The Color Dipole Picture and the Ratio of the Longitudinal to the Transverse Photoabsorption Cross Section

TL;DR

This paper predicts a model-independent ratio of longitudinal to transverse photoabsorption cross sections based on the color dipole picture, and confirms the prediction with experimental data from HERA.

Contribution

It introduces a model-independent prediction for the ratio R(W2,Q2) in deep inelastic scattering based on the transverse size reduction of q q-bar fluctuations.

Findings

Predicted ratio R(W2,Q2)=0.375 for large Q2 and small x.

Experimental data from HERA confirm the size reduction effect.

Provides a theoretical basis for understanding photon fluctuations in deep inelastic scattering.

Abstract

The transverse size of q q-bar fluctuations of a longitudinally polarized photon is reduced relative to the transerve size of q q-bar fluctuation of a transversely polarized photon. This implies a model-independent prediction of the ratio R(W2,Q2)=sigma_L/sigma_T=0.375, or, equivalently, F_L/F_2=0.27, for x=Q2/W2<<1 and Q2 sufficiently large, while R(W2,Q2)=0.50, if this effect is ignored. Experimental data from HERA confirm the transverse-size reduction.