Performance of the LHCb Vertex Locator

LHCb is a dedicated experiment to study new physics in the decays of beauty and charm hadrons at the Large Hadron Collider (LHC) at CERN. The beauty and charm hadrons are identified through their flight distance in the Vertex Locator (VELO), and hence the detector is essential for both the trigger and physics analyses. The VELO is the silicon micro- strip detector surrounding the LHCb interaction point, and is located only 8 mm from the LHC beam during normal operation. It consists of two retractable detector halves with 21 silicon micro-strip tracking modules each and is moved into position for each fill of the LHC, once stable beams are obtained. The detector operates in an extreme and highly non-uniform radiation environment, and the effects of surface and bulk radiation damage have already been measured. The VELO has been successfully operated for the first LHC physics run. Operational results show a signal to noise ratio of > 17 and a cluster finding efficiency of 99.5%. The small pitch and analogue readout, result in a best single hit precision of 4..m having been achieved at the optimal track angle. The VELO is the highest resolution vertex detector at the LHC.