Partners of the X(3872) and heavy quark spin symmetry breaking

Abstract

Since the discovery of the X(3872) the study of heavy meson molecules has been the subject of many investigations. Different experiments have looked for its spin partners and the bottom analogs. On the theoretical side different approaches have been used to understand this state. Some of them as Effective Field Theories (EFT) that impose Heavy Quark Spin Symmetry (HQSS) and so they make predictions for the partners of the X(3872), suggesting the existence of a JPC = 2++ partner in the charm sector or JPC = 1++ or 2++ analogs in the bottom sector.In this work, in order to understand the X(3872), we use a Chiral Quark Model in which, due to the proximity to the DD* threshold, we include cc¯ states coupled to meson-antimeson DD* molecular components. In this coupled channel model the relative position of the bare cc¯ states with two meson thresholds are very important. We have looked for the X(3872) partners and we do not find a bound state in the D* D* JPC = 2++. In the bottom sector we find the opposite situation where the B* B* with JPC = 2++ is bounded while the JPC = 1++ is not. These results show how the coupling with cc¯ states can induce different results than those expected by HQSS. The reason is that this symmetry is worse in the open heavy meson sector than in the hidden heavy meson sector.