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

TL;DR

This paper investigates whether the $X(2900)$ particle observed at LHCb can be explained as a kinematical cusp effect from specific hadronic interactions, challenging the resonance interpretation.

Contribution

It introduces a model using a triangle diagram with final state interactions to fit the Dalitz plot, exploring both cusp and resonance scenarios for $X(2900)$.

Findings

A good fit is achieved without invoking $ar{D}K$ resonances.

Strong final state interactions can produce resonances, improving the fit.

Evidence for resonance generation is inconclusive.

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 $\bar D^*K^*$ and $\bar D_1 K^*$ 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.