BESIII reports Born cross sections for e+e- to p pbar at 47 energies between 3.51 and 4.95 GeV and determines |GE/GM| and |GM| for the first time from angular distributions at large timelike momentum transfer.
Observation of a Broad Structure in the $\pi^+\pi^-J/\psi$ Mass Spectrum around 4.26 GeV/$c^2$
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abstract
We study initial-state radiation events, $e^+e^- \to \gamma_{ISR}\pi^+\pi^-J/\psi$, with data collected with the BaBar detector. We observe an accumulation of events near 4.26 GeV/$c^2$ in the invariant-mass spectrum of $\pi^+\pi^-J/\psi$. Fits of the mass spectrum indicate that a broad resonance with a mass of about 4.26 GeV/$c^2$ is required to describe the observed structure. The presence of additional narrow resonances cannot be excluded. The fitted width of the broad resonance is 50 to 90 MeV/$c^2$, depending on the fit hypothesis.
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Joint Dalitz decomposition of two e+e- processes with dispersive pi pi / KKbar final-state interactions shows a non-resonant production term is required and extracts Breit-Wigner parameters for Zc(3900), Y(4220), and Y(4320).
A coupled-channel framework is developed and fitted to BESIII data on vector charmonium-like states in the 4.1-4.6 GeV range, concluding that coupled-channel effects with dynamically generated poles explain the line shapes.
QCD sum rules predict Λ_c Σ_c hexaquark ground-state masses around 5.8 GeV, above threshold and consistent with no bound state observed by BESIII.
A constituent quark model predicts masses of 1.9, 4.2, and 6.6 GeV for light, charmonium-like, and fully-charm 1^{-+} tetraquarks along with decay ratios for specific two-body channels and rules out η1(1855) as a compact tetraquark.
Constituent quark model with imported meson parameters predicts lowest 1-- P-wave tetraquark mass near 4.15 GeV and proposes that ψ(4230), ψ(4360), ψ(4660), and Υ(10753) may be such states with possible multiples near 4.36 GeV.
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