Molecular Structure Effects in Low-Lying $P$-wave Bottom-Strange Meson Spectrum

Abstract

Recently, the LHCb Collaboration reported a new narrow bottom-strange meson, $B_{s0}^*(5700)$ with mass $M= (5698.9 \pm 1.5 \pm 0.6)$~MeV, width $Γ<9.8$~MeV, and spin-parity $J^P=0^+$ in the $B_s^0π^0$ invariant-mass spectrum. Motivated by this observation, we study the low-lying $P$-wave $B_s$ mesons in a two-stage refined constituent quark model. The one-loop radiative corrections to the confinement--one-gluon exchange potential ($α_s^2$) lower the whole multiplet by $25$--$50$~MeV and improve the level ordering; however, the scalar $B_{s0}^*$ mass still exceeds the LHCb data by $\sim120$~MeV in a purely compact picture. The inclusion of the coupled-channel dynamics is decisive: the $BK$ threshold, lying close to the scalar mass, generates a sizeable meson--meson (molecular-like) component that pulls the pole down to $\sim5727$~MeV, within $30$~MeV of the measurement, and simultaneously suppresses the $S$-wave phase space, naturally accounting for the anomalously narrow width. Consistent results are obtained for the $1^+$ $B_{s1}$ partner, for which we predict a mass $\sim5747$--$5755$~MeV, in agreement with the chiral-doubling scenario. The $B_{s1}$ state is expected to be very narrow and decaying mainly through the isospin-violating $B_s^*π^0$ and radiative $B_sγ$, $B_s^*γ$ modes, providing a clear discovery target at LHC Run~3. The $E1$ radiative widths of the $j_\ell=1/2$ states are predicted at the $50\sim 60$~keV, and the strong width of the pure $j_\ell=3/2$ state $B_{s2}^*(5840)$ ($1.5$~MeV) reproduces the measurement. Our results support the interpretation of $B_{s0}^*(5700)$ as a near-threshold scalar with strong molecular dressing and establish the predicted $1^+$ $B_{s1}(5747)$ as the decisive test of the hadronic dynamics in the $B_s$ sector.