Observation of the Zcs(3985) strange four-quark meson In the March 12th, 2021 issue of Physical Review Letters, the BESIII collaboration reports the discovery of an exotic multi-quark structure, dubbed the Zcs(3985), that is produced in the process of e^+ e^-→K^+ (D_s^- D^(*0)+D_s^(*-) D^0) at an e^+ e^- center-of-mass energy of 4.68 GeV. The Zcs(3985) is observed to decay to a charged strange-charmed meson plus a neutral charmed meson, i.e., D_s^- D^(*0)+D_s^(*-) D^0, and has a mass of 3.98 GeV/c2. This is the first candidate for a tetra-quark meson containing hidden-charm with non-zero strangeness. This paper was selected as one of that issue’s and "Editors' Suggestion" and prominently featured on the APS synopsis website.

White Paper on the Future Physics Programme of BESIII The BESIII Collaboration officially released a draft version of its White Paper on the Future Physics Programme of BESIII ("white paper") at arXiv.org on Dec. 13. Feedback on the paper from international peers will be collected for two weeks. The release of the white paper signifies a new stage for BESIII physics research and China’s experimental hadron physics research.

BESIII Observes Polarization of Baryons in J/ψ Decay The BESIII collaboration observed baryon polarization in baryon-antibaryon (matter-antimatter particle) events from J/ψ particles produced at the BEPCII collider. The paper was published in Nature Physics on May 6.

BESIII Observes New Leptonic Decay Mode for D Meson The BESIII collaboration has reported the world's first observation of the decay D+ → τ+ν in a newly published Physical Review Letters paper that has been highlighted by the journal as an "Editors' Suggestion.” This is the second type of pure leptonic decay of the D+ meson.

BESIII Accumulates 10 Billion J/ψ Events The BESIII detector finished accumulating a sample of 10 billion J/ψ events together with a continuum data sample on Feb. 11. The 10 billion J/ψ-event sample accumulated at BESIII is the world's largest data sample produced directly from electron-positron annihilations.

Zc(3900) is on the top of the "Highlights of the Year" Quarks come in twos and threes—or so nearly every experiment has told us. This summer, the BESIII Collaboration in China and the Belle Collaboration in Japan reported they had sorted through the debris of high-energy electron-positron collisions and seen a mysterious particle that appeared to contain four quarks. Though other explanations for the nature of the particle, dubbed Zc(3900), are possible, the “tetraquark” interpretation may be gaining traction: BESIII has since seen a series of other particles that appear to contain four quarks.

New Vector Particles Observed at BESIII The Beijing Spectrometer Experiment (BESIII) has announced the observation of more new charmonium-like states.

Observation of a charged charmoniumlike structure at BESIII An international team of scientists that operate the BESIII Experiment at the Beijing Electron Positron Collider in China recently began a series of specialized studies aiming at an understanding of the anomalous "Y(4260)" particle. As a striking and unexpected first observation from these new studies, the collaboration has reported that the Y(4260) particle in fact decays to a new, and perhaps even more mysterious, particle that they named the "Zc(3900).”