We report the measurement of the inclusive cross sections for e^{+}e^{-}→nOCH (where nOCH denotes non-open charm hadrons) with improved precision at center-of-mass (c.m.) energies from 3.645 to ...3.871 GeV. We observe three resonances: R(3760), R(3780), and R(3810) with significances of 8.1σ, 13.7σ, and 8.8σ, respectively. The R(3810) state is observed for the first time, while the R(3760) and R(3780) states are observed for the first time in the nOCH cross sections. Two sets of resonance parameters describe the energy-dependent line shape of the cross sections well. In set I set II, the R(3810) state has mass (3805.7±1.1±2.7) (3805.7±1.1±2.7) MeV/c^{2}, total width (11.6±2.9±1.9) (11.5±2.8±1.9) MeV, and an electronic width multiplied by the nOCH decay branching fraction of (10.9±3.8±2.5) (11.0±3.4±2.5) eV. In addition, we measure the branching fractions BR(3760)→nOCH=(25.2±16.1±30.4)%(6.4±4.8±7.7)% and BR(3780)→nOCH=(12.3±6.6±8.3)%(10.4±4.8±7.0)% for the first time. The R(3760) state can be interpreted as an open-charm (OC) molecular state, but containing a simple four-quark state component. The R(3810) state can be interpreted as a hadrocharmonium state.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e^{+}e^{-}→Σ^{+}Σover ¯^{-} is studied at center-of-mass energies sqrts=2.3960, 2.6454, and 2.9000 GeV. ...Using a fully differential angular description of the final state particles, both the relative magnitude and phase information of the Σ^{+} electromagnetic form factors in the timelike region are extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ=-0.67±0.29(stat)±0.18(syst) at sqrts=2.3960 GeV, ΔΦ=55°±19°(stat)±14°(syst) at sqrts=2.6454 GeV, and 78°±22°(stat)±9°(syst) at sqrts=2.9000 GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
Based on ( 10 087 ± 44 ) × 10 6 J / ψ events collected with the BESIII detector, a partial wave analysis of the decay J / ψ → γ K S 0 K S 0 η ′ is performed. The mass and width of the X ( 2370 ) are ...measured to be 2395 ± 11 ( stat ) − 94 + 26 ( syst ) MeV / c 2 and 188 − 17 + 18 ( stat ) − 33 + 124 ( syst ) MeV , respectively. The corresponding product branching fraction is B J / ψ → γ X ( 2370 ) × B X ( 2370 ) → f 0 ( 980 ) η ′ × B f 0 ( 980 ) → K S 0 K S 0 = ( 1.31 ± 0.22 ( stat ) − 0.84 + 2.85 ( syst ) ) × 10 − 5 . The statistical significance of the X ( 2370 ) is greater than 11.7 σ and the spin parity is determined to be 0 − + for the first time. The measured mass and spin parity of the X ( 2370 ) are consistent with the predictions of the lightest pseudoscalar glueball. Published by the American Physical Society 2024
Based on ( 27.12 ± 0.14 ) × 10 8 ψ ( 2 S ) events collected by the BESIII detector, we search for the decay η c ( 2 S ) → π + π − η c via ψ ( 2 S ) → γ η c ( 2 S ) . No significant signal is ...observed, and the upper limit on the product branching fraction B ( ψ ( 2 S ) → γ η c ( 2 S ) ) × B ( η c ( 2 S ) → π + π − η c ) is determined to be 2.21 × 10 − 5 at the 90% confidence level. In addition, the η c ( 2 S ) → π + π − K S 0 K ± π ∓ decay is studied via ψ ( 2 S ) → γ η c ( 2 S ) and is observed with a statistical significance of 10 σ for the first time. The branching fraction of η c ( 2 S ) → π + π − K S 0 K ± π ∓ is determined to be ( 1.33 ± 0.11 ± 0.40 ± 0.95 ) × 10 − 2 , where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the quoted B ( ψ ( 2 S ) → γ η c ( 2 S ) ) . Published by the American Physical Society 2024
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