The BESIII experiment has been collecting data since 2009 at the e${}^{+}$e${}^{-}$ collider BEPCII in Beijing, a charm-$\tau$ factory characterized by high statistics and high precision. The discovery of exotic charmonium-like states and the still open questions in low-energy QCD led to an extension of the experimental program, with several upgrades. This review focuses on the CGEM-IT, the innovative solution proposed to replace the current inner tracker, which is aging. It consists of three, co-axial, cylindrical triple-GEM detectors and will be the first cylindrical GEM operating inside a 1 T magnetic field with analogue readout. For this purpose, a dedicated mixed-signal ASIC for the readout of CGEM-IT signals and FPGA-based electronics for data processing have been developed. The simultaneous measurement of both ionization charge and time distribution enables three reconstruction algorithms, to cope with the asymmetry of the electron avalanche in the magnetic field and with non-orthogonal incident tracks. The CGEM-IT will not only restore the design efficiency but also improve the secondary vertex reconstruction and the radiation tolerance. The gas mixture and gain settings were chosen to optimize the position resolution to ∼130 µm in the transverse plane and better than 350 µm along the beam direction. This paper addresses the innovative aspects in terms of construction, readout, and software, employed to achieve the design goals as well as the experimental measurements performed during the development and commissioning of the CGEM-IT.

The High-Luminosity phase of operation of the CERN LHC collider (HL-LHC) will pose new challenges to the detectors and their readout electronics. In particular, the CMS barrel electromagnetic calorimeter will require a full redesign of the electronic readout chain in order to cope with the increase in luminosity and trigger rate. In this framework, a new Application Specific Integrated Circuit (ASIC) integrating A/D conversion, lossless data compression and high speed transmission has been developed and tested. The ASIC, named LiTE-DTU, is designed in a commercial CMOS 65 nm process and embeds two 12-bit, 160 MS/s Analog to Digital Converters (ADCs), a data selection and compression logic, and a 1.28 Gb/s output serial link. The high-speed 1.28 GHz clock is generated internally from the 160 MHz input by a clock multiplication Phase-Locked Loop (PLL). The circuit has been designed implementing radiation tolerant techniques in order to work in the harsh environment of the HL-LHC upgrade. The LiTE-DTU is currently in the pre-production phase. A sample of 600 chips has been tested and incorporated into front end boards for systems performance testing.

There are two available sets of data on the $e^{+}{e}^{-}\to {\mathsf{\Lambda }}_c^{+}{\overline{\mathsf{\Lambda }}}_c^{-}$ cross section at energies close to the production threshold, collected by the Belle and by the BESIII Collaborations. The measurement of the former, performed by means of the initial state radiation technique, is compatible with the presence of a resonance, called $\psi \left(4660\right)$, observed also in other final states. On the contrary, the latter is measured an almost flat and hence non-resonant cross section in the energy region just above the production threshold, but the data stop before the possible rise in the cross section for the resonant production. We propose an effective model to describe the behavior of the data near this threshold, which is based on a Coulomb-like enhancement factor due to the strong interaction among the final state particles. In the framework of this model, it is possible to describe both datasets.

A search for C P violation with an entangled system of Ξ − Ξ ¯ + pairs is performed, using ( 10 , 087 ± 44 ) × 10 6 J / ψ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit e + e − → J / ψ → Ξ − Ξ ¯ + and its subsequent decays. The Ξ − and Ξ ¯ + decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, ( δ P − δ S ) = ( 0.3 ± 1.2 ± 0.2 ) × 10 − 2 rad , and the weak phase difference, ( ξ P − ξ S ) = ( − 0.2 ± 1.2 ± 0.1 ) × 10 − 2 rad , are directly determined. These are the most precise measurements to date. The C P asymmetry observables A C P Ξ = ( − 7.8 ± 4.8 ± 0.8 ) × 10 − 3 and Δ ϕ C P Ξ = ( 0.6 ± 5.1 ± 0.2 ) × 10 − 3 rad are determined, which are consistent with C P conservation. In addition, independent measurements of the Λ decay parameter and C P asymmetry A C P Λ = ( − 2.9 ± 4.3 ± 0.7 ) × 10 − 3 are also obtained, which are in agreement with the previous measurements, but with much improved precision.