Abstract
Using a sample of events selected from the ten billion event dataset collected with the BESIII detector, we study the decay within the framework of nonrelativistic effective field theory. Evidence for a structure at mass threshold is observed in the invariant mass spectrum of with a statistical significance of around , which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the scattering length combination is determined to be , which is in good agreement with theoretical calculation of .
- Received 6 July 2022
- Revised 19 November 2022
- Accepted 20 January 2023
DOI:https://doi.org/10.1103/PhysRevLett.130.081901
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society