Use of IT (current vs temperature) scans to study radiation damage in the LHCb VELO

This note describes the results of a study of radiation damage to the 88 silicon sensors of the VELO, using as input data the periodic current vs temperature (IT) scans. These scans enable the bulk current to be measured precisely and normalised to a given temperature. The change in current induced by radiation damage in the VELO sensors is compared to the one expected, using the temperature and fluence history in the sensors and the particle multiplicities predicted by the Monte Carlo, and found to be in good agreement. Measurements of the silicon effective band gag are determined from the IT scans at various levels of irradiation. After a delivered luminosity of 821pb$^{-1}$. the value is found to be $E_g$ = 1.13 $\pm$ 0.06 $\pm$ 0.04 eV.