Measurement of the proton form factor by studying $e^{+} e^{-}rightarrow pbar{p}$

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of $e^{+}e^{-}rightarrow pbar{p}$ at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal $(|G_{E}|= |G_{M}|)$. In addition, the ratio of electric to magnetic form factors, $|G_{E}/G_{M}|$, and $|G_{M}|$ are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at $sqrt{s}=$ 2232.4 and 2400.0 MeV and a combined sample at $sqrt{s}$ = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BaBar, improving the overall uncertainty by about 30%. The $|G_{E}/G_{M}|$ ratios are close to unity and consistent with BaBar results in the same $q^{2}$ region, which indicates the data are consistent with the assumption that $|G_{E}|=|G_{M}|$ within uncertainties.

Observation of $J/psi rightarrow pbar{p}a_{0}(980)$ at BESIII

Using $2.25times10^{8}$ $J/psi$ events collected with the BESIII detector at the BEPCII storage rings, we observe for the first time the process $J/psirightarrow pbar{p}a_{0}(980)$, $a_{0}(980)rightarrow pi^{0}eta$ with a significance of $6.5sigma$ ($3.2sigma$ including systematic uncertainties). The product branching fraction of $J/psirightarrow pbar{p}a_{0}(980)rightarrow pbar{p}pi^{0}eta$ is measured to be $(6.8pm1.2pm1.3)times 10^{-5}$, where the first error is statistical and the second is systematic. This measurement provides information on the $a_{0}$ production near threshold coupling to $pbar{p}$ and improves the understanding of the dynamics of $J/psi$ decays to four body processes.