Here, we observe the decay ψ(3686) → n$\bar{n}$ for the first time and measure ψ(3686) → p$\bar{p}$ with improved accuracy by using 1.07 × 108 ψ(3686) events collected with the BESIII detector. The ...measured branching fractions are $\mathscr{B}$(ψ(3686) → n$\bar{n}$) = (3.06 ± 0.06 ± 0.14) × 10-4 and $\mathscr{B}$(ψ(3686) → p$\bar{p}$) = (3.05±0.02±0.12) × 10-4. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey 1 + α cos2 θ, we determine the α parameters to be αn$\bar{n}$ = 0.68 ± 0.12 ± 0.11 and αp$\bar{p}$ = 1.03 ± 0.06 ± 0.03 for ψ(3686) → n$\bar{n}$ and ψ(3686) → p$\bar{p}$, respectively.
Using 2.93 fb(-1) of e(+)e(-) collision data collected with the BESIII detector at a center-of-mass energy of 3.773 GeV, we measure the absolute branching fractions of the decays D-0 -> ...K(-)e(+)nu(e) and D+ -> (K) over bar (0)e(+)nu(e) to be (3.567 +/- 0.031(stat) +/- 0.025(syst))% and (8.68 +/- 0.14(stat) +/- 0.16(syst))%, respectively. Starting with the process e(+)e(- ) -> D (D) over bar, a new reconstruction method is employed to select events that contain candidates for both D -> (K) over bare(+)nu(e) and (D) over bar -> Ke(-)(nu) over bar (e) decays. The branching fractions reported in this work are consistent within uncertainties with previous BESIII measurements that selected events containing D -> (K) over bare(+)nu(e) and hadronic (D) over bar decays. Combining our results with the lifetimes of the D degrees and D+ mesons and the previous BESIII measurements leads to a ratio of the two decay partial widths of (Gamma) over bar (D0 -> K-e+)(nu e)/(Gamma) over bar (D+ -> (K) over bar 0e+)(nu e) = 1.039 +/- 0.021. This ratio supports isospin symmetry in the D-0 -> K(-)e(+)nu(e) and D+ -> (K) over bar (0)e(+)nu(e) decays within 1.9 sigma.
The Born cross sections for the process e+e− → η′π+π− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected ...with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3 σ and a mass and width of M = ( 2111 ± 43 ± 25 ) MeV / c2 and Γ = ( 135 ± 34 ± 30 ) MeV , where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e− → η′ π+π− and BESIII in e+e− → ωπ0 within two standard deviations.
► Heavy metal risk in urban sediments was inconsistent by three assessment approaches. ► The consistency derived from approach assumption and metal and sediment properties. ► Urbanization effect was ...not obvious on heavy metal contamination risks in sediments.
Numerous indices have been developed to assess environmental risk of heavy metals in surface sediments, including the total content based geoaccumulation index (
I
geo
), exchangeable fraction based risk assessment code (RAC), and biological toxicity test based sediment quality guidelines (SQGs). In this study, the three indices were applied to freshwater surface sediments from 10 sections along an urbanization gradient of the Grand Canal, China to assess the environmental risks of heavy metals (Cu, Pb, Zn, Cd, and Cr) and to understand discrepancies of risk assessment indices and urbanization effects regarding heavy metal contamination. Results showed that Cd, Zn, and Pb were the most enriched metals in urban sections assessed by
I
geo
and over 95% of the samples exceeded the Zn and Pb thresholds of the effect range low (ERL) of SQGs. According to RAC, Cu, Zn, Cd, and Cr had high risks of adversely affecting the water quality of the Grand Canal due to their remarkable portions of exchangeable fraction in surface sediment. However, Pb showed a relative low risk, and was largely bounded to Fe/Mn oxides in the urban surface sediments. Obviously, the three assessment indices were not consistent with each other in terms of predicting environmental risks attributed to heavy metals in the freshwater surface sediments of this study. It is recommended that risk assessment by SQGs should be revised according to availability and site specificity. However, the combination of the three indices gave us a comprehensive understanding of heavy metal risks in the urban surface sediments of the Grand Canal.
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