Speakers
Description
An upgrade of the inner tracker for the BESIII experiment has been completed in 2024. A three-layer Cylindrical GEM (CGEM) detector was installed in the BESIII detector, replacing the original inner drift chamber. For detector commissioning and alignment, cosmic-ray data were taken both with and without a magnetic field. A track reconstruction algorithm combing CGEM inner tracker (CGEM-IT) and outer drift chamber for cosmic-ray data analysis has been developed. In this algorithm, the Hough transform method is applied for the track reconstruction without magnetic field, while the Legendre transform method is used to reconstruct the track with magnetic field. Based on cosmic track reconstruction combing data with and without magnetic field, a preliminary alignment of the CGEM Inner Tracker using the Millepede method has been performed. Misalignment effect is reduced effectively after the alignment. This presentation will cover the track reconstruction procedure, the alignment strategy and preliminary validation with collision data.