Existence of intrinsic charm in the proton

Determine whether the proton contains intrinsic charm, meaning charm-quark parton distributions not generated exclusively by perturbative gluon splitting, and assess whether such a component can produce a charm–anticharm asymmetry.

Background

In the perturbative picture, charm distributions arise through gluon-to-charm–anticharm splitting. Intrinsic charm would instead represent a nonperturbative charm component of the proton and could allow c(x)≠c̄(x). The paper investigates the sensitivity of W-plus-charmed-hadron production ratios to this possibility and finds no significant sensitivity within the studied observables, but the underlying existence of intrinsic charm remains unresolved.

References

Another open question is the existence of intrinsic charm quarks. In the language of PDFs, this would mean that the charm-quark PDFs would not only be generated perturbatively through $g \rightarrow c \Bar{c}$ splittings. Intrinsic charm could manifest another asymmetry, $c\neq \Bar{c}$ .

— Simultaneous production of a $W$ boson and a charmed hadron at the LHC in general-mass variable-flavour-number scheme  (2608.14268 - Alanko et al., 14 Aug 2026) in Section 1, Introduction

Moreover, DIS can be used to answer unresolved questions about PDFs, e.g. whether the proton has an intrinsic charm component.

— Deeply Inelastic Scattering Revisited  (2608.25790 - Hekhorn, 26 Aug 2026) in Section 1.1, “Motivation and non-goals”

Another cause of intrigue is the question of whether the wavefunction of the proton has an intrinsic contribution from the charm quark, which is a long-standing open question, which would be a significant discovery about the fundamental structure of the proton as the charm quark is $\sim 36\%$ more massive than the proton itself. Allowing for intrinsic charm in this formalism is in principle possible, for example based on Ref., but is left for future work.

— Mathematical inverse problem for the world data inference of the parton distribution functions of the proton  (2609.11896 - Hänninen, 10 Sep 2026) in Section 3.5, “Heavy quark production in DIS”