The magnetic moment of Zc(3900) as an axial-vector molecular state

In this paper, we tentatively assign Zc(3900) to be an axialvector molecular state, and calculate its magnetic moment using the QCD sum rule method in an external weak electromagnetic field. Starting with the two-point correlation function in the external electromagnetic field and expanding it in powers of the electromagnetic interaction Hamiltonian, we extract the mass and pole residue of the Zc(3900) state from the leading term in the expansion and the magnetic moment from the linear response to the external electromagnetic field. The numerical values are mZc=3.97 +/- 0.12GeV in agreement with the experimental value mZcexp=3899.0 +/- 3.6 +/- 4.9MeV, lambda Zc=2.1 +/- 0.4x10-2GeV5 and mu Zc=0.19-0.01+0.04mu N.