New Limits on Intrinsic Charm in the Nucleon from Global Analysis of Parton Distributions

摘要

We present a new global QCD analysis of parton distribution functions, allowing for possible intrinsic charm (IC) contributions in the nucleon inspired by light-front models. The analysis makes use of the full range of available high-energy scattering data for Q~2 approx＞ 1 GeV~2 and W~2 approx＞ 3.5 GeV~2, including fixed-target proton and deuteron cross sections at lower energies that were excluded in previous global analyses. The expanded data set places more stringent constraints on the momentum carried by IC, with _(IC) at most 0.5% (corresponding to an IC normalization of ～1%) at the 4σ level for ΔX~2 = 1. We also critically assess the impact of older EMC measurements of F_2~c at large x, which favor a nonzero IC, but with very large X~2 values.