Test of prototypes of the ALICE silicon pixel detector in a multi-track environment

The silicon pixel detector (SPD) comprises the two innermost layers of the ALICE Inner Tracking System (ITS). It is instrumented with arrays of hybrid pixels made out of 150 μm thick ASICs, each containing 8192 readout cells, bump bonded to 200 μm thick silicon sensors. The dimensions of the pixel cells are 50 μm (rϕ)×425 μm (z). Prototype assemblies have been tested in high-energy particle beams at the CERN SPS. The results of measurements in a multi-track environment, from interactions of an In beam at 158 AGeV on a Pb target, are reported.