New limits on intrinsic charm in the nucleon from global analysis of   parton distributions
  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 > 1 GeV^2 and W^2 > 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 <x>_IC at most 0.5% (corresponding to an IC normalization of ~ 1%) at the 4-sigma level for Delta chi^2 = 1. We also critically assess the impact of older EMC measurements of F_2c at large x, which favor a nonzero IC, but with very large chi^2 values. 
P. Jimenez-Delgado, T. J. Hobbs, J. T. Londergan, W. Melnitchouk
hep-ph hep-ex nucl-th