The commissioning and operational experience of LHCb - Upstream Tracker

The LHCb detector has undergone a substantial upgrade, allowing the experiment to collect data with an all-software trigger, enabled by real-time front-end readout and rapid, efficient online reconstruction. The Upstream Tracker (UT), a four-plane silicon microstrip detector situated in front of the dipole magnet, is vital for reconstructing the paths of charged particles. The UT is crucial for tracking long-lived particles that decay outside the acceptance of the LHCb vertex detector, VELO. The UT was installed in LHCb in early 2023. The commissioning phase faced challenges due to data synchronisation issues associated with the read-out electronics. In this paper, we share lessons learned during the commissioning phase and operational experience from the first year of Run 3 data collection at LHCb, during which the performance of the UT was thoroughly examined.