Radiation damage effects in the NA60 silicon pixel detectors

The NA60 experiment studies open charm and prompt dimuon production in proton–nucleus and nucleus–nucleus collisions at the CERN SPS. Downstream of the target system a silicon pixel telescope made with p-on-n silicon sensors measures the charged tracks originating from the collisions. During the 2003 data taking period with indium–indium collisions a significant radiation dose was collected. Simulations done before the run predicted a fluence of up to several in the most affected regions of the sensors and a difference of approximately a factor ten between the inner and outer regions of certain sensor chips. The inhomogeneous distribution of the fluence leads to type inversion in some regions of the sensors while other regions of the same sensors kept their initial behaviour. The depletion voltages and leakage currents were measured during the run and have been compared with the estimates we had previously made. This paper shows simulation results of fluence and radiation damage and comparisons with the measurements performed throughout the data taking period.