For photon virtualities of <math><mrow><msup><mrow><mi>Q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>≳</mo><mn>20</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>, the results of the (hard Pomeron) fit in the tensor-Pomeron model in terms of the variables, <math><msup><mi>Q</mi><mn>2</mn></msup></math>, and the virtual-photon-proton energy squared, <math><msup><mi>W</mi><mn>2</mn></msup></math>, provide empirical evidence for the validity of the color dipole picture (CDP). Consistency of the CDP with the perturbative QCD (pQCD) improved parton model implies the prediction of <math><msub><mi>C</mi><mn>2</mn></msub><mo>=</mo><msub><mi>ε</mi><mn>0</mn></msub><mo>≅</mo><mn>0.30</mn></math> for the exponent <math><msub><mi>C</mi><mn>2</mn></msub></math> of the energy-squared dependence in agreement with the results of the fits. For <math><mrow><msup><mrow><mi>Q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>≲</mo><mn>20</mn><mi>G</mi><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>, the CDP yields a parameter-free smooth transition from <math><mrow><msup><mrow><mi>Q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>≳</mo><mn>20</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math><msup><mi>Q</mi><mn>2</mn></msup><mo>=</mo><mn>0</mn></math> photoproduction, in distinction from the tensor-Pomeron model that relies on the additional parameter quantifying the intercept of the soft-Pomeron trajectory.

Germany

Dieter Schildknecht

Color-dipole picture versus hard pomeron in deep inelastic scattering

Recent work by Block et al. on the energy-invariant edge in proton-proton scattering is interpreted by quantitatively introducing an energy-dependent black-disk fraction of the proton-proton interaction.

The energy-dependent black-disk fraction in proton-proton scattering

Based on the color-dipole picture, we present a successful parameter-free prediction for the recent high-energy J/ψ photoproduction data from the Large Hadron Collider. The experimental data provide empirical evidence for the transition from color transparency to saturation.