Abstract
For photon virtualities of $Q^2 \gsim 20 {\rm GeV}^2$, the results of the (hard Pomeron) fit in the tensor-Pomeron model in terms of the variables $Q^2$ and the virtual-photon-proton energy squared, $W^2$, 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 $C_2 = \epsilon_0 \cong 0.30$ for the exponent $C_2$ of the energy-squared dependence in agreement with the results of the fits. For $Q^2 \lsim 20 GeV^2$, the CDP yields a parameter-free smooth transition from $Q^2 \gsim 20 {\rm GeV}^2$ to $Q^2 = 0$ photoproduction, in distinction from the tensor-Pomeron model that relies on the additional parameter quantifying the intercept of the soft-Pomeron trajectory.
Highlights
We show that consistency of the color dipole picture (CDP) and the perturbative-QCD-improved parton model implies a successful prediction for the numerical value of the exponent of the W2 dependence, ε0 1⁄4 C2 ≅ 0.30
The representation of the photoabsorption cross section in (11) and (12) is a nonperturbative2 one; otherwise, it would not include and contain the smooth transition to the Q2 1⁄4 0 photoproduction cross section. It is the structure of the ðqq Þp-interaction amplitude contained in (12) that is responsible for the CDP prediction of the 1=Q2 dependence of the photoabsorption cross section, σγÃp ∝ 1=Q2 [given in (17) below], that, according to the fit result (1) with (3), is confirmed by the exppeffirffiffiiffimffiffiffieffiffiffinffiffitffiaffiffilffi data
(ii) Requiring consistency of the CDP and perturbative QCD (pQCD) for sufficiently large Q2 ≳ 10 GeV2 yields the prediction of C2 1⁄4 0.29 for the exponent C2 that is confirmed by the CDP fit result of C2 1⁄4 0.27Æ0.01 and the hard-Pomeron-fit result of ε0 ≅ 0.30 Æ 0.1
Summary
Fakultät für Physik, Universität Bielefeld D-33501 Bielefeld, Germany and Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, D-80805 München, Germany (Received 23 November 2020; accepted 9 June 2021; published 9 July 2021). For photon virtualities of Q2 ≳ 20 GeV2, the results of the (hard Pomeron) fit in the tensor-Pomeron model in terms of the variables, Q2, and the virtual-photon-proton energy squared, W2, 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 C2 1⁄4 ε0 ≅ 0.30 for the exponent C2 of the energy-squared dependence in agreement with the results of the fits. For Q2 ≲ 20GeV2, the CDP yields a parameter-free smooth transition from Q2 ≳ 20 GeV2 to Q2 1⁄4 0 photoproduction, in distinction from the tensor-Pomeron model that relies on the additional parameter quantifying the intercept of the soft-Pomeron trajectory
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