Isospin violating decays of positive parity $B_s$ mesons in HM$\chi$PT

Abstract

Recent lattice QCD results suggest that the masses of the first two positive parity $B_s$ mesons lie below the BK threshold, similar to the case of $D^*_{s0}(2317)^+$ and $D_{s1}(2460)^+$ mesons. The mass spectrum of $B_s$ mesons seems to follow pattern of $D_s$ mass spectrum. As in the case of charmed mesons, the structure of positive parity $B_s$ mesons is very intriguing. To shed more light on this issue, we investigate strong isospin violating decays $B_s(0^+) \to B_s^0 \pi^0$, $B_s(1^+) \to B_s^{*0} \pi^0$ and $B_s(1^+) \to B_s^0 \pi \pi$ within heavy meson chiral perturbation theory. The two body decay amplitude arises at the tree level and we show that the loop corrections give significant contributions. On the other hand, in the case of three body decay $B_s(1^+) \to B_s^0 \pi \pi$ amplitude occurs only at the loop level. We find that the decay widths for these decays are: $\Gamma (B_s(1^+) \to B_s^0 \pi \pi)\sim 10^{-3}\,$keV and $\Gamma (B_s(0^+) \to B_s^0 \pi^0) \leq 55\,$keV, $\Gamma (B_s(1^+) \to B_s^{*0} \pi^0) \leq 50\,$keV. More precise knowledge of the coupling constant describing the interaction of positive and negative parity heavy mesons with light pseudoscalar mesons would help to increase accuracy of our calculation.