The BABAR data acquisition system

The BABAR experiment at the Stanford Linear Accelerator Center is designed to perform a search for CP violation by analyzing the decays of a very large sample of B and B¯ mesons produced at the high luminosity PEP-II accelerator. The data acquisition system must cope with a sustained high event rate, while supporting real time feature extraction and data compression with minimal dead time. The BABAR data acquisition system is based around a common VME interface to the electronics read-out of the separate detector subsystems. Data from the front end electronics is read into commercial VME processors via a custom “Personality Card” and PCI interface. The commercial CPUs run the Tornado operating system to provide a platform for detector subsystem code to perform the necessary data processing. The data is read out via a non-blocking network switch to a farm of commercial UNIX processors. The current implementation of the BABAR data acquisition system has been shown to sustain a level 1 trigger rate of 1.3 kHz at an event size of 25 kbytes and with negligible deadtime. Upgrades currently in development will permit the system to support the design Level 1 rate of 2 kHz with negligible deadtime