Forward Physics with Rapidity Gaps at the LHC

TL;DR

Soft diffractive processes at the LHC remain uncertain and challenge reliable soft-QCD modeling, with the gap-survival factor $\hat{S}^2$ playing a central role. The authors propose forward shower counters (FSC) around CMS to tag rapidity gaps and enable measurements of $\sigma_{SD}$(low $M$) and central diffractive production $d\sigma/d\eta_1 d\eta_2$, operating at low luminosity to suppress pile-up. They present FSC layout, simulated performance across $60\mathrm{m}<|z|<140\mathrm{m}$, and level-1 trigger configurations for various gap/particle patterns, demonstrating efficiency for diffractive channels. This approach could enable the LHC to function as a gluon-gluon collider in the color-singlet channel and provide crucial data to constrain non-perturbative QCD, with implications for Higgs studies and potential new physics in diffractive channels.

Abstract

A rapidity gap program with great potential can be realized at the Large Hadron Collider, LHC, by adding a few simple forward shower counters (FSCs) along the beam line on both sides of the main central detectors, such as CMS. Measurements of single diffractive cross sections down to the lowest masses can be made with an efficient level-1 trigger. Exceptionally, the detectors also make feasible the study of Central Diffractive Excitation, and in particular the reaction g + g to g + g, in the color singlet channel, effectively using the LHC as a gluon-gluon collider.

Figures (2)

• Figure 1: The proposed layout of the FSC counters on both sides of the CMS intersection region from $z = \pm$60m to $z = \pm$ 140m. The vertical lines indicate the locations of the proposed counters.
• Figure 2: Region between the MBXW magnets where the FSC counters can be installed. (Photograph taken before the connecting pipe was installed; it shows accessible elliptical beam pipe regions.)