Conclusions: The Design of the ZEUS regional first level trigger box and associated trigger studies

Chapter 10


The performance of the ZEUS FLT has been investigated for a range of physics of interest, with special regard to the use of data from the tracking detectors. The motivation throughout this work has been to investigate the means by which signal events may be efficiently be selected by the trigger while at the same time holding leakage of beam-gas events through the trigger to a minimum. It has been shown that the RBOX will be able to successfully combine data from the FTD and the CTD in such a way as to further this aim despite the differing geometries of these two detectors.

The most important area of physics at HERA is the study of the proton structure function via the analysis of DIS NC and CC processes. An efficient trigger performance for these events is therefore essential. For this reason, the performance of the RBOX has been optimized with respect to them. The performance of the CTD alone for these events has been shown to be good which meant that it was difficult to further improve the situation. Nevertheless, it has been shown that the RBOX will be able to reduce the loss of CC events by a factor of two within the same beam-gas leakage constraints as placed on the CTD. This should greatly enhance the quality of measurements made.

While the performance of the RBOX has been shown to be good for DIS events, it is important not to lose sight of other areas of physics interest. With this in mind, other processes have been simulated with a view to examining performance in more broad terms. In particular, an investigation of heavy flavor pairs both with and without the influence of initial state gluon bremsstrahlung has been made. This has shown that transverse energy and charged multiplicity are the deciding factors which control the efficiency with which a type of event will be accepted. Also it has been shown that the effects of gluon bremmstrahlung may lead to significant changes in event characteristics for charmed pair events. Most importantly, it is now known that the RBOX will provide a good efficiency for heavy flavor events without the necessity to re-optimize the trigger parameters as designed for DIS.

Further, the efficiency of the RBOX for J/ψ events has been shown to be good. As was mentioned in the introductory chapter, these events will have a scattered electron at a very low angle. These two facts raise the prospect of using the electron calorimeter of the luminosity monitor to make precise measurements of the scattered electron which in turn will permit ZEUS to probe the gluon distribution in a kinematic domain which is completely inaccessible to other machines.

Accurate knowledge of a trigger efficiency is as important as boosting that efficiency. It has been shown here that the full kinematics of a CC event need not be considered when measuring the kinematic dependence of CTDFLT efficiency. This has allowed a picture to be constructed of the likely variation of efficiency which is comprehensive in terms of range. Also, much greater precision has been obtained than would be possible within available computer resources using another method.


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