Mass spectra of Zc and Zb exotic states as hadron molecules

TL;DR

This paper uses QCD sum rules to calculate the mass spectra of charmonium-like and bottomonium-like molecular states, supporting their interpretation as hadronic molecules for observed exotic Zc and Zb states.

Contribution

It systematically constructs molecular interpolating currents and computes mass spectra, providing theoretical support for the molecular nature of Zc and Zb exotic states.

Findings

Masses of charmonium-like states match observed Zc resonances.

Bottomonium-like state masses support Zb(10610) as a molecular state.

Supports hadronic molecule interpretation of exotic states.

Abstract

We construct charmonium-like and bottomonium-like molecular interpolating currents with quantum numbers J(PC)=1(+-) in a systematic way, including both color singlet-singlet and color octet-octet structures. Using these interpolating currents, we calculate two-point correlation functions and perform QCD sum rule analyses to obtain mass spectra of the charmonium-like and bottomonium-like molecular states. Masses of the charmonium-like q_bar c c_bar q molecular states for these various currents are extracted in the range 3.85-4.22 GeV, which are in good agreement with observed masses of the Zc resonances. Our numerical results suggest a possible landscape of hadronic molecule interpretations of the newly-observed Zc states. Mass spectra of the bottomonium-like q_bar b b_bar q molecular states are similarly obtained in the range 9.92-10.48 GeV, which support the interpretation of the Zb(10610) meson as a molecular state within theoretical uncertainties. Possible decay channels of these molecular states are also discussed.