The CMS Trigger System

The CMS trigger system must reduce an input data rate from the LHC bunch-crossing frequency of 40 MHz to a rate which will be written to permanent storage. A detailed study has recently been made of the performance of this system. This paper presents key elements of the results obtained and gives details of a draft "trigger table" for the Level-1 Trigger and the High-Level Trigger selection at a "start-up" luminosity of 2 10^33 cm^-2 s^-1. High efficiencies for most physics objects are attainable with a selection that remains inclusive and avoids detailed toplogical or other requirements on the event.