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The complicated structure of the neutron cannot be calculated using first-principles calculations due to the large colour charge of quarks and the self-interaction of gluons. Its simplest structure observables are the electromagnetic form factors1, which probe our understanding of the strong interaction. Until now, a small amount of data has been available for the determination of the neutron structure from the time-like kinematical range. Here we present measurements of the Born cross section of electron–positron annihilation reactions into a neutron and anti-neutron pair, and determine the neutron’s effective form factor. The data were recorded with the BESIII experiment at centre-of-mass energies between 2.00 and 3.08 GeV using an integrated luminosity of 647.9 pb−1. Our results improve the statistics on the neutron form factor by more than a factor of 60 over previous measurements, demonstrating that the neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. The effective form factor of the neutron shows a periodic behaviour, similar to earlier observations of the proton form factor. Future works—both theoretical and experimental—will help illuminate the origin of this oscillation of the electromagnetic structure observables of the nucleon.Form factors encode the structure of nucleons. Measurements from electron–positron annihilation at BESIII reveal an oscillating behaviour of the neutron electromagnetic form factor, and clarify a long-standing photon–nucleon interaction puzzle.

A bstract We search for the radiative decays D + → γρ + and D + → γK *+ using 20.3 fb − 1 of e + e − annihilation data collected at the center-of-mass energy s = 3.773 GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and the upper limits on the branching fractions of D + → γρ + and D + → γK *+ at 90% confidence level are set to be 1.3 × 10 − 5 and 1.8 × 10 − 5 , respectively.

The uRANIA-V project foster the development of new technologies for thermal neutron detection with gaseous detectors. The first is the micro-Resistive WELL (μ-RWELL), a compact resistive Micro-Pattern-Gaseous Detector (MPGD) born for HEP applications. The second proposed technology is the surface-Resistive Plate Counter (sRPC). This detector is a novel type of RPC which principle of operation is based on surface resistivity. For both detectors different 10B4C converter have been exploited to detect thermal neutrons, achieving in both case overall efficiencies ranging between 5 and 10%.

A bstract Using (447.9 ± 2.3) million ψ (3686) events collected with the BESIII detector, the decays of χ cJ → ϕϕ ( J = 0 , 1 , 2) have been studied via the decay ψ (3686) → γχ cJ . The branching fractions of the decays χ cJ → ϕϕ ( J = 0 , 1 , 2) are determined to be (8 . 59 ± 0 . 27 ± 0 . 20) × 10 − 4 , (4 . 26 ± 0 . 13 ± 0 . 15) × 10 − 4 , and (12 . 67 ± 0 . 28 ± 0 . 33) × 10 − 4 , respectively, which are the most precise measurements to date. From a helicity amplitude analysis of the process ψ (3686) → γχ cJ , χ cJ → ϕϕ, ϕ → K + K − , the polarization parameters of the χ cJ → ϕϕ decays are determined for the first time.

Using e + e − collision data collected at the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, corresponding to an integrated luminosity of 7 . 33 fb − 1 , we determine the absolute branching fractions of fifteen hadronic D + s decays with a double-tag technique. In particular, we make precise measurements of the branching fractions B(D + s →K + K − π + )=(5.49±0.04±0.07)%, B(D + s →K 0 S K + )=(1.50±0.01±0.01)% and B(D + s →K + K − π + π 0 )=(5.50±0.05±0.11)%, where the first uncertainties are statistical and the second ones are systematic. The CP asymmetries in these decays are also measured and all are found to be compatible with zero.

A bstract Using 10 . 1 × 10 9 J/ψ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy s = 3 . 097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/ψ → D − e + ν e + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction ℬ( J / ψ  →  D − e + ν e  +  c . c .) < 7.1 × 10 −8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.

A bstract Using a total of 5 . 25 fb − 1 of e + e − collision data with center-of-mass energies from 4.236 to 4.600 GeV, we report the first observation of the process e + e − → ηψ (2 S ) with a statistical significance of 4.9 standard deviations. The data sets were collected by the BESIII detector operating at the BEPCII storage ring. We measure the yield of events integrated over center-of-mass energies and also present the energy dependence of the measured cross section.

In the framework of the uRANIA (u-Rwell Advanced Neutron Imaging Apparatus) project, we are developing innovative thermal neutron detectors based on resistive gaseous devices such as micro-Resistive WELL (μ-RWELL) and surface Resistive Plate Counter (sRPC). The μ-RWELL is a single amplification stage resistive MPGD developed for HEP applications. The amplification stage, based on the same Apical® foil used for the manufacturing of the GEM, is embedded through a resistive layer in the readout board. The resistive layer is realized by sputtering the back side of the Apical® foil with DiamondLike-Carbon (DLC). A cathode electrode, defining the gas conversion/drift gap, completes the detector mechanics. The deposition of a thin layer of 10 B4C on the cathode surface allows the thermal neutrons conversion into 7 Li and α ions, which can be easily detected in the active volume of the device. Results from tests performed with different detector layouts show that a thermal neutron (25 meV) detection efficiency up to 7% can be achieved with a single detector. A comparison between experimental data and the simulation of the detector behaviour has been performed. In parallel, we are proposing the development of thermal neutron detectors based on a novel RPC concept. The sRPC is a revolutionary RPC based on surface resistive electrodes realized by exploiting the well-established DLC sputtering technology on thin (50µm) polyimide foils, the same used in the manufacturing of the µ-RWELL. The DLC foil is glued onto a 2 mm thick float-glass. The 2 mm gas gap between the electrodes is ensured by spacers made of Delrin®, inserted without gluing at the edges of the glass supports. By replacing DLC with 10 B4C sputtered electrodes, the device becomes sensitive to thermal neutrons. Different layouts of 10 B4C coated electrodes have been tested, allowing to achieve efficiency up to 6%. The robustness, ease of construction, and scalability of the sRPC technology should allow the construction of cost-effective large area detector units as required by applications in homeland security (such as Radiation Portal Monitor).

We measure the branching fractions for seven D-s(+) two-body decays to pseudoscalar mesons, by analyzing data collected at root s = 4:178 similar to 4:226 GeV with the BESIII detector at the BEPCII collider. The branching fractions are determined to be B(D-s(+) -> K+eta ') = (2:68 +/- 0:17 +/- 0:17 +/- 0:08) x 10(-3), B(D-s(+) -> eta 'pi(+)) = (37:8 +/- 0:4 +/- 2:1 +/- 1:2) x 10(-3), B(D-s(+) -> K+eta) = (1:62 +/- 0:10 +/- 0:03 +/- 0:05) x 10(-3), B(D-s(+) -> eta pi(+)) = (17:41 +/- 0:18 +/- 0:27 +/- 0:54) x 10(-3), B(D-s(+) -> (K+Ks0)) = (15:02 +/- 0:10 +/- 0:27 +/- 0:47) x 10(-3), B(D-s(+) -> K-s(0)pi(+)) = (1:109 +/- 0:034 +/- 0:023 +/- 0:035) x 10(-3), B(D-s(+) -> K+pi(0)) = (0:748 +/- 0:049 +/- 0:018 +/- 0:023) x 10(-3), where the first uncertainties are statistical, the second are systematic, and the third are from external input branching fraction of the normalization mode D-s(+) -> K+K-pi(+). Precision of our measurements is significantly improved compared with that of the current world average values.