Confirmation of an additional narrow vector state near 2.15 GeV

Determine whether an additional narrow vector state near 2.15 GeV is necessary to explain the observed line-shape behavior in the combined e^+e^- → φη, e^+e^- → φη′, and open-strange cross sections.

Background

The combined fit describes the broad structures through the excited-strangeonium baseline involving the φ(3S) and φ(2D) states and strange-meson-loop contributions, but it does not reproduce one high-precision BESIII φη data point near 2.16 GeV. Adding a narrow vector amplitude denoted by Y improves the fits and yields a mass near 2.15 GeV and a width of approximately 25 MeV.

The authors emphasize that the additional resonance interpretation is exploratory and is not established by the present data because the measured energy points have large bin sizes. They identify a finer energy scan in the 2.1–2.2 GeV region, together with a combined analysis of hidden- and open-strange final states, as necessary to determine whether the narrow state is genuinely required.

References

Our analysis indicates a preference for an additional narrow resonance contribution but does not by itself establish a new resonance due to the large bin size of the present measured energy points. More precise measurements, particularly a finer energy scan in the $2.1$--$2.2~\mathrm{GeV}$ region, together with a combined analysis of the $\phi\eta$, $\phi\eta{\prime}$, and open-strange final states, will be essential for determining whether an additional vector state is necessary for depicting the observed line shape behavior.

— Understanding the enhanced $φη^{\prime}$ decay mode of the $φ(2170)$ through strange-meson loops  (2608.14440 - Zhou et al., 14 Aug 2026) in Section V, 'The hints of an additional narrow structure near the φ(2170)'