The Color Dipole Picture and the Ratio of the Longitudinal to the Transverse Photoabsorption Cross Section
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)=sigmaL/sigmaT=0.375, or, equivalently, FL/F2=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.
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