Screening Effects on $F_2$ at Low $x$ and $Q^2$

TL;DR

This paper reviews experimental evidence from HERA indicating the presence of high parton density effects in deep inelastic scattering, highlighting the challenges in understanding quark-gluon systems at small x and Q^2.

Contribution

It synthesizes experimental data and discusses the implications of high parton density phenomena in QCD at HERA, emphasizing the non-perturbative regime.

Findings

Confirmation of high parton density effects at HERA

Evidence of non-perturbative QCD phenomena

Indications of saturation effects in structure functions

Abstract

This is a talk given at Ringberg Workshop:"New Trends in HERA Physics", 30 May - 4 June, 1999.In this talk we discuss how deeply the region of high parton densities has been studied experimentally at HERA. We show that the measurements of deep inelastic structure functions at HERA confirm our theoretical expectation that at HERA we face a challenging problem of understanding a new system of partons: quarks and gluons at short distances with so large densities that we cannot treat this system perturbatively. We collect all experimental indications and manifestations of specific properties of high parton density QCD.