As the main tracking detector of BESIII, the drift chamber provides accurate measurements of the position and the momentum of the charged particles produced in e + ecollisions at BEPCII. After six years of operation, the drift chamber is suffering from aging problems due to huge beam related background. The gains of the cells in the first ten layers show an obvious decrease, reaching a maximum decrease of about 29% for the first layer cells. Two calculation methods for the gain change (Bhabha events and accumulated charges with 0.3% aging ratio for inner chamber cells) give almost the same results. For the Malter effect encountered by the inner drift chamber in January 2012, about 0.2% water vapor was added to the MDC gas mixture to solve this cathode aging problem. These results provide an important reference for MDC operating high voltage settings and the upgrade of the inner drift chamber.

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A resistive anode for two-dimensional imaging detectors, which consists of a series of high resistivity pads surrounded by low resistivity strips, can provide good spatial resolution while reducing the number of electronics channels required. The optimization of this kind of anode has been studied by both numerical simulations and experimental tests. It is found that to obtain good detector performance, the resistance ratio of the pads to the strips should be larger than 5, the nonuniformity of the pad surface resistivity should be less than 20%, a smaller pad width leads to a smaller spatial resolution, and when the pad width is 6 mm, the spatial resolution (σ) can reach about 105 μm. Based on the study results, a 2-D GEM detector prototype with optimized resistive anode is constructed and a good imaging performance is achieved.

Considering the effects of aging on the existing Inner Drift Chamber (IDC) of BESIII, a GEM-based inner tracker, the Cylindrical-GEM Inner Tracker (CGEM-IT), is proposed to be designed and constructed as an upgrade candidate for the IDC. This paper introduces a full simulation package for the CGEM-IT with a simplified digitization model, and describes the development of software for cluster reconstruction and track fitting, using a track fitting algorithm based on the Kalman filter method. Preliminary results for the reconstruction algorithms which are obtained using a Monte Carlo sample of single muon events in the CGEM-IT, show that the CGEM-IT has comparable momentum resolution and transverse vertex resolution to the IDC, and a better z-direction resolution than the IDC.

The resistive anode readout facilitates a good spatial resolution with a large reduction of the electronics channels. The application of such readout method on a 100 × 100 mm 2 triple-GEM detector is presented. The detector anode covers 88 × 88 mm 2 sensitive area and consists of 11 × 11 resistive cells with the cell dimension of 8 × 8 mm 2 . The detector has been tested by using a 55 Fe source (5.9 keV) and an X-ray tube (8 keV). It is found that the spatial resolution (σ) is about 120 µm with the intrinsic detector response better than 100 µm. The position nonlinearity of the whole sensitive area is better than 3%. The energy resolution for 5.9 keV X rays is around 20% (FWHM) and the gain nonuniformity between different cells is better than 7%. The detector shows a quite good 2D imaging performance as well. Especially, the detector costs only half of the number of the electronics channels compared with that using the 2D strip readout. K: Electronic detector readout concepts (gas, liquid); Gaseous imaging and tracking detectors; Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc); X-ray detectors 1Corresponding author.