Monitoring radiation damage in the LHCb Silicon Tracker

The purpose of LHCb is to search for indirect evidence of new physics in decays of heavy hadrons. The LHCb detector is a single-arm forward spectrometer with precise silicon-strip detectors in the regions with highest particle occupancies. The non-uniform exposure of the LHCb sensors makes it an ideal laboratory to study radiation damage effects in silicon detectors. The LHCb Silicon Tracker is composed of an upstream tracker, the TT, and of the inner part of the downstream tracker (IT). Dedicated scans are regularly taken, which allow a precise measurement of the charge collection efficiency (CCE) and the calibration of the operational voltages. The measured evolution of the effective depletion voltage Vdepl is shown, and compared with the Hamburg model prediction. The magnitudes of the sensor leakage current are also analysed and compared to their expected evolution according to phenomenological models. Our results prove that both the TT and the IT will withstand normal operation until the end of the LHC Run II, after which they will be replaced in the context of the LHCb upgrade.