Difference between the and sea quark distributions in the proton was first observed in the violation of the Gottfried sum rule in deep-inelastic scattering (DIS) experiments. The parton momentum fraction x dependence of this difference has been measured over the region 0.02 < x < 0.35 from Drell–Yan and semi-inclusive DIS experiments. The Drell–Yan data suggested a possible sign-change for (x) − (x) near x ~ 0.3, which has not yet been explained by existing theoretical models. We present an independent evidence for the (x) − (x) sign-change at x ~ 0.3 from an analysis of the DIS data. We further discuss the x-dependence of in the context of meson cloud model and the lattice QCD formulation.

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Published in Physics Letters B, v. 736, p. 411-414.

© 2014 The Authors. Published by Elsevier B.V.

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP3.

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This work was supported in part by the National Science Council of the Republic of China and the U.S. Department of Energy under contact Nos. DE-AC02-98CH10886 and DE-FG05-84ER40154, and the National Science Foundation under grant Nos. PHY-0969739 and PHY-1316617.