The CGEM-IT: An Upgrade for the BESIII Experiment

Abstract

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.

PARSIFAL: Parametrized simulation of triple-GEM and micro-RWELL response to a charged particle

“…The testbeam took place in the SPS North Area at CERN with a muon or pion beam with 150 GeV/c momentum. The detector configurations are described in Table 1 and the achieved results are reported in the literature [9][10][11].…”

Operation and readout of the CGEM inner tracker

“…The first two CGEM layers are manufactured in Italy and then shipped to Beijing where the final setup is assembled with the full gas system, HV distribution and readout chain [4][5][6]. The gas mixture chosen is Argon-Isobutane (90:10) for good electron diffusion properties and larger ionization.…”

TIGER/GEMROC: a versatile and modular readout system for micro-pattern gaseous detectors

“…The TIGER/GEMROC readout chain was developed to provide the Cylindrical GEM Inner Tracker (CGEM-IT) with a fast, modular readout system for the upgrade of the BESIII experiment at BEPCII [1]. Despite being designed for the typical signals produced by a GEM detector [2], the system is versatile enough to read other kinds of MPGDs having similar signal characteristics.…”