X(3872) as a hybrid state of the charmonium and the hadronic molecule

Understand

In order to understand the structure of the X(3872), the $c \bar c$ charmonium core state coupling to the $D^0 \bar D^{\ast 0}$ and $D^+ D^{\ast -}$ molecular states are studied.

• The strengths of the couplings between the charmonium state and the hadronic molecular states are determined so as to reproduce the observed mass of the the X(3872).
• The isospin symmetry breaking is introduced by the mass differences of the neutral and charged $D$ mesons.
• The obtained structure of the X(3872) is that about 7% is $\ccbar$ charmonium, 75% is the isoscalar $D \bar D^\ast$ molecule and 18% is the isovector $D \bar D^\ast$ molecule, which explains observed properties of the X(3872) well.