Evidence of strong higher twist effects in diffractive DIS at HERA at moderate Q2

TL;DR

This work tackles higher-twist contributions in diffractive DIS at HERA by performing a twist decomposition of the diffractive structure functions. It demonstrates a significant breakdown of twist-2 DGLAP descriptions at low $Q^2$ and low $\xi$, with data indicating HT scaling like $1/Q^2$ to $1/Q^4$. By applying a twist-decomposed GBW/MMS-Sat saturation framework, including twist-4 and twist-6 components, the authors achieve good agreement with the data, unlike twist-2 alone. The study provides the first strong evidence of higher-twist effects in DIS and motivates further theoretical and experimental exploration of HT phenomena in diffraction and diffractive parton densities.

Abstract

We study a twist decomposition of diffractive structure functions in the diffractive deep inelastic scattering (DDIS) at HERA. At low Q2 and at large energy the data exhibit a strong excess, up to about 100%, above the twist 2 NLO DGLAP description. The excess in consistent with higher twist effects. It is found, that complementing the DGLAP fit by twist 4 and 6 components of the GBW saturation model leads to a good description of data at low Q2. We conclude that the DDIS at HERA provides the first, strong evidence of higher twist effects in DIS.

Figures (2)

• Figure 1: The $\chi^2/\,{\rm d.o.f.}$ for NLO DGLAP and NLO DGLAP + HT fits to ZEUS LRG data ZEUS with $Q^2 < Q^2_{\mathrm{min}}$.
• Figure 2: The LRG ZEUS data for $\xi\sigma_r ^{D(3)}$ at low $Q^2$ compared to a DGLAP fit ZEUS and the DGLAP fit with included twist-4 and twist-4 and 6 corrections from the MMS saturation model. In yellow (gray) --- the region of $\beta$ where the correction due to $q\bar{q} gg$ may be neglected.