Abstract
We address a long standing problem concerning the scale behaviour of parton densities in the low x, low Q^2 domain. We emphasize the important role of absorptive corrections at low x and use knowledge of diffractive deep inelastic scattering to exclude the absorptive effect from conventional deep inelastic data. In this way we obtain a significantly different low x behaviour of the gluon density, which is now much better described by linear DGLAP evolution. Accounting also for a second power correction, which arises from the freezing of alpha _s at low Q^2, leads to an essentially flat behaviour of the low x gluon density.
Highlights
The conventional DGLAP evolution does not describe the deep inelastic scattering data in the low x, low Q2 region very well
We explore the effect of absorption by modifying the HERA Deep Inelastic Scattering (DIS) data by subtracting the lowest absorptive contribution using the known MRW results for dDIS parton distribution function (PDF) which had been obtained from their NLO analysis of the H1 diffractive DIS data for Q2 >8.5 GeV2 [28]
We have investigated the effects of absorption, which has the form of a power correction, at the beginning of low Q2 evolution
Summary
The conventional DGLAP evolution does not describe the deep inelastic scattering data in the low x, low Q2 region very well. All possible 2 → 1 ladder recombinations are resummed to leading order of the parameter αsln(1/x)ln(Q2/Q20) It leads to saturation of the gluon density at low Q2 with decreasing x. To investigate the role of the absorptive effects on the behaviour of the gluon in the low x region, we first correct the low x Deep Inelastic Scattering (DIS) data using the known diffractive DIS (dDIS) PDFs [14,15] and the AGK cutting rules [16,17]. The absorptive effect behaves as a 1/Q2 correction (see, for example, Eq (2)) which becomes important due to the large gluon density at low x. Since confinement excludes an interaction at large distances, larger than the finite size of hadrons, it is impossible to reach a low value of the factorization scale
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