The data-acquisition system for the CMS tracker beam tests

This paper describes the conception and the development of a real-time data -acquisition system for prototype detectors of the Tracker being designed f or the compact muon solenoid (CMS) experiment at the Large Hadron Collider of CERN, European Laboratory for Particle Physics, Geneva, Switzerland, The rationale for the development of a dedicated data-acquisition system was t he need to perform two fundamental beam tests (the "Milestone Barrel 1" and "Milestone Forward 1"), with large-scale prototypes of the detectors plann ed as the baseline design. The number of readout channels, the complexity o f the readout electronics, and the stringent requirements of the milestone tests mandated that a thorough understanding of the issues related to the p hysics of the detectors themselves be coupled with the application of leadi ng-edge electronic and software engineering technologies, The implementatio n described in this paper is based on a distributed architecture. An event builder CPU handles the two main tasks of synchronizing a variable number o f front-end processors and formatting the data in preparation for the trans fer to a dedicated high-performance storage system, while the front-end pro cessors handle the hardware and the real-time readout, Additional workstati ons are used to decouple the actual task of transferring the data files and monitoring the detector performance on-line fi om the readout farm. The sy stem has been successfully operated during the two aforementioned Milestone tests, allowing the CMS Tracker collaboration to pass them, with the simul taneous readout of up to 40 000 detector channels. The results of the two M ilestones have led to the compilation of the "Tracker Technical Design Repo rt", Subsequently,the same readout system has been used for a number of oth er beam tests, and it has formed the basis for the development of further, more advanced data-acquisition systems for the new readout electronic of th e CMS Tracker.