  To study a possible role of the quantum chromodynamics (QCD) vacuum in
nuclear and hadron physics, we evaluate a physical quantity in a candidate of
the QCD vacuum. In this study we adopt the Copenhagen (spaghetti) picture of
the QCD vacuum and calculate the ground-state baryon masses in a constituent
quark model. We find that the calculated baryon mass does depend on a parameter
that characterizes the Copenhagen picture of the QCD vacuum and satisfies the
Gell-Mann-Okubo mass relation for the baryon octet. We also observe that the
effective constituent quark mass defined in this study contains a contribution
attributed to the Copenhagen vacuum, that is the gluon background field. We
then estimate the value of the background gluon field as a function of the up
(down) constituent quark mass by using the baryon masses as inputs.
