The intrinsic charm quark valence distribution of the proton

TL;DR

This paper provides evidence that the proton's wave function contains an intrinsic charm valence component, which cannot be explained by perturbative processes, supported by new determinations of charm PDFs and proposed experimental tests.

Contribution

It offers the first quantitative indication of an intrinsic charm valence distribution in the proton, using novel PDF determinations and proposing new experimental probes.

Findings

Evidence for a nonvanishing intrinsic charm valence component.

Charm PDFs show asymmetry between charm quarks and antiquarks.

Proposed experimental tests at LHCb and Electron-Ion Collider.

Abstract

We provide a first quantitative indication that the wave function of the proton contains unequal distributions of charm quarks and antiquarks, i.e. a nonvanishing intrinsic valence charm distribution. A significant nonvanishing valence component cannot be perturbatively generated, hence our results reinforce previous evidence that the proton contains an intrinsic (i.e., not radiatively generated) charm quark component. We establish our result through a determination of the parton distribution functions (PDFs) of charm quarks and antiquarks in the proton. We propose two novel experimental probes of this intrinsic charm valence component: D-meson asymmetries in Z+c-jet production at the LHCb experiment, and flavor-tagged structure functions at the Electron-Ion Collider.