Near Mass Degeneracy in the Scalar Meson Sector: Implications for $B^*_{(s)0}$ and $B'_{(s)1}$ Mesons

Understand

The empirical observation of near degeneracy of scalar mesons above 1 GeV, namely, the mass of the strange-flavor scalar meson is similar to that of the non-strange one, is at variance with the naive expectation of the quark model.

• Qualitatively, the approximate mass degeneracy can be understood as a consequence of self-energy effects due to strong coupled channels which will push down the mass of the heavy scalar meson in the strange sector more than that in the non-strange partner.
• However, it works in the conventional model without heavy quark expansion, but not in the approach of heavy meson chiral perturbation theory as mass degeneracy and the physical masses of $D_{s0}^*$ and $D_0^*$ cannot be accounted for simultaneously.
• In the heavy quark limit, near mass degeneracy observed in the scalar charm sector will imply the same phenomenon in the $B$ system.