The Gigafitter: An online track fitting processor for CDF experiment and beyond

Real time event reconstruction plays a fundamental role in High Energy Physics experiments. The CDF experiment at the Tevatron collider performs a fast online reconstruction of high-resolution tracks using the Silicon Vertex Trigger (SVT). We will describe the architecture, the performance and the impact on CDF physics program of a next generation online track fitter, the GigaFitter, developed to improve the SVT track reconstruction efficiency as the Tevatron instantaneous luminosity increases. The core of the GigaFitter is implemented in a modern Xilinx Virtex-5 FPGA chip, rich in powerful DSP arrays. The higher computation power allows to perform many tasks in parallel, reducing the track parameter reconstruction to a few clock cycles: as a result, the GigaFitter can perform more than one fit per nanosecond. The Gigafitter installation and commissioning were successfully completed in February 2010: 12 Track Fitter boards, one per each azimuthal sector of the silicon detector, have been replaced by a single Gigafitter board receiving the data from the entire tracking detector. Besides being much more compact and robust than the previous system, the Gigafitter increases the SVT track reconstruction efficiency and acceptance and copes more effectively with the high-occupancy events that occur frequently at the high luminosities the Tevatron currently delivers. Moreover, its architecture is general enough to be adapted to different experimental environments: the experience gained with the Gigafitter upgrade will be essential for future SVT-like tracking processor such as FTK at Atlas experiment.