On the Interpretation of the NA51 Experiment
  We study the $p-n$ Drell-Yan asymmetry, recently measured by the NA51 collaboration, and conclude that the value quoted by their experiment only sets a lower limit on the asymmetry of the proton sea. In particular, we notice that charge symmetry breaking between the proton and the neutron may produce corrections which should be taken into account. 
F. M. Steffens and A. W. Thomas (Univ. of Adelaide)