Diffraction and correlations at the LHC: definitions and observables

TL;DR

This paper examines how different definitions of diffractive events at the LHC impact the interpretation of experimental data, emphasizing the importance of careful analysis to distinguish genuine Pomeron effects from fluctuations.

Contribution

It compares unitarity-based and LRG-based definitions of diffraction, quantifies fluctuation effects, and links long-range correlations to multi-Pomeron diagrams.

Findings

LRG can result from fluctuations, complicating Pomeron extraction.

Long-range correlations can originate from multi-Pomeron interactions.

Early LHC data can clarify the nature of soft interactions.

Abstract

We note that the definition of diffractive events is a matter of convention. We discuss two possible `definitions': one based on unitarity and the other on Large Rapidity Gaps (LRG) or Pomeron exchange. LRG can also arise from fluctuations and we quantify this effect and some of the related uncertainties. We find care must be taken in extracting the Pomeron contribution from LRG events. We show that long-range correlations in multiplicities can arise from the same multi-Pomeron diagrams that are responsible for LRG events, and explain how early LHC data can illuminate our understanding of `soft' interactions.