The CGEM-IT of the BESIII detector

BESIII is a spectrometer hosted at the leptonic collider BEPCII, at the Institute of High Energy Physics, in Beijing, since 2009. Its program covers charmonium(-like), charmed, and light hadrons spectroscopy, new physics, and QCD studies. The physics program has recently been extended up to 2030. In 2024, both the accelerator and the spectrometer underwent an upgrade program. The inner drift chamber, which was showing aging effects, has been replaced with a new inner tracker based on the cylindrical GEM technology. The CGEM-IT deploys three coaxial layers of cylindrical triple-GEM detectors. A dedicated electronic readout chain, based on the TIGER ASIC, and the FPGA-based GEMROC readout cards, has been thoroughly developed and tested with the final detectors. Studies with cosmic ray data taken during a standalone commissioning show a spatial resolution better than $200\,\mathrm{\mu m}$ with orthogonal tracks and a tracking efficiency of $95\%$ in each layer. The system was installed at the beginning of October 2024. This presentation will cover the project details, the results from the standalone commissioning with cosmic rays, and the most interesting parts of the installation.