FOPI Trigger: Improving Statistics on Strange Particles

Introduction. FOPI experiments produce low statistics with respect to certain strange particles, especially negatively charged kaons [1]. The reasons are their rareness and the slow data read-out even with the updated FADC scanning system [2]. Thus, a trigger system is required to ensure that only events containing these particles are read by the FADC scanners [3]. We have investigated, how our trigger algorithm [4] can increase strange particle yield and how this affects hardware [5] requirements. Trigger Concept. The trigger will be integrated into the experiment as follows: the central drift chamber’s (CDC) sense wires signal is passed to the trigger via a discriminator, circumventing the FADCs. The trigger algorithm extracts the particles’ track information, and together with the time-of-flight data determines the particles’ species. If an anti-kaon is found the FADC scanners get a “start read-out” signal. If not, read-out time is saved. Performance. The first version of the trigger algorithm [4] was designed to classify – under optimal conditions – every particle contained in the CDC data. While this is the best way to analyze a single event, the procedure does not significantly increase the number of kaons that can be recorded during an experiment of fixed duration.