The LHCb state PψsΛ(4338) as a triangle singularity

We present a model for the J/ψΛ spectrum in B−→J/ψΛp¯ decays, including the PψsΛ(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 SU3-flavor symmetry. The bulk of the distribution is described by a triangle diagram with a color-favored electroweak vertex, while the sharp PψsΛ(4338) enhancement is due to the triangle singularity in another diagram featuring a 1/2− baryon consistent with Σc(2800). We predict a comparable PψsΛ(4338) signal in ηcΛ, and anticipate possible large isospin mixing effects through decays to J/ψΣ0 and ηcΣ0.