The Silicon Pixel Detector is...


..the innermost detector in ALICE, it will operate in a region where the track density could be as high as 50 tracks/cm2.

The SPD consists of two layers of silicon pixel detector modules located around the beam-pipe at an average distances of 39 mm and 76 mm from the beam axis, respectively.

SPD has a key role in the determination of the position of the primary vertex and in the measurement of the impact parameter of secondary tracks originating from the weak decays of strange, charm and beauty particles.

A unique feature of the SPD is its capability to generate a prompt trigger based on an internal fast-OR. Every 100 ns 1200 fast-OR signals are transmitted and processed in a separate processor unit according to a variety of pre-defined trigger algorithms to generate a signal that can contribute to Level 0 trigger decision in the ALICE central trigger processor (CTP) within about 800 ns from the interaction.

SPD mounted around the beam pipe


The Ladder


SPD sector

The basic components of the SPD are hybrid silicon pixels in the form of a two dimensional matrix of reversebiased silicon detector diodes . The detector element (the ladder) consists of a sensor matrix bump bonded to five readout chips. The single ladder matrix contains 256 x 32 cells measuring 50 µm (rφ) by 425 µm (z). All together the SPD contains 1200 readout pixel chips and a total of around 107 cells.