Article

Dijet production in diffractive deep inelastic scattering at HERA

DOI: 10.3360/dis.2007.112
Source: OAI

ABSTRACT The production of dijets in diffractive deep inelastic scattering has been
measured with the ZEUS detector at HERA using an integrated luminosity of $61
\pbi$. The dijet cross section has been measured for virtualities of the
exchanged virtual photon, $5 < Q^2 < 100 \gev^2$, and $\gamma^{*} p$
centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the
inclusive k_{T} algorithm in the $\gamma^* p$ frame, were required to have a
transverse energy $E^*_{T, \rm jet} > 4 \gev$ and the jet with the highest
transverse energy was required to have $E^*_{T,\rm jet} > 5 \gev$. All jets
were required to be in the pseudorapidity range $-3.5 < \eta^*_{\rm jet} < 0$.
The differential cross sections are compared to leading-order predictions and
next-to-leading-order QCD calculations based on recent diffractive parton
densities extracted from inclusive diffractive deep inelastic scattering data.

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    ABSTRACT: The H1 and Zeus collaborations have measured the dijet and inclusive diffractive DIS cross sec- tions. Diffractive parton density functions (DPDFs) have been extracted from NLO QCD fits to the inclusive data and the predictions of these DPDFs compare well with measurements of diffrac- tive dijets in DIS, proving the validity of the factorisatio n approximations used in their extraction. The inclusive and dijet data are then used in a combined fit to c onstrain the diffractive singlet and gluon with good precision over the full phase space. The measurement of the diffractive longitu- dinal structure function agrees well with the predictions b ased on NLO QCD fits to the inclusive data. The predictions of DPDFs are compared to diffractive dijets in photoproduction where the issue of survival probability in a hadron-hadron environment can be studied. While these studies at HERA remain inconclusive for the time being, exclusive measurements made at the Tevatron bolster confidence in calculations for survival probabilit ies at hadron-hadron machines. Exclusive diffractive vector meson production and deeply virtual Compton scattering have also been stud- ied at HERA; the results compare reasonably well with the expectations of QCD and in particular with GPD models. Finally, measurements of the double parton scattering cross-section show that this will need to be understood as a background to rare processes.

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