Evidence for breakdown of the DGLAP description in diffractive DIS at HERA

HERA data on diffractive DIS show deviations from twist 2 DGLAP predictions below $Q^2sim 5$ GeV$^2$ at low pomeron $xi$, which may reach up to 100%. These deviations are consistent with higher twists effects extracted from the saturation model. It is a first direct evidence for the higher twists in DIS. This finding affects determination of the diffractive parton densities that are used for the predictions at the LHC.

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

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.