Operating conditions for the VELO silicon

The VELO detector, for the LHCb experiment at CERN, is foreseen to operate in an extreme radiation environment. This is a direct consequence of the requirement that the VELO sensors are placed close to the interaction point; in the current baseline design the sensors inner radius is 8mm (as measured radially) from the beam. Predictions of the bulk damage that will be received by these detectors have large uncertainties due to our state of knowledge of: cross-sections, parton distribution functions, beam related background, and of the residual neutron flux in the region of the VELO. Our best estimates, based on work presented in the Technical Proposal, and a recent simulation of the new VELO design, predict damage doses in the range 0.7 -- 1.3 × 10 14 1MeV neutrons/cm 2 /year at a radius of 1cm[1]. Below we present estimates, for non-oxygenated detectors, of the optimal operating temperatures and voltages for the sensors for irradiation doses between 2.1 and 3.9×10 14 1MeV neutrons/cm 2 /year, corresponding to a series of assumptions for a 3 years of LHC.