Based on (106.41±0.86)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the branching fractions of ψ(3686)→π+π-J/ψ, J/ψ→e+e-, and J/ψ→μ+μ- are measured. We obtain B[ψ(3686)→π+π-J/ψ]=(34.98±0.02±0.45)%, B[J/ψ→e+e-]=(5.983±0.007±0.037)%, and B[J/ψ→μ+μ-]=(5.973±0.007±0.038)%. The measurement of B[ψ(3686)→π+π-J/ψ] confirms the CLEO-c measurement, and is apparently larger than the others. The measured J/ψ leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to B[J/ψ→l+l-]=(5.978±0.005±0.040)% by averaging over the e+e- and μ+μ- channels and a ratio of B[J/ψ→e+e-]/B[J/ψ→μ+μ-]=1.0017±0.0017±0.0033, which tests e-μ universality at the four tenths of a percent level. All the measurements presented in this paper are the most precise in the world to date.

We study the process e+ e- →(D* D*)± π∓ at a center-of-mass energy of 4.26 GeV using a 827  pb(-1) data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be (137±9±15)  pb. We observe a structure near the (D* D*)± threshold in the π∓ recoil mass spectrum, which we denote as the Zc±(4025). The measured mass and width of the structure are (4026.3±2.6±3.7)  MeV/c2 and (24.8±5.6±7.7)  MeV, respectively. Its production ratio σ(e+ e- → Zc±(4025)π∓ → (D* D*)± π∓)/σ(e+ e- → (D* D*)± π∓) is determined to be 0.65±0.09±0.06. The first uncertainties are statistical and the second are systematic.

Using a sample of 1.06×108 ψ(2S) events collected with the BESIII detector at BEPCII, the decay ψ(2S)→pp̄η is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524±5-4+10 MeV/c2 and a width of 130-24-10+27+57 MeV/c2 is dominant in the decay; the product branching fraction is determined to be B(ψ(2S)→N(1535)p̄)×B(N(1535)→pη)+c.c.=(5. 2±0.3-1.2+3.2)×10-5. Furthermore, the branching fraction of ψ(2S)→pp̄η is measured to be (6.4±0.2±0.6) ×10-5. Here, the first error is statistical and the second is systematic. © 2013 American Physical Society.

With a sample of 225.3 × 106 J/φ events taken with the BESIII detector, the decay J/φ → γ3 (π+ π-) is analyzed. A structure at 1.84 GeV/c2 is observed in the 3(π+ π-) invariant mass spectrum with a statistical significance of 7.6σ. The mass and width are measured to be M = 1842.2 ± 4.2-2.6+7.1 MeV/c2 and Γ = 83 ± 14 ± 11 MeV. The product branching fraction is determined to be B (J/φ → γX(1840)) × B(X(1840) → 3(π+ π-)) = (2.44 ± 0.36-0.74+0.60) × 10-5. No η′ signals are observed in the 3(π+ π-) invariant mass spectrum, and the upper limit of the branching fraction for the decay η′ → 3(π+ π-) is set to be 3.1 × 10-5 at a 90% confidence level.