Concept of a Software Trigger for an Experiment at the TESLA Linear Collider

TESLA is one of the design proposals for a TeV range linear electron positron collider. The electrons and positrons will collide in bunch trains with a rate of 5 Hz and each train itself will consist of 2820 bunches. The bunch to bunch distance within the train is 337 ns resulting in a total train length of about 1 ms. This operation mode requires a deadtime free data taking within 1 ms. In conjunction with the aim of being able to select rare and maybe as yet unknown event topologies it gives rise to the proposal of a pure software trigger concept in the proposed detector design. All detector signals are digitised and stored in buffers for each collision prior to event building via a fast network. All bunches are then analysed in a processor farm and classified in various streams from interesting physics to background, monitoring and calibration events. Finally, all events are stored in appropriate formats. According to first estimates, the event building process will have to cope with 1 to 2 Gigabytes of data per second. This value is an order of magnitude smaller then the corresponding rates anticipated at the LHC experiments. Presently, the compatibility of the trigger concept with the various subdetector designs is investigated and possible readout schemes are designed.