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Register a new userEvidence for breakdown of the DGLAP description in diffractive DIS at HERA
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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.
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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.
We calculate the cross section of diffractive dijet photoproduction in $ep$ scattering at next-to-leading order (NLO) of perturbative QCD (pQCD), which we supplement by a model of factorization breaking for the resolved-photon contribution. In this model, the suppression depends on the flavor and momentum fraction of the partons in the photon. We show that within experimental and theoretical uncertainties, the resulting approach provides a good description of the available HERA data in most of the bins. Hence, taken together with the observation that NLO pQCD explains well the data on diffractive photoproduction of open charm in $ep$ scattering, our model of factorization breaking presents a viable alternative to the scheme based on the global suppression factor.
We calculate the diffraction slope $B_{D}$ for diffractive DIS. We find a counterintuitive rise of $B_{D}$ from exclusive diffractive excitation of vector mesons to excitation of continuum states with $M^{2} sim Q^{2}$. For the small-mass continuum we predict a rapid variation of $B_{D}$ with $M^{2}$ on the scale $m_{V}^{2}$ and a sharp drop of $B_{D}$ for a small-mass continuum above the vector meson excitation.
We present a NLO calculation of prompt photon production in DIS. The calculation involves direct, fragmentation and resolved contributions. It is performed in the virtual-photon proton center-of-mass system. A comparison of the theoretical results with HERA data is carried out.
We present a global analysis of available data on inclusive structure functions measured in electron-proton scattering at small values of Bjorken-x, including the latest data from the combined HERA analysis on reduced cross sections. Our approach relies on the dipole formulation of DIS together with the use of the non-linear running coupling BK equation for the description of the small-x dynamics. With the resulting parametrization we are able to describe the latest FL data measured by the H1 collaboration. Further, we discuss the kinematical domain where significant deviations from NLO-DGLAP should be expected and the ability of non-linnear physics to account for such deviations.
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