Forward jets and large rapidity gaps

TL;DR

This paper presents measurements of forward jets and rapidity gaps at the LHC, probing QCD in challenging configurations, revealing deviations from common theoretical models in azimuthal de-correlations and jet radiation patterns.

Contribution

It provides experimental data on jet correlations and rapidity gaps that test and challenge existing QCD models in extreme phase-space regions.

Findings

Deviations observed in azimuthal angle de-correlations from theoretical predictions.

Radiation modeling between forward and backward jets is complex and may require new approaches.

Rare events with large rapidity separation and no additional radiation are studied.

Abstract

Hadronic jets are extremely abundant at the LHC, and testing QCD in various corners of phase-space is important to understand backgrounds and some specific signatures of new physics. In this article, various measurements aiming at probing QCD in configurations where the theory modeling become challenging are presented. Azimuthal angle de-correlations are sensitive to hard as well as soft QCD emission, and in most of the events jets are produced in a back-to-back configuration. Events where jets have a large rapidity separation are also rare, and those without additional radiation between the jets are exponentially suppressed. The modeling of radiation between very forward and backward jets is complicated, and may require theoretical tools different with respect to those normally used for central, high-pt events. Observables can be created that are sensitive to all these effects, like the study of azimuthal angle de-correlations between events where the two leading jets have large rapidity separations. The two general-purpose detectors of the LHC have measured these observables, and for some of them interesting deviations with respect to the most commonly used theoretical models are observed.