Search Results (4)

The BESIII Collaboration has collected large data samples from $e^{+}{e}^{-}$ collisions at center-of-mass energies ranging from 1.84 to 4.95 GeV, which include the world’s largest charmonium sample, consisting of 10 billion $J/\psi$ and 3 billion $\psi \left(3686\right)$ events. These high-statistics datasets enable BESIII to carry out a wide range of studies in hyperon physics. In this article, we review the major achievements of the BESIII Collaboration in this field, which can be broadly categorized into four areas: hyperon polarization and $CP$ violation, rare hyperon decays, hyperon pair production, and hyperon–nucleon interactions. Full article

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. Full article

The charmonium-like exotic states $Y\left(4230\right)$ and the less known $Y\left(4320\right)$, produced in $e^{+}{e}^{-}$ collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and pion decay channels in the compact tetraquark scheme, with a method that proves to work equally well in the most studied $D^{\ast }\to \gamma /\pi +D$ decays. The decay of the vector Y into a pion and a $Z_c$ state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates are found to depend on the fifth power of pion momentum, which would make the final states $\pi Z_c\left(4020\right)$ strongly suppressed with respect to $\pi Z_c\left(3900\right)$. The agreement with BES III data would be improved considering the $\pi Z_c\left(4020\right)$ events to be fed by the tail of the $Y\left(4320\right)$ resonance under the $Y\left(4230\right)$. These results should renovate the interest in further clarifying the emerging experimental picture in this mass region. Full article

We analyze possible singularities in the $J/\psi \Lambda$ invariant mass distribution of the ${\Xi }_b^{-}\to K^{-}J/\psi \Lambda$ process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with ${\Xi }^{*}$-charmonium-$\Lambda$ intermediate states, the one from the ${\chi }_{c1}\Xi \left(2120\right)\Lambda$ loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs S- and P-waves in ${\chi }_{c1}\Lambda$ and $J/\psi \Lambda$ systems, respectively, when the quantum numbers of these systems are $1/2^{+}$ or $3/2^{+}$. When the quantum numbers of the $\Xi \left(2120\right)$ are $J^P=1/2^{+}$, $1/2^{-}$ or $3/2^{+}$, the peak structure should be sharper than the other $J^P$ choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the ${\Xi }^{*}$-charmonium-$\Lambda$ triangle diagram if structures are observed in the $J/\psi \Lambda$ invariant mass spectrum experimentally. In addition, a few triangle diagrams with the $D_{s1}^{*}\left(2700\right)$ as one of the intermediate particles can also produce singularities in the $J/\psi \Lambda$ distribution, but at higher energies above 4.9 GeV. Full article