Masses of scalar and axial-vector B mesons revisited

Abstract

The SU(3) quark model encounters a great challenge in describing even-parity mesons. Specifically, the qbar{q} quark model has difficulties in understanding the light scalar mesons below 1 GeV, scalar and axial-vector charmed mesons and 1^+ charmonium-like state X(3872). A common wisdom for the resolution of these difficulties lies on the coupled channel effects which will distort the quark model calculations. In this work, we focus on the near mass degeneracy of scalar charmed mesons, D_{s0}^* and D_0^{*0}, and its implications. Within the framework of heavy meson chiral perturbation theory, we show that near degeneracy can be qualitatively understood as a consequence of self-energy effects due to strong coupled channels. Quantitatively, the closeness of D_{s0}^* and D_0^{*0} masses can be implemented by adjusting two relevant strong couplings and the renormalization scale appearing in the loop diagram. Then this in turn implies the mass similarity of B_{s0}^* and B_0^{*0} mesons. The P_0^* P'_1 interaction with the Goldstone boson is crucial for understanding the phenomenon of near degeneracy. Based on heavy quark symmetry in conjunction with corrections from QCD and 1/m_Q effects, we obtain the masses of B^*_{(s)0} and B'_{(s)1} mesons, for example, M_{B_{s0}^*}= (5715pm 1),mathrm{MeV}+delta Delta _S, M_{B'_{s1}}=(5763pm 1),mathrm{MeV}+delta Delta _S with delta Delta _S being 1/m_Q corrections. We find that the predicted mass difference of 48 MeV between B'_{s1} and B_{s0}^* is larger than that of 20–30 MeV inferred from the relativistic quark models, whereas the difference of 15 MeV between the central values of M_{B'_{s1}} and M_{B'_1} is much smaller than the quark model expectation of 60–100 MeV. Experimentally, it is important to have a precise mass measurement of D_0^* mesons, especially the neutral one, to see if the non-strange scalar charmed meson is heavier than the strange partner as suggested by the recent LHCb measurement of the D_0^{*pm }.