The Timepix3 Telescope and Sensor R&D; for the LHCb VELO Upgrade

The VErtex LOcator (VELO) of the LHCb detector is going to be replaced in the context of a major upgrade of the experiment planned for 2019-2020. The upgraded VELO is a silicon pixel detector, designed to withstand a radiation dose up to 8 × $10^{15}$1 MeV $n_{eq}$cm$^{−2}$, with the additional challenge of a highly nonuniform radiation exposure. A wide range of sensor prototypes has been tested in beam using the Timepix3 telescope to compare the key performance figures of the different prototypes. Detailed studies of the assemblies are performed using the precise particle tracking and timestamp information provided by the telescope. The performance of the Timepix3 telescope and the testbeam results are presented.