Diffractive Dijet Photoproduction in ep Collisions at HERA

TL;DR

This paper reports measurements of diffractive dijet photoproduction cross sections in ep collisions at HERA, comparing experimental data with QCD calculations and Monte Carlo models, revealing a suppression factor and first-time ratio measurements.

Contribution

It provides the first measurements of ratios of diffractive to inclusive dijet cross sections in ep collisions and compares them with Monte Carlo models.

Findings

Measured cross sections are about 0.6 times the NLO QCD predictions.

No significant dependence of suppression factor on photon momentum fraction x_gamma.

First-time measurement of diffractive to inclusive dijet cross section ratios.

Abstract

Measurements are presented of single and double-differential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb^-1. The events are of the type ep -> eXY, where the hadronic system X contains at least two jets and is separated by a large rapidity gap from the system Y, which consists of a leading proton or low-mass proton excitation. The dijet cross sections are compared with QCD calculations at next-to-leading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the next-to-leading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction x_gamma of the photon four-momentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.