The LHCb VELO: status and upgrade developments

The VErtex LOcator (VELO) is the silicon microstrip vertexing and triggering sub-detector of the LHCb experiment. It consists of a series of forward disks with the active region extending to just 8 mm from the LHC beams. The current status of the VELO is presented. Due to the high radiation environment, the VELO may have to be replaced after some years, possibly with new materials. A candidate material is Czochralski silicon. We present here promising new results on the first test beam of a large, high resistivity Czochralski microstrip silicon detector read out with LHC speed electronics. The performance was studied before and after irradiation with high energy protons. A signal to noise of over 20:1 was obtained from the detector and significant charge collection efficiencies were measured at relatively modest voltages after a fluence of 4.3×10¹⁴ 1 MeV neutron equivalents (n_eq) per cm². Studies using the Transient Current Technique probed the electric field within MCz test detectors and proved that MCz silicon does not type invert up until a radiation level of at least 5×10¹⁴ 24GeV/c p/cm². This would mean the VELO could possibly replace, in a potential upgrade, n⁺-on-n DOFZ sensors and the complicated processing involved, for standard p⁺-on-n processing with MCz.