The CGEM-IT: An Upgrade for the BESIII Experiment

The BESIII experiment has been collecting data since 2009 at the e+e− collider BEPCII in Beijing, a charm-τ 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

Operation and readout of the CGEM Inner Tracker

A recently approved ten-year extension of the BESIII experiment (IHEP, Beijing) motivated an upgrade program for both the accelerator and the detector. In particular, the current inner drift chamber is suffering from aging and the proposal is to replace it with a detector based on the cylindrical GEM technology. The CGEM inner tracker (CGEM-IT) consists of three coaxial layers of triple GEM. The tracker is expected to restore efficiency, improve z-determination and secondary vertex position reconstruction with a spatial resolution of 130 {\mu} m in the xy-plane and better than 300 {\mu} m along the beam direction. A dedicated readout system was developed. Signals from the detector strips are processed by TIGER, a custom 64-channel ASIC that provides an analog charge readout via a fully digital output up to about 50 fC, less than 3 ns jitter. TIGER continuously streams over-threshold data in trigger-less mode to an FPGA-based readout module, called GEM Read Out Card, that organizes the incoming data by building the event packets when the trigger arrives. Two of the three layers are in operation in Beijing since January 2020 remotely controlled. Due to the pandemic situation the integration activity has been continued on a small-scale prototype. Recently, a test beam has been performed at CERN with the final electronics configuration. In this presentation, the general status of the CGEM-IT project will be presented with a particular focus on the results from the test beam data acquisition.Comment: Prepared for the Vienna Conference on Instrumentation 202

The CGEM-IT: An Upgrade for the BESIII Experiment

The BESIII experiment has been collecting data since 2009 at the e+e− collider BEPCII in Beijing, a charm-τ 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

Cherenkov light imaging tests with state-of-the-art solid state photon counter for the CLAS12 RICH detector

A large area ring-imaging Cherenkov detector will be operated for hadron identification in the 3GeV/c to 8GeV/c momentum range at the CLAS12 experiment at the upgraded continuous electron beam accelerator facility of Jefferson Lab. The detector, consisting of aerogel radiator, composite mirrors and photon counters, will be built with a hybrid optics design to allow the detection of Cherenkov light for both forward and large angle hadron tracks. The active area has to be densely packed and highly segmented, covering about 1m2 with pixels of 6mm2, and to allow a time resolution of 1. ns. A technology that can offer a cost-effective solution and low material budget could be Silicon Photomultipliers (SiPM) thanks to their high gain at low bias voltage, fast timing, good single-photoelectron resolution and insensitivity to magnetic fields. An investigation is ongoing on samples of 3×3mm2 SiPM of different micro-cell size to assess the single photon detection capability in the presence of high dark count rate due to thermal generation effects, after-pulses or optical cross-talk and to study the response to the moderate radiation damage expected at CLAS12. In this work, a brief review of the latest and most interesting results from these studies will be shown

A Fit to the Available <i>e</i>⁺<i>e</i>⁻ → <inline-formula><math display="inline"><semantics><mrow><msubsup><mi mathvariant="sans-serif">Λ</mi><mi>c</mi><mo>+</mo></msubsup><msubsup><mover accent="true"><mi mathvariant="sans-serif">Λ</mi><mo>¯</mo></mover><mi>c</mi><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> Cross Section Data Nearby Production Threshold by Means of a Strong Correction to the Coulomb Enhancement Factor

There are two available sets of data on the e+e−→Λc+Λ¯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 ψ(4660), 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

Operation of the CGEM Detector

A ten years extension of the data taking of BESIII experiment, recently approved, motivated an upgrade program both for the leptonic collider BEPCII and for some of the sub-detectors of the spectrometer. BESIII is a multipurpose spectrometer optimized for physics in the charm-τ energy region. In particular, the current inner drift chamber is suffering from aging and the proposal is to replace it with a detector based on Cylindrical Gas Electron Multiplier (CGEM) technology to improve both the secondary vertex reconstruction and the radiation tolerance. The CGEM Inner Tracker will be composed of three coaxial layers of cylindrical triple GEMs, operating in an Ar + iC4H10 (90:10) gas mixture with field and gain optimized to maximize the spatial resolution. The new detector is readout with innovative TIGER electronics produced in 110 nm CMOS technology. A cosmic telescope instrumented with two out of three layers is in operation in Beijing since January 2020, remotely controlled by Italian groups due to the pandemic situation. A dedicated readout chain was developed for data acquisition. In this paper, the general status of the project will be presented with a particular focus on the preliminary results from the cosmic data taking and future plans