# The small-x gluon from forward charm production: implications for a 100 TeV proton collider

## TL;DR

This paper reviews how forward charm production data from LHCb constrains small-x gluon PDFs, impacting predictions for ultra-high energy astrophysics and future colliders like the FCC, by reducing uncertainties in key cross-sections.

## Contribution

It introduces a method to improve small-x gluon PDF constraints using LHCb forward charm data and explores implications for 100 TeV collider physics and astrophysics.

## Key findings

- LHCb data constrains small-x gluon PDFs effectively.
- Improved PDFs reduce uncertainties in high-energy cross-section predictions.
- Electroweak scale processes at FCC are sensitive to small-x gluon behavior.

## Abstract

We review the constraints on the small-x gluon PDF that can be derived by exploiting the forward D meson production data from the LHCb experiment at $\sqrt{s}=5,7$ and 13 TeV. We then discuss the phenomenological implications of the resulting improved small-x gluon for ultra-high energy astrophysics, in particular neutrino telescopes, as well as for the proposed Future Circular Collider (FCC) with $\sqrt{s}=100$ TeV. We illustrate how at the FCC even electroweak scale cross-sections can become sensitive to the small-x region of the quark and gluon PDFs, and then demonstrate how the addition of the LHCb heavy meson production measurements leads to a reduction of PDF uncertainties for various benchmark cross-sections.