Study of deep inelastic inclusive and diffractive scattering with the ZEUS forward plug calorimeter

TL;DR

This study analyzes deep inelastic scattering and diffraction at HERA using the ZEUS detector, revealing complex energy and Q2 dependencies that challenge simple theoretical models and suggest significant perturbative contributions.

Contribution

It provides detailed measurements of diffractive scattering cross sections and structure functions, showing deviations from Regge theory and indicating perturbative QCD effects in diffraction.

Findings

Diffractive cross section rises strongly with energy W, especially at higher Q2.

The ratio of diffractive to total cross section remains constant with W, contradicting Regge predictions.

The diffractive structure function shows Q2 dependence that violates Regge factorization, indicating perturbative effects.

Abstract

Deep inelastic scattering and its diffractive component, ep -> e'gamma*p ->e'XN, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb-1. The measurement covers a wide range in the gamma*p c.m. energy W (37 - 245 GeV), photon virtuality Q2 (2.2 - 80 GeV2) and mass Mx. The diffractive cross section for Mx > 2 GeV rises strongly with W; the rise is steeper with increasing Q2. The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single Pomeron. The ratio of diffractive to total cross section is constant as a function of W, in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to gamma*p scattering. Above Mx of 8 GeV, the ratio is flat with Q2, indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, F2D(3)(beta,xpom,Q2), of the proton. For fixed beta, the Q2 dependence of xpom F2D(3) changes with xpom in violation of Regge factorisation. For fixed xpom, xpom F2D(3) rises as beta -> 0, the rise accelerating with increasing Q2. These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section.