose of the Study:
- To estimate the two-photon exchange contribution to elastic electron-proton scattering.
- To express the leading two-photon exchange amplitude in a model-independent manner.
- To provide predictions for existing and upcoming scattering experiments.
Main Methods:
- Calculation of the two-photon exchange amplitude at large momentum transfer (Q^2).
- Expressing the amplitude in terms of leading twist nucleon distribution amplitudes.
- Utilizing various models for nucleon distribution amplitudes to derive estimates.
Main Results:
- The leading two-photon exchange amplitude exhibits a 1/Q^4 scaling behavior.
- The amplitude is shown to be expressible in a model-independent way.
- Estimates for existing and ongoing experiments are provided based on different distribution amplitude models.
Conclusions:
- Two-photon exchange is a crucial correction for precise electron-proton scattering measurements.
- The 1/Q^4 scaling provides a pathway for model-independent analysis.
- The provided estimates will aid in the interpretation of experimental results and guide future research.
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