Diffraction Dissociation in Photoproduction at HERA
C. Adloff
TL;DR
The study examines diffraction dissociation in photoproduction at HERA through the process gamma p -> XY with large rapidity gaps, measuring differential cross sections dσ/dM_X^2 at W_gp = 187 and 231 GeV for both proton-elastic and proton-dissociative regimes. By employing a rapidity-gap approach, the analysis connects the MX dependence and energy behavior to a triple-Regge description, and extracts a pomeron intercept of $\alpha_{\text{pom}}(0) = 1.068 \pm 0.016(\text{stat.}) \pm 0.022(\text{syst.}) \pm 0.041(\text{model})$, consistent with hadronic and photoproduction data. For $M_X^2 / W_{gp}^2 < 0.05$, the diffractive contribution is measured as $22.2 \pm 0.6(\text{stat.}) \pm 2.6(\text{syst.}) \pm 1.7(\text{model}) \%$ of the total $\gamma p$ cross section at $W_{gp} = 187$ GeV, confirming substantial diffraction in this regime and extending Regge-based descriptions to high-energy photoproduction. These results unify HERA measurements with fixed-target data and quantify the diffractive component within a coherent triple-Regge framework, contributing to the understanding of soft QCD dynamics in photon-proton interactions.$
Abstract
A study is presented of the process gamma p -->XY, where there is a large rapidity gap between the systems X and Y. Measurements are made of the differential cross section as a function of the invariant mass mx of the system produced at the photon vertex. Results are presented at centre of mass energies of W_gp = 187 GeV and W_gp = 231 GeV, both where the proton dominantly remains intact and, for the first time, where it dissociates. Both the centre of mass energy and the mx^2 dependence of HERA data and those from a fixed target experiment may simultaneously be described in a triple-Regge model. The low mass photon dissociation process is found to be dominated by diffraction, though a sizable subleading contribution is present at larger masses. The pomeron intercept is extracted and found to be alpha_pom(0) = 1.068 \pm 0.016 (stat.) \pm 0.022 (syst.) \pm 0.041 (model), in good agreement with values obtained from total and elastic hadronic and photoproduction cross sections. The diffractive contribution to the process gamma p --> Xp with mx^2 / W_gp^2 < 0.05 is measured to be 22.2 \pm 0.6 (stat.) \pm 2.6 (syst.) \pm 1.7 (model) % of the total gamma p cross section at W_gp = 187 GeV.