[en] Using a $3.19{\mathrm{fb}}^{-1}$ data sample collected at the $\sqrt{s}=4.178\mathrm{GeV}$ with the BESIII detector, we search for the rare decay $D_s^{+}\to p\overline{p}{e}^{+}{\nu }_e$. No significant signal is observed, and an upper limit of $\mathcal{B}(D_s^{+}\to p\overline{p}{e}^{+}{\nu }_e)<2.0\times {10}^{-4}$ is set at the 90% confidence level. This measurement is useful input in understanding the baryonic transition of $D_s^{+}$ mesons.

[en] The electromagnetic process $e^{+}{e}^{-}\to p\overline{p}$ is studied with the initial-state-radiation technique using 7.5 fb⁻¹ of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/$c^2$ using the $p\overline{p}$ invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.

[en] Based on 586 $\mathrm{p}{\mathrm{b}}^{-\mathrm{1}}$ of $e^{+}{e}^{-}$ annihilation data collected at a center-of-mass energy of $\sqrt{s}=4.6\mathrm{GeV}$ with the BESIII detector at the BEPCII collider, the absolute branching fraction of ${\mathrm{\Lambda }}_c^{+}\to p{K}_{\mathrm{S}}^0\eta$ decays is measured for the first time to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}_{\mathrm{S}}^0\eta )=(0.414\pm 0.084\pm 0.028)\text{\%}$, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction $\frac{\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}_{\mathrm{S}}^0\eta )}{\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})}$, and consistent with theoretical predictions of SU(3) flavor symmetry.

[en] The Born cross sections of the $e^{+}{e}^{-}\to {\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$ and $e^{+}{e}^{-}\to {\mathrm{\Sigma }}^{-}{\overline{\mathrm{\Sigma }}}^{+}$ processes are determined for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the ${\mathrm{\Sigma }}^{+}$ and ${\mathrm{\Sigma }}^{-}$ is consistent with 3. In addition, ratios of the ${\mathrm{\Sigma }}^{+}$ electric and magnetic form factors, $|G_E/G_M|$, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the ${\mathrm{\Sigma }}^{\pm }$ form factors require more theoretical discussions for the hyperons.

[en] The reactions γp → ηp and γp → η'p are measured from their thresholds up to the center-of-mass energy W = 1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η' threshold, W = 1896 MeV (Eγ =1447 MeV). Within the framework of a revised η MAID isobar model, the cusp, in connection with a steep rise of the η' total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2-state to both ηp and η'p. Including the new high-accuracy results in the η MAID fit to available η and η0 photoproduction data allows the determination of the Nð1895Þ1=2 ^- properties.

[en] Here, the largest, at the moment, statistics of 7 × 10 ⁶ η → 3π ⁰ decays, based on 6.2 × 10 ⁷ η mesons produced in the γp → ηp reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η → 3π ⁰ dynamics beyond its conventional parametrization with just the quadratic slope parameter α and enabled, for the first time, a mea- surement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center.

[en] Using $e^{+}{e}^{-}$ collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of about 500 pb⁻¹, we measure the cross sections and effective form factors for the process $e^{+}{e}^{-}\to {\mathrm{\Xi }}^0{\overline{\mathrm{\Xi }}}^0$ utilizing a single-tag method. A fit to the cross section of $e^{+}{e}^{-}\to {\mathrm{\Xi }}^0{\overline{\mathrm{\Xi }}}^0$ with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes $e^{+}{e}^{-}\to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ and ${\mathrm{\Xi }}^0{\overline{\mathrm{\Xi }}}^0$ is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry.

[en] An experimental study of the η' → π ⁰π ⁰η → 6$\mathrm{\gamma <!--\; ??\; -->}$ decay has been conducted with the best up- to-date statistical accuracy, by measuring η' mesons produced in the $\mathrm{\gamma <!--\; ??\; -->}$p → η'p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η' → π ⁰π ⁰η matrix element are consistent with the most recent results for η' → ππη decays, but have smaller uncertainties. Finally, the available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π ⁺π ^- mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the ππ scattering length combination, a ₀ - a ₂, extracted from K → 3π decays. Authors:

[en] Using 5.9 pb⁻¹ of $e^{+}{e}^{-}$ annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of $e^{+}{e}^{-}\to K_S^{0}X$ (where $X=\text{anything}$). From a fit to these observed cross sections with the sum of continuum and $\psi (3686)$ and $J/\psi$ Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the product of $\psi (3686)$ leptonic width and inclusive decay branching fraction ${\mathrm{\Gamma }}_{\psi (3686)}^{ee}\mathcal{B}(\psi (3686)\to K_S^{0}X)=(373.8\pm 6.7\pm 20.0)$ eV, and assuming ${\mathrm{\Gamma }}_{\psi (3686)}^{ee}$ is $(2.33\pm 0.04)$ keV from PDG value, we measure $\mathcal{B}(\psi (3686)\to K_S^{0}X)=(16.04\pm 0.29\pm 0.90)\text{\%}$, where the first uncertainty is statistical and the second is systematic.

[en] Born cross sections for the processes $e^{+}{e}^{-}\to \omega \eta$ and $e^{+}{e}^{-}\to \omega {\pi }^0$ have been determined for center-of-mass energies between 2.00 and 3.08 GeV with the BESIII detector at the BEPCII collider. The results obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the $e^{+}{e}^{-}\to \omega \eta$ cross sections, a resonance with a mass of $(2176\pm 24\pm 3)\text{MeV}/c^2$ and a width of $(89\pm 50\pm 5)\text{MeV}$ is observed with a significance of 6.2σ. Its properties are consistent with the $\varphi (2170)$. In the $e^{+}{e}^{-}\to \omega {\pi }^0$ cross sections, a resonance denoted $Y(2040)$ is observed with a significance of more than 10σ. Its mass and width are determined to be $(2034\pm 13\pm 9)\text{MeV}/c^2$ and $(234\pm 30\pm 25)\text{MeV}$, respectively, where the first uncertainties are statistical and the second ones are systematic.