The process e+e−→ pp̄π0has been studied by analyzing data collected at (formula presented) GeV, at (formula presented) GeV, and during a ψ(3770) line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of p̄pπ0in the vicinity of the ψ(3770) is measured, and the Born cross section of ψ(3770) → p̄pπ0is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5 σ are found. The solutions for the Born cross section of ψ(3770) → p̄pπ0are 33.8 ± 1.8 ± 2.1 pb and (formula presented) pb (< 0.22 pb at a 90% confidence level). Using the estimated cross section and a constant decay amplitude approximation, the cross section σ(p̄p → ψ(3770)π0) is calculated for the kinematic situation of the planned P̄ANDA experiment. The maximum cross section corresponding to the two solutions is expected to be less than 0.79 nb at 90% confidence level and 122 ± 10 nb at a center-of-mass energy of 5.26 GeV.

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.

Using a sample of 1.3 × 10(9)  J/ψ events collected with the BESIII detector, we report the first observation of η(')→π(+)π(-)π(+)π(-) and η(')→π(+)π(-)π(0)π(0). The measured branching fractions are B(η(')→π(+)π(-)π(+)π(-)) = [8.53 ± 0.69(stat.) ± 0.64(syst.)]×10(-5) and B(η(')→π(+)π(-)π(0) π(0)) = [1.82 ± 0.35(stat.) ± 0.18(syst.)] × 10(-4), which are consistent with theoretical predictions based on a combination of chiral perturbation theory and vector-meson dominance.

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.

An energy scan near the τ pair production threshold has been performed using the BESIII detector. About 24 pb-1 of data, distributed over four scan points, were collected. This analysis is based on τ pair decays to ee, eμ, eh, μμ, μh, hh, eρ, μρ and πρ final states, where h denotes a charged π or K. The mass of the τ lepton is measured from a maximum likelihood fit to the τ pair production cross-section data to be mτ = (1776.91 ± 0.12-0.13+0.10) MeV=c2, which is currently the most precise value in a single measurement.

We report a measurement of the branching fraction B(D+→μ+νμ)= [3.71±0.19(stat)±0.06(sys)]×10-4 based on 2.92fb-1 of data accumulated at s=3.773GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element |Vcd| determined from a global Standard Model fit, implies a value for the weak decay constant fD+=(203.2±5.3±1.8)MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for fD+, we find |Vcd|=0.2210±0.0058±0.0047. In either case, these are the most precise results for these quantities to date.

We perform an analysis of the D+→ K0Sπ+π0 Dalitz plot using a data set of 2.92 fb-1 of e+e- collisions at the ψ(3770) mass accumulated by the BESIII experiment, in which 166694 candidate events are selected with a background of 15.1%. The Dalitz plot is found to be well represented by a combination of six quasitwo- body decay channels [K0Sρ+, K0Sρ(1450)+, K∗0π+, K0 (1430)0π+, K (1680)0π+, κ0π+] plus a small nonresonant component. Using the fit fractions from this analysis, partial branching ratios are updated with higher precision than previous measurements.

A search for the rare decays of J/ψ → Dsρ+ + c.c. and J/ψ → D0K∗0 + c.c. is performed with a data sample of 225.3-million J/ψ events collected with the Beijing Spectrometer III detector. No evident signal is observed. Upper limits on the branching fractions are determined to be B(J/ψ → Ds ρ+ + c.c.) < 1.3 × 10-5 and B(J/ψ → D0K ∗0+ c.c.) < 2.5 × 10-6 at the 90% confidence level.

Based on a sample of (225.3 ± 2.8) × 106 J/ψ events collected with the BESIII detector, the electromagnetic Dalitz decays of J/ψ → Pe+e- (P = η'/η/π∗0) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/ψ → η' e+e-, J/ψ → η e+e-, and J/ψ → π0 e+e- are observed for the first time. The branching fractions are determined to be B(J/ψ → η' e+e-) = (5.81 ± 0.16 ± 0.31) × 10-5, B(J/ψ → η e+e-) = (1.16 ± 0.07 ± 0.06) × 10-5, and B(J/ψ → π0 e+e-) = (7.56 ± 1.32 ±0.50) × 10-7, where the first errors are statistical and the second ones systematic.