Di-jet Event Rates in Deep-Inelastic Scattering at HERA
C. Adloff
TL;DR
The paper measures di-jet event rates in deep-inelastic scattering at HERA with the H1 detector to test perturbative QCD in the region $10^{-4}\lesssim x_{\mathit{Bj}}\lesssim 10^{-2}$ and $5\,\mathrm{GeV}^2\lesssim Q^2\lesssim 100\,\mathrm{GeV}^2$. It compares data to LO direct-photon QCD, LO with resolved virtual-photon contributions, the colour dipole model, and NLO QCD calculations including direct and resolved photon effects, across three jet-p_t selection schemes. The results show that direct (point-like) LO QCD fails to describe the data, whereas models including virtual-photon structure or dipole radiation describe the measurements well; NLO DIR with PSP+RES further improves the description, particularly at low $Q^2$, though scale choices and photon structure uncertainties remain significant. These findings provide evidence for a non-negligible virtual-photon structure and for non-ordered gluon radiation in ep collisions, with implications for jet production modeling and photon-parton dynamics at HERA.
Abstract
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain ~5 < Q^2 < ~100 GeV^2 and ~10^(-4) < x_Bj < ~10^(-2), and for jet transverse momenta squared p_t^2 > ~Q^2. The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb^(-1). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of Q^2 and x_Bj. Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.