Two-particle contributions and nonlocal effects in the QCD sum rules for the axial vector tetraquark candidate Zc(3900)

Abstract

In this article, we study the [Formula: see text] with the QCD sum rules in details by including the two-particle scattering state contributions and nonlocal effects between the diquark and antidiquark constituents. The two-particle scattering state contributions cannot saturate the QCD sum rules at the hadron side, the contribution of the [Formula: see text] plays an unsubstitutable role, we can saturate the QCD sum rules with or without the two-particle scattering state contributions. If there exists a repulsive barrier or spatial distance between the diquark and antidiquark constituents, the Feynman diagrams can be divided into the factorizable and nonfactorizable diagrams. The factorizable diagrams consist of two-colored clusters and lead to a stable tetraquark state. The nonfactorizable Feynman diagrams correspond to the tunneling effects, which play a minor important role in the QCD sum rules, and are consistent with the small width of the [Formula: see text]. It is feasible to apply the QCD sum rules to study the tetraquark states, which begin to receive contributions at the order [Formula: see text], not at the order [Formula: see text].