Study of e+e−→ηϕ via initial state radiation at Belle

Abstract

Using 980 fb−1 of data collected on and around the ϒ(nS) (n=1, 2, 3, 4, 5) resonances with the Belle detector at the KEKB collider, we measure the cross section of e+e−→ηϕ from threshold to 3.95 GeV via initial state radiation. There are clear ϕ(1680) and J/ψ signals but no significant ϕ(2170) signal in the ηϕ final state. The branching fraction B[J/ψ→ηϕ] is measured to be (7.2±0.8±0.5)×10−4. The resonant parameters of ϕ(1680) are determined to be mϕ(1680)=(1696±8±10) MeV/c2 (statistical and systematic errors, respectively), Γϕ(1680)=(175±13±16) MeV and, depending on the possible presence of predominantly constructive or destructive interference between ϕ(1680) and continuum production, Γϕ(1680)e+e−·B[ϕ(1680)→ηϕ] and B[ϕ(1680)→ηϕ] are determined to be (75±10±11) eV and (25±12±2)% or (207±16±20) eV and (23±10±2)%, respectively. The upper limit for Γϕ(2170)e+e−·B[ϕ(2170)→ηϕ] is determined to be either 0.17 or 18.6 eV at the 90% confidence level.Received 1 September 2022Accepted 10 October 2022DOI:https://doi.org/10.1103/PhysRevD.107.012006Published 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 SocietyPhysics Subject Headings (PhySH)Research AreasHadronic decaysQuark modelParticles & Fields