Abstract
The nature of the bottomonium-like states and is studied by calculating the compositeness () in those resonances. We first consider uncoupled isovector -wave scattering of within the framework of effective-range expansion (ERE). Expressions for the scattering length () and effective range () are derived exclusively in terms of the masses and widths of the two states. We then develop compositeness within ERE for the resonance case and deduce the expression , which is then applied to the systems of interest. Finally, the actual compositeness parameters are calculated in terms of resonance pole positions and their experimental branching ratios into by using the method of [U. G. Meißner and J. A. Oller, Phys. Lett. B 751, 59 (2015)]. We find the values and for the and , respectively. We also compare the ERE with Breit-Wigner and Flatté parametrizations to discuss the applicability of the last two for near-threshold resonances with explicit examples.
- Received 22 March 2016
DOI:https://doi.org/10.1103/PhysRevD.94.014012
© 2016 American Physical Society