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T: Fachverband Teilchenphysik
T 15: Searches/BSM I
T 15.8: Vortrag
Montag, 16. März 2026, 18:00–18:15, KH 02.018
Search for X17 particle at the BESIII — •Hang Zhou1,2 and Achim Denig1,2 — 1Johannes Gutenberg University Mainz, Germany — 2Helmholtz Institute Mainz, Germany
The anomalous internal pair creation signals reported by the ATOMKI group suggest the emission of a new boson with an invariant mass of approximately 17 MeV, often referred to as X17. This hypothetical particle has been proposed as a mediator of a fifth force or as a portal between the Standard Model (SM) and a dark sector. Besides the ATOMKI measurements, several dedicated experiments, such as NA64, MEG II and PADME, have searched for X17-like signatures. So far, however, no independent experiment has conclusively confirmed the existence of X17. If X17 is a real boson, it should also be produced in processes beyond nuclear transitions. One suggested possibility is heavy meson decay, e.g. charmonium decay. Charmonium Dalitz decays, which are analogous to nuclear de-excitation with internal pair creation, offer an independent test of the X17 hypothesis and a unique environment to probe its couplings to second-generation quarks. Moreover, the available phase space in these decays is well suited for searches for MeV-scale dark photons that couple weakly to SM particles.
The BESIII experiment operating at the BEPCII e+e− accelerator, has collected world’s largest data sample in the τ-charm region. Using these data, a dedicated search for X17 in charmonium Dalitz decays is performed. This talk will present the analysis strategy and recent results from BESIII, providing a complementary and collider-based probe of the X17 scenario.
Keywords: X17; Dark photon; Dalitz decay; Charmonium