In experiments exotic meson resonance $T_{ c\bar c}(4020)$ lies above the $D^{ *}\bar{ D}^{ *}$ threshold, and in principle one can not explain $T_{ c\bar c}(4020)$ as a meson-meson bound state because meson-meson bound state must lie below the $D^{ *}\bar{ D}^{ *}$ threshold. In this work, exotic resonance $T_{ c\bar c}(4020)$ is considered as an unstable meson-meson molecular state $D^{ *}\bar{ D}^{ *}$, and the developed Bethe-Salpeter theory for dealing with unstable state is applied to investigate resonance $T_{ c\bar c}(4020)$. We calculate the mass and width of unstable meson-meson molecular state $D^{ *}\bar{ D}^{ *}$ in the framework of relativistic quantum field theory and find that this unstable meson-meson molecular state lies above the $D^{ *}\bar{ D}^{ *}$ threshold, which is consistent with experimental values of resonance $T_{ c\bar c}(4020)$.
Categories: hep-ph