• Open Access

Evidence for the Cusp Effect in η Decays into ηπ0π0

M. Ablikim et al. (BESIII Collaboration)
Phys. Rev. Lett. 130, 081901 – Published 24 February 2023
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Abstract

Using a sample of 4.3×105 ηηπ0π0 events selected from the ten billion J/ψ event dataset collected with the BESIII detector, we study the decay ηηπ0π0 within the framework of nonrelativistic effective field theory. Evidence for a structure at π+π mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, 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 ππ scattering length combination a0a2 is determined to be 0.226±0.060stat±0.013syst, which is in good agreement with theoretical calculation of 0.2644±0.0051.

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  • 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

Physics Subject Headings (PhySH)

Particles & FieldsNuclear Physics

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Vol. 130, Iss. 8 — 24 February 2023

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