Precision determination of the small-$x$ gluon from charm production at LHCb

TL;DR

This paper uses LHCb forward charm production data at multiple energies to precisely determine the small-$x$ gluon distribution, significantly reducing uncertainties in this region relevant for various high-energy physics applications.

Contribution

It introduces a novel method of incorporating normalized distributions and cross-section ratios from LHCb data into PDF fits to constrain the small-$x$ gluon more accurately.

Findings

Reduces gluon PDF uncertainties by up to an order of magnitude at $x\simeq 10^{-6}$

Demonstrates the effectiveness of forward charm data in constraining small-$x$ gluons

Implications for collider physics, cosmic rays, and neutrino studies.

Abstract

The small-$x$ gluon in global fits of parton distributions is affected by large uncertainties from the lack of direct experimental constraints. In this work we provide a precision determination of the small-$x$ gluon from the exploitation of forward charm production data provided by LHCb for three different centre-of-mass (CoM) energies: 5~TeV, 7~TeV and 13~TeV. The LHCb measurements are included in the PDF fit by means of normalized distributions and cross-section ratios between data taken at different CoM values, $R_{13/7}$ and $R_{13/5}$. We demonstrate that forward charm production leads to a reduction of the PDF uncertainties of the gluon down to $x\simeq 10^{-6}$ by up to an order of magnitude, with implications for high-energy colliders, cosmic ray physics and neutrino astronomy.