The theory of the strong force, quantum chromodynamics, describes the proton in terms of quarks and gluons. The proton is a state of two up quarks and one down quark bound by gluons, but quantum theory predicts that in addition there is an infinite number of quark–antiquark pairs. Both light and heavy quarks, whose mass is respectively smaller or bigger than the mass of the proton, are revealed inside the proton in high-energy collisions. However, it is unclear whether heavy quarks also exist as a part of the proton wavefunction, which is determined by non-perturbative dynamics and accordingly unknown: so-called intrinsic heavy quarks¹. It has been argued for a long time that the proton could have a sizable intrinsic component of the lightest heavy quark, the charm quark. Innumerable efforts to establish intrinsic charm in the proton² have remained inconclusive. Here we provide evidence for intrinsic charm by exploiting a high-precision determination of the quark–gluon content of the nucleon³ based on machine learning and a large experimental dataset. We disentangle the intrinsic charm component from charm–anticharm pairs arising from high-energy radiation⁴. We establish the existence of intrinsic charm at the 3-standard-deviation level, with a momentum distribution in remarkable agreement with model predictions^1,5.We confirm these findings by comparing them to very recent data on Z-boson production with charm jets from the Large Hadron Collider beauty (LHCb) experiment⁶.

强力理论，量子色动力学，用夸克和胶子来描述质子。质子是由胶子束缚的两个上夸克和一个下夸克的状态，但量子理论预测，此外还有无限数量的夸克-反夸克对。质量分别小于或大于质子质量的轻夸克和重夸克都在高能碰撞中暴露在质子内部。然而，尚不清楚重夸克是否也作为质子波函数的一部分存在，这是由非微扰动力学决定的，因此未知：所谓的本征重夸克¹. 长期以来，人们一直认为质子可能具有最轻的重夸克——粲夸克的相当大的内在成分。^在质子2中建立内在魅力的无数努力仍然没有结果。在这里，我们通过基于机器学习和大型实验数据集对核子³的夸克 - 胶子含量的高精度测定来提供内在魅力的证据。我们从高能辐射⁴产生的魅力-反魅力对中分离出内在魅力成分。我们在 3 个标准差水平上确定了内在魅力的存在，其动量分布与模型预测^{1,5非常一致}.我们通过将这些发现与来自大型强子对撞机 (LHCb) 实验^{6的魅力射流的}Z玻色子产生的最新数据进行比较来证实这些发现。