A practical parametrization for line shapes of near-threshold states

Understand

Numerous quarkonium(like) states lying near $S$-wave thresholds are observed experimentally.

• We propose a self-consistent approach to these near-threshold states compatible with unitarity and analyticity.
• The underlying coupled-channel system includes a bare pole and an arbitrary number of elastic and inelastic channels treated fully nonperturbatively.
• The resulting analytical parametrization is ideally suited for a combined analysis of the data available in various channels that is exemplified by an excellent overall description of the data for the charged $Z_b(10610)$ and $Z_b(10650)$ states.