Quark spin structures of bottom-charmed threshold molecular states

TL;DR

This paper investigates the spin structures of bottom-charmed molecular states near threshold, highlighting how heavy quark spin symmetry applies differently compared to other heavy quark systems, with implications for exotic resonance properties.

Contribution

It introduces a novel analysis of heavy quark spin symmetry in bottom-charmed molecular states, emphasizing the dependence on separate parameters for bottom and charm quarks.

Findings

Spin structures of $B^{(*)} D^{(*)}$ molecular states are characterized.

Implications for properties of near-threshold resonances are discussed.

Differences from charmonium-like and bottomonium-like states are highlighted.

Abstract

The implementation of the heavy quark spin symmetry in possible molecular states at the mixed bottom-charm threshold is somewhat different from that at the open charm or bottom thresholds. In particular it depends on two parameters describing separately the symmetry for the bottom and for charmed quarks. The corresponding spin structures of the $S$-wave molecular states of the meson pairs $B^{(*)} D^{(*)}$ are discussed as well as their consequences for properties of possible near-threshold resonances, analogs of the known charmonium-like and bottomonium-like $X$ and $Z$ states.