Study of cluster reconstruction and track fitting algorithms for CGEM-IT at BESIII

Abstract

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 CGEM-IT: An Upgrade for the BESIII Experiment

“…A first, simplified digitization [70] does not consider the Lorentz angle nor the diffusion. The entrance and exit MC points in the drift gap are extracted from Geant4 simulation and the trajectory inside the gap is considered linear.…”

“…The second method, called Hough Track Finder [84], uses the whole tracking system at once, including CGEM-IT and ODC, and acts on all the hits in a global mode. Once the pattern recognition is completed, the track is fitted with the Kalman filter algorithm [70]. All these algorithms are validated with MC samples.…”

Track segment finding with CGEM-IT and matching to outer drift chamber tracks in the BESIII detector

“…There are two kinds of strips on the anode readout plane [4] which point to two different directions and are used to measure the induced charge from charged particles. The GEANT4-based [5] full simulation package was implemented for CGEM-IT which includes the detailed detector description and a simplified digitization [6]. The cluster reconstruction algorithm was developed, in which the continuous fired strips are reconstructed as clusters and the positions are calculated with the charge centroid method [6].…”

“…The GEANT4-based [5] full simulation package was implemented for CGEM-IT which includes the detailed detector description and a simplified digitization [6]. The cluster reconstruction algorithm was developed, in which the continuous fired strips are reconstructed as clusters and the positions are calculated with the charge centroid method [6]. The track fitting algorithm for Drift Chamber based on the Kalman Filter method [7] was also extended to incorporate both CGEM-IT clusters and Outer-Drift-Chamber (ODC) hits, so that the spatial and momentum resolu-tions can be studied for the tracks reconstructed within the tracking system of the CGEM-IT and the ODC [6].…”

“…A cluster reconstruction algorithm was developed, in which the continuous fired strips are reconstructed as clusters and the positions are calculated with the charge centroid method [6]. A track fitting algorithm for the drift chamber, based on the Kalman Fil-ter method [7], was also extended to incorporate both CGEM-IT clusters and outer drift chamber (ODC) hits, so that the spatial and momentum resolution can be studied for the tracks reconstructed within the tracking system of the CGEM-IT and the ODC [6]. This paper describes the track segment finding with CGEM-IT and the track matching between CGEM-IT and ODC.…”