The Color Dipole Picture of low-x DIS: Model-Independent and Model-Dependent Results

الأصل · EN

We present a detailed examination of the color-dipole picture (CDP) of low-x deep inelastic scattering. We discriminate model-independent results, not depending on a specific parameterization of the dipole cross section, from model-dependent ones. The model-independent results include the ratio of the longitudinal to the transverse photoabsorption cross section at large Q², or equivalently the ratio of the longitudinal to the unpolarized proton structure function, Fₗ (x,Q²)=0.27 F₂ (x, Q²), as well as the low-x scaling behavior of the total photoabsorption cross section σᵧ*ₚ (W², Q²)=σᵧ*ₚ (η(W², Q²)) as (1 / η(W², Q²)) for η(W², Q²) <1, and as 1/η(W², Q²) for η(W², Q²) ≫ 1. Here, η(W², Q²) denotes the low-x scaling variable, η(W², Q²)=(Q² + m²₀) / Λ²sat (W²) with Λ²sat (W²) being the saturation scale. The model-independent analysis also implies W²→∞, Q² fixed σᵧ*ₚ (W², Q²) / σᵧₚ (W²) → 1 at any Q² for asymptotically large energy, W. Consistency with pQCD evolution determines the underlying gluon distribution and the numerical value of C₂ = 0.29 in the expression for the saturation scale, Λ² (W²) (W²)ᶜ². In the model-dependent analysis, by restricting the mass of the actively contributing q q fluctuations by an energy-dependent upper bound, we extend the validity of the color-dipole picture to x Q² / W² ≤ 0.1. The theoretical results agree with the world data on DIS for 0.036 GeV² ≤ Q² ≤ 316 GeV².