Kinematical Cusp and Resonance Interpretations of the $X(2900)$

Abstract

We examine whether the LHCb vector $ud\bar{c}\bar{s}$ state $X(2900)$ can be interpreted as a kinematical cusp effect arising from ${\bar{D}}^{\ast }{K}^{\ast }$ and ${\bar{D}}_1{K}^{\ast }$ interactions. The production amplitude is modelled as a triangle diagram with hadronic final state interactions. A satisfactory fit to the Dalitz plot projection is obtained that leverages the singularities of the production diagram without the need for $\bar{D}K$ resonances. A somewhat better fit is obtained if the final state interactions are strong enough to generate resonances, although the evidence in favour of this scenario is not conclusive.

Comments: 10 pages, 3 figures. Version to appear in Physics Letters B