Diffractive DIS Research Articles

QCD analysis of diffractive and leading-proton DIS structure functions in the framework of fracture functions

We present a combined QCD analysis of recent data produced by the H1 and ZEUS collaborations on the diffractive and leading-proton deep inelastic positron--proton scattering structure functions, $F_2^{D(3)}$ and $F_2^{LP(3)}$, respectively. It is shown that the QCD framework for semi-inclusive processes, based on fracture functions, allows a unified treatment of both diffractive and leading-proton processes, and offers a precise perturbative QCD description for them, alternative to those that rely on model-dependent assumptions, such as Regge factorization, or other non-perturbative approaches

Twist-4 effects and Q2 dependence of diffractive DIS

In this letter we report the direct perturbative QCD evaluation of twist-4 effects in diffractive DIS. They are large and have a strong impact on the Q 2 dependence of diffractive structure functions at large β. Based on the AGK rules, we comment on the possible contribution from diffractive higher twists to ∝ 1 Q 2 corrections to proton structure function at small x. These corrections to the longitudinal structure function F L may be particularly large.

Unitarity effects in DIS

We argue that diffractive DIS, dominated by soft interactions, is probably the unique process which allows us to observe unitarity effects in DIS. Guided by a close analogy between the diffractive dissociation of a highly virtual photon and the elastic scattering of hadrons we propose a specific procedure to analyse the data in order to detect the onset of the unitarity limit. Lacking appropriate data, we use the predictions of a realistic model as an input for our analysis, to demonstrate that the output unitarity signal is sufficiently large to be detectable.

A screened BFKL interpretation of F2 in the exceedingly small x limit

In this letter we show that the behaviour of F 2, at very small x B , agrees with the behaviour expected from the BFKL evolution equation, when screening corrections are included. We obtain a description which is consistent with the data, however, we require the screening corrections to be relatively large (about a quarter of the total DIS cross section). The relation between the screening corrections and the diffractive DIS cross section is discussed.

Energy flow in the hadronic final state of diffractive and non-diffractive deep-inelastic scattering at HERA

An investigation of the hadronic final state in diffractive and non-diffractive deep-inelastic electron-proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo-rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep-inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep-inelastic ep scattering, in which a sizeable diffractive contribution is present because of non-perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description. © Springer-Verlag 1996.

Measurement of the diffractive cross section in deep inelastic scattering

Diffractive scattering of $\gamma^* p \to X + N$, where $N$ is either a proton or a nucleonic system with $M_N~<~4$~GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the $\gamma^* p$ c.m. energy $W$ between 60 and 245~GeV and of the mass $M_X$ of the system $X$ up to 15~GeV at average $Q^2$ values of 14 and 31~GeV$^2$. The diffractive cross section $d\sigma^{diff} /dM_X$ is, within errors, found to rise linearly with $W$. Parameterizing the $W$ dependence by the form $d\sigma^{diff}/dM_X \propto (W^2)^{(2\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}} -2)}$ the DIS data yield for the pomeron trajectory $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}} = 1.23 \pm 0.02(stat) \pm 0.04 (syst)$ averaged over $t$ in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}}$ extracted from soft interactions. The value of $\overline{\mbox{$\alpha_{_{I\hspace{-0.2em}P}}$}}$ measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton $F^{D(3)}_2(\beta,Q^2, \mbox{$x_{_{I\hspace{-0.2em}P}}$})$ has been determined, where $\beta$ is the momentum fraction of the struck quark in the pomeron. The form $F^{D(3)}_2 = constant \cdot (1/ \mbox{$x_{_{I\hspace{-0.2em}P}}$})^a$ gives a good fit to the data in all $\beta$ and $Q^2$ intervals with $a = 1.46 \pm 0.04 (stat) \pm

Pomeron physics in diffractive deep inelastic scattering at large

I review recent progress in the perturbative QCD approach to pomeron physics in deep inelastic scattering (DIS) at large 1 x .(refs.1–4). I discuss the crucial role the color transparency plays in a diffractive DIS, and how it can be quantified in terms of the wave function (WF) of (partonic) hadronic fluctuations of photons and universal, flavour independent, q q pair interaction cross section. Different DIS processes probe this universal cross section at different sizes. The emerging WF formalism greatly simplifies the involved calculations. I present quantitative predictions for the nuclear shadowing and the diffraction dissociation (DD) rate in DIS, and the valence and sea quark distributions in a QCD Pomeron. I point out a dramatic difference of sea densities in a nucleon as probed by muons and neutrinos and flavour dependence of the pomeron couplings in DD and conclude that perturbative QCD pomeron does not factorize. I emphasize a numerical importance of shadowing in deuterium for tests of the Gottfried sum rule.