Speaker
Description
The standard model provides for the existence of hybrid states that contain a gluon in addition to the quark and the antiquark. The $\pi_1(1600)$ and the recently observed $\eta_1(1855)$ are examples of such exotic mesons. In the present work, we study the masses and the two-body decays of the members of the lightest hybrid nonet with quantum numbers $1^{-+}$ using a Lagrangian invariant under the $SU(3)$ flavor symmetry, parity and charge conjugation. We perform a statistical fit to the available experimental and lattice data on the two-body decays of the $\pi_1(1600)$ to arrive at the corresponding coupling constants. Using the parameters so obtained, we analyze the possible decay channels for the hybrid kaons and the isoscalars. We find that the hybrid kaons have to be at least as broad as the $\pi_1(1600)$. The two isoscalar states are the result of a weak mixing between the strange and non-strange isoscalar states. The heavy isoscalar can be identified with the recently observed $\eta_1(1855)$. This state is expected to decay mostly into axial kaons ($K_1(1270)K$). The light isoscalar is expected to be marginally lighter than the $\pi_1(1600)$, and significantly narrower than its heavier sibling.
