Electromagnetic form factors are fundamental observables that describe the electric and magnetic structure of hadrons and provide keys to understand the strong interaction. At the Beijing Spectrometer (BESIII), form factors have been measured for different baryons in the time-like region for the first time or with the best precision. The results are presented with examples focused on but not limited to the proton/neutron, the Λ, with a strange quark, and the Λ_c, with a charm quark.

The standard model of particle physics is a well-tested theoretical framework, but there are still some issues that deserve experimental and theoretical investigation. The $\mathrm{\Xi }$ resonances with strangeness $S=-2$, the so-called doubly-strange hyperon, can provide important information to further test the standard model by studying their electromagnetic form factors, such as probing the limitation of the quark models and spotting unrevealed aspects of the QCD description of the structure of hadron resonances. In this work, we review some recent studies of the electromagnetic form factors on doubly-strange hyperons in pair production from positron–electron annihilation experiment.

For over 100 y, scientists have investigated the properties of the proton, which is one of the most abundant components of visible matter in the universe. Nevertheless, researchers do not fully understand many details about its internal structure and dynamics. Time-like electromagnetic form factors are some of the observable quantities that can help us achieve a deeper understanding. In this review article, we present an overview of the current experimental status in this field, consisting of measurements of the time-like reactions $e^{+}{e}^{-}\to p\overline{p}$ and $p\overline{p}\to e^{+}{e}^{-}$ and future measurements of $p\overline{p}\to {\mu }^{+}{\mu }^{-}$. The focus is put on recent high-precision results of the reaction $e^{+}{e}^{-}\to p\overline{p}$ that have been obtained after analyzing 688.5 pb${}^{-1}$ of data taken at the BESIII experiment. They are compared to and put into perspective with results from previous measurements in this channel. We discuss the channels $p\overline{p}\to e^{+}{e}^{-}$ and $p\overline{p}\to {\mu }^{+}{\mu }^{-}$ in terms of the few existing, as well as future measurements, which the PANDA experiment will perform. Finally, we review several new theoretical models and phenomenological approaches inspired by the BESIII high-precision results and then discuss their implications for a deeper understanding of the proton’s structure and inner dynamics.

The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, calorimetric type, high-energy-resolution detector for the precise measurement of high-energy electrons, gamma rays, and nuclei from deep space. The DAMPE electromagnetic calorimeter consists of bismuth germanate (BGO) crystals that can measure incident hadron energies from 50 GeV to 100 TeV. For an inorganic scintillator, such as BGO, the non-linear fluorescence response when measuring ions contributes to the difference between the experimental data and Monte Carlo simulations. This paper reports the BGO quenching non-linearity occuring in the DAMPE experiment. The ionization energy response of BGO to several kinds of ions lighter than iron are investigated by conducting beam tests and analyzing flight data. We compare the scintillator output with the energy loss according to GEANT4 simulations and determine the quenching parameters. The combined result of beam test and flight experiment shows that the quenching effect strongly depends on the density of the ionization energy loss.

Using $e^{+}{e}^{-}\to \mathrm{\text{hadrons}}$ data collected with the CLEO-III detector at the Cornell Electron Storage Ring, we study the inclusive production of baryons/antibaryons $(p,\Lambda )$ and mesons ($\varphi$ and $f_2(1270)$) in gluon-fragmentation and quark-fragmentation processes. We first corroborate previous per-event total particle yields in ${\rm Y}(1\mathrm{S})\to ggg$ compared with nearby continuum ($e^{+}{e}^{-}\to q\overline{q}$) indicating greater ($\sim \times 2$) per-event yields of baryons in 3-gluon fragmentation. We find similar results when we extend that comparison to include the ${\rm Y}(2\mathrm{S})$ and ${\rm Y}(3\mathrm{S})$ resonances. With higher statistics, we now also probe the momentum dependence of these per-event particle yields. Next, we compare particle production in the photon-tagged process ${\rm Y}(1\mathrm{S})\to gg\gamma$ with that in $e^{+}{e}^{-}\to q\overline{q}\gamma$ events, to allow comparison of two-parton with three-parton particle-specific fragmentation. For each particle, we determine the “enhancement” ratio, defined as the ratio of particle yields per gluon-fragmentation event compared to quark-fragmentation event. Thus defined, an enhancement of 1.0 implies equal per-event production in gluon and quark fragmentation. In the photon-tagged analysis (${\rm Y}(1\mathrm{S})\to gg\gamma$ compared to $e^{+}{e}^{-}\to q\overline{q}\gamma$), we find almost no enhancement for protons ($\sim 1.2\pm 0.1$), but a significant enhancement ($\sim 1.9\pm 0.3$) for $\Lambda$’s. This small measured proton enhancement rate is supported by a study of baryon production in ${\chi }_{b2}\to gg\to p+X$ relative to ${\chi }_{b1}\to q\overline{q}g\to p+X$. Overall, per-event baryon production in radiative two-gluon fragmentation is somewhat smaller than that observed in three-gluon decays of the ${\rm Y}(1\mathrm{S})$. Our results for baryon production are inconsistent with the predictions of the JETSET (7.3) fragmentation model.