Valence-quark distributions of pions and kaons in a nuclear medium

Abstract

In-medium valence-quark distributions of π+ and K+ mesons in symmetric nuclear matter are studied by combining the Nambu-Jona-Lasinio model and the quark-meson coupling model. The in-medium properties of the current quarks, which are used as inputs for studying the in-medium pion and kaon properties in the Nambu-Jona-Lasinio model, are calculated within the quark-meson coupling model. The light-quark condensates, light-quark dynamical masses, pion and kaon decay constants, and pion-and kaon-quark coupling constants are found to decrease as nuclear density increases. The obtained valence quark distributions in vacuum for both the π+ and K+ could reasonably describe the available experimental data over a wide range of Bjorken-x. The in-medium valence u-quark distribution in the π+ at Q2=16 GeV2 is found to be almost unchanged compared to the in-vacuum case. However, the in-medium to in-vacuum ratios of both the valence u-quark and valence s-quark distributions of the K+ meson at Q2=16 GeV2 increase with nuclear matter density but show different x-dependence. Namely, the ratio for the valence u-quark distribution increases with x, while that for the valence s quark decreases with x. These features are enhanced at higher density regions.