Is X(2370) the lightest pseudoscalar glueball?
In plain words
In 2024 the BESIII experiment in Beijing found that the X(2370) particle has the spin and parity expected of the lightest pseudoscalar glueball and roughly the predicted mass. Whether it is made mainly of gluons is not established.
Precise statement
BESIII determined $J^{PC} = 0-+$ for $X(2370)$ with $M = 2395 \pm 11\,(\mathrm{stat}) +26/-94\,(\mathrm{syst})\,\mathrm{MeV}$ and width about 188 MeV (PRL 132, 181901, 2024); lattice QCD predicts the $0-+$ glueball near $2.4\ \text{to}\ 2.6\,\mathrm{GeV}$. Determine whether its production rate in $J/\psi$ radiative decays and its decay pattern match glueball expectations rather than a radial excitation of $\eta$ or $\eta'$. Answer: yes or no with a quantitative glueball fraction.
What would settle it
Measurement of $X(2370)$ branching fractions across several final states and of its two-photon width, compared with lattice QCD predictions of glueball production in $J/\psi$ radiative decay.
Status in the literature
Unverified note
The 2024 BESIII result fixed the quantum numbers, but the mass systematic uncertainty is large and decay-pattern tests were incomplete as of 2026.