BESIII Collaboration Revives 35-Year-Old Standard Model Test

BESIII physicists have revived a long‑neglected experimental test of a core prediction of the Standard Model, employing a technique that had not been used for more than three decades. The collaboration, operating the BEPCII collider in China, applied this method to study the decays of charmonium states with unprecedented precision.

The experiment focused on a detailed analysis of the angular distributions and invariant‑mass spectra of multi‑body decays of the \(J/\psi\) meson. By reconstructing thousands of decay events and comparing the observed patterns to the theoretical expectations derived from quantum chromodynamics and electroweak theory, the team confirmed the Standard Model’s predictions within the experimental uncertainties. The results also set new limits on possible contributions from physics beyond the Standard Model, such as exotic resonances or non‑standard couplings.

These findings reinforce the robustness of the Standard Model while demonstrating the value of revisiting older experimental techniques with modern detectors and data‑analysis tools. The BESIII Collaboration plans to extend the study to other charmonium and light‑meson decays, aiming to further test the limits of the theory and search for subtle signs of new physics.