Jul 4 – 11, 2012
Melbourne Convention and Exhibition Centre
Australia/Melbourne timezone
ICHEP2012 - 36th International Conference for High Energy Physics

The CMS High Level Trigger

Jul 6, 2012, 2:40 PM
Room 218 (Melbourne Convention and Exhibition Centre)

Room 218

Melbourne Convention and Exhibition Centre

Melbourne Australia
Parallel Sessions Track 13. Detectors and Computing for HEP Room 218 - Detectors and Computing for HEP - TR13


Dr Stéphanie Beauceron (Universite Claude Bernard-Lyon I (FR))


The CMS experiment has been designed with a 2-level trigger system: the Level 1 Trigger, implemented using FPGA and custom ASIC technology, and the High Level Trigger (HLT), implemented running a streamlined version of the CMS offline reconstruction software on a cluster of commercial rack-mounted computers, comprising thousands of CPUs. The design of a software trigger system requires a tradeoff between the complexity of the algorithms running online, the output rate, and the selection efficiency. The complexity is limited by the available computing power, while the rate is constrained by the offline storage and processing capabilities. The main challenge faces during 2012 is the fine-tuning and optimisation of the algorithms, in order to cope with the increasing LHC pile-up without impacting the physics performance. Here we will present a review of the performance of the main triggers uses during the 2012 data taking, ranging from simpler single-object selections to more complex algorithms combining different objects, and applying analysis-level reconstruction and selection. We will discuss how the increasing LHC pile-up is affecting their performance, and how these effects is being mitigated.

Primary author

Dr Stéphanie Beauceron (Universite Claude Bernard-Lyon I (FR))

Presentation materials