Radiation Damage of LHCb's Silicon Detector Systems

The LHCb is a successful experiment taking data at the LHC since 2009. Vertex and track reconstruction in the regions with highest particle occupancies are performed with a set of micro silicon-strip detectors, consisting of the VErtex LOcator (VELO) and the Silicon Tracker (ST). The detectors have performed very well throughout Run 1 of the LHC, but face new operational challenges in the LHC Run 2 environment with the reduced bunch separation of 25 ns and higher particle multiplicities. The cumulative radiation damage poses challenges in reaching full depletion in the most irradiated zones of the detectors, which have highly non-uniform exposure, reaching fluences of 0.01-4×1014 1-MeV neq/cm2 in the same sensor. The overall damage is monitored through regular measurements of the leakage current and charge collection efficiency (CCE) as function of the bias voltage. The radiation damage has been shown to decrease the collection of signal by the strip implants due to charge accumulation in the SiO2 layer, reducing the shielding effect to the routing lines in the sensors with 2-metal layer readout. A TCAD simulation was implemented using the Perugia n-type bulk model and the Peltola surface damage model concluding that up to 60% of the charge is collected by the routing lines. Studies of radiation damage throughout runs 1 and 2 of the VELO and ST will be presented.