Dijet Cross Sections and Parton Densities in Diffractive DIS at HERA

TL;DR

This study measures diffractive dijet cross sections in deep-inelastic scattering at HERA and confronts them with next-to-leading order QCD predictions based on diffractive parton distribution functions (DPDFs) extracted from inclusive diffractive data. It confirms QCD factorisation in the tested kinematic domain and performs a combined NLO QCD fit to inclusive and dijet data, yielding the H1 2007 Jets DPDF with well-constrained quark and gluon diffractive densities across 0.05 < z_{I\!P} < 0.9, notably improving the high-z_{I\!P} gluon density. The results demonstrate that dijet data provide direct sensitivity to the diffractive gluon density and offer a more precise picture of diffraction relevant for LHC phenomenology. Overall, the work strengthens the use of diffractive PDFs for predicting hard diffractive processes and showcases the compatibility of H1 measurements with factorised QCD evolution.

Abstract

Differential dijet cross sections in diffractive deep-inelastic scattering are measured with the H1 detector at HERA using an integrated luminosity of 51.5 pb-1. The selected events are of the type ep --> eXY, where the system X contains at least two jets and is well separated in rapidity from the low mass proton dissociation system Y. The dijet data are compared with QCD predictions at next-to-leading order based on diffractive parton distribution functions previously extracted from measurements of inclusive diffractive deep-inelastic scattering. The prediction describes the dijet data well at low and intermediate zpom (the fraction of the momentum of the diffractive exchange carried by the parton entering the hard interaction) where the gluon density is well determined from the inclusive diffractive data, supporting QCD factorisation. A new set of diffractive parton distribution functions is obtained through a simultaneous fit to the diffractive inclusive and dijet cross sections. This allows for a precise determination of both the diffractive quark and gluon distributions in the range 0.05<zpom<0.9. In particular, the precision on the gluon density at high momentum fractions is improved compared to previous extractions.

Figures (8)

• Figure 1: Leading order diagram for diffractive dijet production in DIS.
• Figure 2: Cross sections for diffractive dijets, differential in $y$, $\log x_{I\!\!P}$, $p^\star_{T,jet1}$ and $\Delta\eta^{\star}_{jets}$ compared to NLO predictions based on the parton-densities from the H1 2006 DPDF fits h1f2d97. The data are shown as black points with the inner and outer error bars denoting the statistical and quadratically added uncorrelated systematic uncertainties, respectively. The hatched band indicates the correlated systematic uncertainty. The dashed line shows the NLO QCD prediction based on the H1 2006 DPDF fit B, which is surrounded by a dark shaded band indicating the parton density and hadronisation uncertainties. In the light shaded band the scale uncertainty is added quadratically to the parton density and hadronisation uncertainties. The dotted line represents the NLO QCD prediction based on the H1 2006 DPDF fit A.
• Figure 3: Cross section for diffractive dijets, differential in $z_{I\!\!P}$ compared to NLO predictions based on the parton-densities from the H1 2006 DPDF fits h1f2d97. The data are shown as black points with the inner and outer error bars denoting the statistical and quadratically added uncorrelated systematic uncertainties, respectively. The hatched band indicates the correlated systematic uncertainty. In the left panel the data are compared to the NLO QCD prediction based on the H1 2006 DPDF fit A (dotted line) and in the right panerl to the prediction based on the H1 2006 DPDF fit B (dashed line). The lines are surrounded by a dark shaded band indicating the parton density and hadronisation uncertainties. In the light shaded band the scale uncertainty is added quadratically to the parton density and hadronisation uncertainties. The prediction for $z_{I\!\!P}>0.9$ is not shown since the hadronisation corrections for this bin cannot be determined reliably.
• Figure 4: Cross sections for diffractive dijets restricted to $z_{I\!\!P}<0.4$, differential in $y$, $\log x_{I\!\!P}$, $p^\star_{T,jet1}$ and $\Delta\eta^{\star}_{jets}$ compared to NLO predictions based on the parton-densities from the H1 2006 DPDF fits h1f2d97. The data are shown as black points with the inner and outer error bars denoting the statistical and quadratically added uncorrelated systematic uncertainties, respectively. The hatched band indicates the correlated systematic uncertainty. The dashed line shows the NLO QCD prediction based on the H1 2006 DPDF fit B, which is surrounded by a dark shaded band indicating the parton density and hadronisation uncertainties. In the light shaded band the scale uncertainty is added quadratically to the parton density and hadronisation uncertainties. The dotted line represents the NLO QCD prediction based on the H1 2006 DPDF fit A.
• Figure 5: Cross section for diffractive dijet production doubly differential in $z_{I\!\!P}$ and the scale $Q^2+p_{T,jet1}^{\star 2}$. The data are shown as black points with the inner and outer error bars denoting the statistical and quadratically added uncorrelated systematic uncertainties, respectively. The hatched band indicates the correlated systematic uncertainty. The solid line shows the NLO QCD prediction based on the H1 2007 Jets DPDF. Data points in the highest $z_{I\!\!P}$ bin were not included in the fit since the hadronisation corrections cannot be evaluated reliably.