Intrinsic charm quark valence distribution of the proton

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 of charm quarks and antiquarks in the proton. We propose two novel experimental probes of this intrinsic charm valence component: <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>D</a:mi></a:math>-meson asymmetries in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>Z</c:mi><c:mo>+</c:mo><c:mi>c</c:mi></c:mrow></c:math>-jet production at the LHCb experiment and flavor-tagged structure functions at the Electron-Ion Collider. Published by the American Physical Society 2024