$\Lambda(1670)$ production in the $\psi(3686) \to \Lambda \bar \Lambda \eta$ reaction

Abstract

We perform a calculation of the invariant mass distributions in the $\psi(3686) \to \Lambda \bar \Lambda \eta$ reaction, where a neat peak for the excitation of the $\Lambda(1670)$ and $\bar \Lambda(1670)$ in the $\eta \Lambda$ and $\eta \bar \Lambda$ mass distributions, respectively, is observed. Our approach uses the fact that the $\psi(3686)$, a $c \bar c$ state, is a singlet of SU(3) in the $u,d,s$ quarks and constructs the two flavor structures allowed with a pseudoscalar meson, a baryon and an antibaryon. The resonance peaks come from the final state interaction of meson baryon pairs, which generate the $ \Lambda(1670)$ in our approach. With a reasonable relative weight of the two flavor structures, the only free parameter of the theory, we are able to get the three mass distributions in good agreement with experiment, giving extra support to the molecular structure of the $ \Lambda(1670)$ resonance. The agreement with data improves with an extra resonant contribution with mass around 2200 MeV, possibly accounting for some resonances.