Last update: Apr 1, 2000
Speaker: Ralf GerhardsTESLA is one of the design proposals for a TeV range linear electron positron collider. It will, as proposed by the ECFA/DESY study group, collide electrons and positrons at center of mass energies of initially 500GeV at a luminosity of 3*10**34/cm**2/s. The incoming beams will collide in bunch trains with a rate of 5Hz and each train itself will consist of roughly 3000 bunches. The bunch to bunch distance within the train is in the order of 300ns resulting in a total train length of about 1ms. The expected physics rate is in the order of a few Hz.
This operation condition requires a deadtime free data taking within 1ms at a repetition rate of 5Hz. In conjunction with the aim of being able to select rare and maybe as yet unknown event topologies it gives rise for the proposal of a pure software trigger in the trigger concept of the proposed detector design.
The evolution of commercial off-the-shelf computing technologies (memories, fast networks and processors) is exploited as well. Rather than using a conventional multi-level trigger scheme with a purely hardware based first level, a single level software selection running on commodity hardware has been proposed. All detector signals are digitized and stored in buffers for each collision prior to event building through a fast network. All bunches are then analyzed in a processor farm and classified in various streams from interesting physics events to background, monitoring, and calibration events. Finally, all events are stored permanently in appropriate formats.
The clear advantages of this scheme are a deadtime-less readout, very good flexibility, because the full event information will be available for decision finding, and very good scalability. This selection strategy is very attractive for some classes of physics processes with unfavourable topologies as well as for the online analysis of background events for the machine group. According to first estimates, the event building process will have to cope with 1 to 2 Gigabytes of data per second. This number is not unrealistic to achieve, in particular in view of the corresponding values anticipated at LHC.
Presently, the compatibility of the trigger concept with the various subdetector designs is investigated and possible readout schemes are devised. The presentation will review the status of these studies, demonstrate the feasibility of the concept, and show how the evolution of the boundaries between online and offline processing could affect the overall computing model of future experiments.
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