Speaker
Description
The LHCb detector is a single-arm forward spectrometer with precise silicon-strip detectors in the regions with highest particle occupancies. Around the interaction region, the VErtex LOcator (VELO) has active sensing elements as close as 8 mm from the LHC beams. The Silicon Tracker (ST) consists of a large-area detector located upstream of a dipole magnet, and three stations placed downstream of the magnet. Both detectors share the same front-end electronics, the Beetle chip.
The detectors performed very well throughout LHC Run-1 but new operating conditions for Run-2 pose new challenges. Signal spill-over from adjacent bunch crossings has to be considered in the reconstruction of clusters and tracks.
The non-uniform exposure of the LHCb sensors makes it an ideal laboratory to study radiation damage effects in silicon detectors. The VELO sensors are exposed to fluences of the order of $5\times10^{13}$ 1-MeV neq/cm$^2$ per $fb^{-1}$ while the ST sensor are exposed to more moderate fluences of the order of $10^{12}$ 1 MeV neq/cm$^2$ per $fb^{-1}$.
Several different methods are used to monitor the radiation damage. In
particular, regular High Voltage scans are taken which allow a precise
measurement of the charge collection efficiency (CCE) as function of the voltage.
This analysis is used to determine the operational voltages, and allows to monitor any degradation in the detector performance. In particular the radiation damage affects the cluster finding efficiency due to the double metal layer structure necessary to route the signal out to the FE electronics.
The overall performance of the VELO and ST during Run-2 will be presented.
The results of the latest high voltage scans will be shown, and measurements of the effective depletion voltage will be compared with the expected values that are calculated using the Hamburg model. The impact of these predictions are used to assess the operation of the detector during the remaining Run-2 data taking.
