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Using 4.5 fb −1 of e + e − annihilation data samples collected at the center-of-mass energies ranging from 4.600 GeV to 4.699 GeV with the BESIII detector at the BEPCII collider, a first study of Λ + c decaying semileptonically into the inclusive pK − system Λ + c → pK − e + νe is performed. The Λ + c → pK − e + νe decay is observed with a significance of 8.2σ and the branching fraction is measured to be B(Λ + c → pK − e + νe) = (0.82 ± 0.15stat. ± 0.06syst.) × 10 −3 . In addition, first evidence for the decay Λ + c → Λ(1520)e + νe is obtained with a significance of 3.3σ and the branching fraction is measured to be B(Λ + c → Λ(1520)e + νe) = (1.36 ± 0.56stat. ± 0.14syst.) × 10 −3 . We also measure the branching fraction for Λ + c → pK − non−Λ(1520) e + νe to be B(Λ + c → pK − non−Λ(1520) e + νe) = (0.53 ± 0.15stat. ± 0.06syst.) × 10 −3 . Using a measurement of the inclusive semileptonic Λ + c branching fraction from BESIII, the relative branching fractions are determined to be [B(Λ + c → pK − e + νe)/B(Λ + c → Xe + νe)] = (2.1 ± 0.4stat. ± 0.1syst.)% and [B(Λ + c → Λ * (1520)e + νe)/B(Λ + c → Xe + νe)] = (3.4 ± 1.4stat. ± 0.4syst.)%. These measurements provide a clear confirmation that semileptonic Λ + c decays are not saturated by the Λℓ + ν ℓ final state.

Cross section measurements of the processes e + e − → ωπ 0 and ωη at center-of-mass energies between 3.773 and 4.701 GeVThe BESIII collaboration

The cross section of the process e + e − → ωπ 0 π 0 is measured at nineteen center-of-mass energies from 2.00 to 3.08 GeV using data collected with the BESIII detector at the BEPCII storage ring. A resonant structure around 2.20 GeV is observed with significance larger than 5σ. Using a coherent fit to the cross section line shape, the mass and width are determined to be M = 2223±16±11 MeV/c 2 and Γ = 51 ± 29 ± 21 MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.

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