The LHCb state $P_{\psi s}^{\Lambda }(4338)$ as a triangle singularity

Abstract

We present a model for the $J/\psi \Lambda$ spectrum in $B^{-}\to J/\psi \Lambda \bar{p}$ decays, including the $P_{\psi s}^{\Lambda }(4338)$ baryon recently observed by the LHCb collaboration. We assume production via triangle diagrams which couple to the final state via non-perturbative interactions which are constrained by heavy-quark and $S{U}_3$-flavor symmetry. The bulk of the distribution is described by a triangle diagram with a color-favored electroweak vertex, while the sharp $P_{\psi s}^{\Lambda }(4338)$ enhancement is due to the triangle singularity in another diagram featuring a $1/2^{-}$ baryon consistent with ${\Sigma }_c(2800)$. We predict a comparable $P_{\psi s}^{\Lambda }(4338)$ signal in ${\eta }_c\Lambda$, and anticipate possible large isospin mixing effects through decays to $J/\psi {\Sigma }^0$ and ${\eta }_c{\Sigma }^0$

Comments: 14 pages, 2 figures