Study of Photon Dissociation in Diffractive Photoproduction at HERA

TL;DR

This study measures and analyzes the cross sections and mass spectrum of photon dissociation in diffractive photoproduction at HERA, providing insights into pomeron exchange mechanisms and the structure of diffractive processes.

Contribution

It presents the first detailed measurement of the diffractive dissociation cross section and the mass spectrum, supporting the triple pomeron model and estimating additional PPR contributions.

Findings

The fraction of diffractive dissociation is approximately 6.2% of total photoproduction.

The single diffractive cross section is about 13.3% of the total cross section.

The mass spectrum fits the triple pomeron model with an intercept of 1.12.

Abstract

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W ~ 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is gamma p -> X N, where X is the diffractively dissociated photon system of mass M_X and N is either a proton or a nucleonic system with mass M_N < 2GeV. The cross section for this process in the interval 3 < M_X < 24 GeV relative to the total photoproduction cross section was measured to be sigma^partial_D / sigma_tot = 6.2 +- 0.2(stat) +- 1.4(syst)%. After extrapolating this result to the mass interval of m_phi^2 < M_X^2 < 0.05 W^2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, gamma p -> X p, is found to be sigma_SD / sigma_tot = 13.3 +- 0.5(stat) +- 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M_X < 24 GeV can be described by the triple pomeron (PPP) diagram with an effective pomeron intercept of alpha_P(0) = 1.12 +- 0.04(stat) +- 0.08(syst). The cross section for photon dissociation in the range 3 < M_X < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < M_X < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (PPR) term, its contribution to the diffractive cross section in the interval 3 < M_X < 24 GeV is estimated to be f_PPR = 26 +- 3(stat) +- 12(syst)%.