An assessment of Υ-states above 𝐁𝐁̅-threshold using a constituent-quark-model based meson-meson coupled-channels framework

The Υ(10753) state has been recently observed by the Belle and Belle II collaborations with enough global significance to motivate an assessment of the high-energy spectrum usually predicted by any reasonable naïve quark model. In the framework of a constituent quark model which satisfactorily describes a wide range of properties of conventional hadrons containing heavy quarks, the quark-antiquark and meson-meson degrees of freedom have been incorporated with the goal of elucidating the influence of open-bottom meson-meson thresholds into the Υ states whose masses are within the energy range of the Υ(10753)'s mass. It is well known that such effects could be relevant enough as to generate dynamically new states and thus provide a plausible explanation of the nature of the Υ(10753) state. In particular, we have performed a coupled-channels calculation in which the bare states Υ(4S), Υ(3D), Υ(5S) and Υ(4D) are considered together with the threshold channels BB̅, BB̅^∗, B^∗B̅^∗, B_sB̅_s, B_sB̅_s^∗ and B_s^∗B̅_s^∗. Among the results we have described, the following conclusions are of particular interest: (i) a richer complex spectrum is gained when thresholds are present and bare bound states are sufficiently non-relativistic; (ii) those poles obtained in the complex energy plane do not have to appear as simple peaks in the relevant cross sections; and (iii) the Υ(10750) candidate is interpreted as a dressed hadronic resonance whose structure is an equally mixture of a conventional bb̅ state and B^∗B̅^∗ molecule.