A new inner tracker based on GEM detectors for the BES III experiment

Abstract

A new inner tracker based on a cylindrical gas electron-multiplier detector is under development to replace the current inner drift chamber of the BES III spectrometer. The BES III experiment is carried out at the BEPC II e[Formula: see text]e[Formula: see text] collider in Beijing at center-of-mass energies in the tau-charm region with a design luminosity of 1.0 [Formula: see text] 10[Formula: see text] cm[Formula: see text]s[Formula: see text]. The new inner tracker consists of three cylindrical layers of triple GEM surrounding the interaction point, covering 93% of solid angle. To fulfill physics requirements, a spatial resolution of 130 μm must be achieved. Both planar and cylindrical prototypes have been built and tested. A custom ASIC using UMC 110-nm technology has been designed to provide charge and time measurements—the first prototype is in testing. Notable and innovative aspects of the new inner tracker and the performance of the detector prototypes and readout ASIC are reported here.

Triple GEM performance in magnetic field

“…The mean value of one dimensional efficiency on the plateau region is above 98% and the spatial resolution is below 50 µm and depends mainly on the cluster hit multiplicity. The efficiency plateau begins at a gain of about 5000 as shown in figure 3a [18]. When a strong magnetic field orthogonal to the electron drift direction is applied the Lorentz force displaces the electronic cloud; the effect is a heavy smearing and deformation of the charge distribution shape at the anode.…”

MPGDs for tracking and Muon detection at future high energy physics colliders

“…Among the most prominent MPGD technologies, the Gas Electron Multiplier (GEM [6]) and Mi-croMegas (MM [7]) have been successfully operated in many different experiments, such as Compass [8], LHCb [9], TOTEM [10]. In addition, the low material budget and the flexibility of the base material makes MPGD suitable for the development of very light, full cylindrical fine tracking inner trackers at lepton colliders such as KLOE-2 [11] at DAFNE (Frascati, IT) and BESIII [12] at BEPCII (Beijing, CN).…”

“…In addition, the reduced impact in terms of material budget and the flexibility of the base material makes these devices suitable for the development of very light, full cylindrical fine tracking inner trackers at high luminosity tau-charm factories (STCF in Russia and SCTF in China). Among the most prominent MPGD technologies, the Gas Electron Multiplier (GEM, [6]) and MicroMegas (MM, [7]) have been successfully operated in many different experiments, such as Compass [8], LHCb [9], TOTEM [10], KLOE-2 [11], and are being built for the upgrades of ATLAS [15] and CMS [16] at LHC, and BESIII [12] at IHEP. The secret of the success of MPGDs, compared to classic gaseous detectors, lies in the sub-millimeter distances between the anodic and cathode electrodes.…”

“…Exploiting this feature a C-RWELL has been designed and it is under development, in the framework of the EU project CREMLINplus, as a low-mass inner tracker at the Super Charm-Tau Factory (SCTF) scheduled to be realized in Sarov (RU). In addition being designed as an "openable" and "modular" detector it will be a highly reliable and performing IT, while the spark suppression mechanism, intrinsic to the µ-RWELL technology, makes the operation of this detector more safe with respect to previous generation of cylindrical MPGD based devices, developed ten years ago in the framework of KLOE2 Collaboration [11], and successively by BESIII CGEM group [12]. Two ideas are under study, both based on a common double-faced cathode layout.…”

The CGEM-IT readout chain

“…The full system consists of about 10,000 electronics channels. Being a tracker, the first goal of the CGEM-IT is a precise position determination, with an expected resolution of 130 µm in 𝑟 𝜙 plane and 300 µm on the z coordinate, along the beam direction [6]. The main design goals are listed in table 3.…”