Dissociation Of Virtual Photons Research Articles

Deep inelastic scattering with leading protons or large rapidity gaps at HERA

The dissociation of virtual photons, γ ⋆ p → X p , in events with a large rapidity gap between X and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities Q 2 > 2 GeV 2 and γ ⋆ p centre-of-mass energies 40 < W < 240 GeV , with M X > 2 GeV , where M X is the mass of the hadronic final state, X. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex and Φ, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of Q 2 and x P , the fraction of the proton's momentum carried by the diffractive exchange, as well as β, the Bjorken variable defined with respect to the diffractive exchange.

ZEUS results on inclusive diffraction

Inclusive diffractive dissociation of virtual photons, γ ∗ p → X p , has been studied in ep interactions with the ZEUS detector at HERA. The measurements are interpreted in the framework of QCD-motivated models and the results of a next-to-leading-order QCD fit to the high Q 2 data are reviewed.

Inclusive diffraction in ep collisions

The diffractive dissociation of virtual photons, γ∗ p → Xp, has been studied in ep interactions at HERA with the H1 and ZEUS detectors. The data are presented in terms of the diffractive structure function F2D. The t and the φ dependences of the cross section are measured. A new NLO DGLAP QCD fit is performed to the H1 data. The resulting parton densities are used to predict diffractive dijet and charm cross sections at HERA and the Tevatron, as a test of factorization in hard diffraction.

Thrust jet analysis of deep-inelastic large-rapidity-gap events

A thrust analysis of Large-Rapidity-Gap events in deep-inelastic $ep$ collisions is presented, using data taken with the H1 detector at HERA in 1994. The average thrust of the final states $X$ , which emerge from the dissociation of virtual photons in the range $10 < Q^2 < 100 {\rm GeV}^2$ , grows with hadronic mass $M_X$ and implies a dominant 2-jet topology. Thrust is found to decrease with growing $P_t$ , the thrust jet momentum transverse to the photon-proton collision axis. Distributions of $P_t^2$ are consistent with being independent of $M_X$ . They show a strong alignment of the thrust axis with the photon-proton collision axis, and have a large high $-P_t$ tail. The correlation of thrust with $M_X$ is similar to that in $e^+e^-$ annihilation at $\sqrt s_{ee}=M_X$ , but with lower values of thrust in the $ep$ data. The data cannot be described by interpreting the dissociated system $X$ as a $q\bar q$ state but inclusion of a substantial fraction of $q\bar q g$ parton configurations leads naturally to the observed properties. The soft colour exchange interaction model does not describe the data.