Beatenberg trigger workshop

25 February 2009

Courtesy of Gordon Watts.


At the heart of the Bernese Oberland, above lake Thun and in view of the spectacular Jungfrau group, sits the peaceful and relaxed village of Beatenberg (reputedly the longest village of Europe). This is where more than 140 ATLAS collaborators got together to address the fundamental questions of how to optimally exploit the experiment's trigger system as soon as the LHC will provide us with beam. Particular attention was devoted to the first transitional period when detector, Trigger-DAQ and physics commissioning of the experiment will be overlapping.

As the LHC repairs are advancing, the components of ATLAS are coming
back together to form a single experiment. This is true for the various sub-detectors, as well as the various groups of people involved in activities ranging from operation of the
experiment to physics analyses. The Beatenberg trigger workshop successfully gathered people from the ATLAS detector, trigger, performance and physics sub-communities in order to identify how the ATLAS trigger will be progressively used to effectively select events useful for detector and Trigger-DAQ understanding as well as physics analyses. This is an extremely sensitive topic for a hadronic experiment, which has implications on its most important resources: the detector health, the quality of the data collected and ultimately our ability to answer the questions for which the LHC and its experiments were built. It is not surprising therefore that the attendance to the workshop was strong and fruitful discussions were plentiful.

Much work was done over the previous weeks and months to prepare this workshop with the help of a panel of people with thorough experience in ATLAS and other experiments, and the outcome will be visible several months ahead. It is clear however that thanks to the Beatenberg gathering, we now have a rather complete view of what needs to be done. In order to facilitate the discussion, the all-plenary sessions were logically connected to cover the main areas of concern:

- Operations: how to operate the trigger in practice, what procedures should we follow to deploy changes in its configuration.
- Motivation: what reasons do we have for the various selection strategies that are the ingredients of the 'trigger menu'.
- Rate and resource measurement and management: what is the current knowledge of the bandwidth requirements of the various selections, as well as the tools and strategies that will allow us to diagnose and fix in real time bandwidth-related problems.
- Trigger evolution: how will the trigger strategy evolve through the LHC startup and all the way into data taking at different luminosity scenarios
- Trigger efficiencies: how will ATLAS determine and control the trigger (and analysis) efficiencies, and what reference samples do we need for these studies.

Some time will be needed to fully digest and follow up on all these topics, both within the communities and by individuals addressing specific issues. Many of the talks raised important issues and questions. These will be addressed in the future, keeping the larger ATLAS community informed through reports at the next ATLAS Weeks.

Overall we came back from Beatenberg with a better agreement and understanding of our start-up strategy and all the various grey areas which will need additional work and/or prompt response as soon as data will start flowing through ATLAS. The impeccable organization of the workshop, very wisely based for accommodation, meals and conference rooms in the same building, was possible thanks to the support of the University of Geneva. I am sure that all the participants are grateful to the colleagues that invested their time in the practical organization of this very successful event: William Bell, Andrew Hamilton, Szymon Gadomski, Phillip Urquijo, Francesca Bucci, Clemencia Mora Herrera, Anna Phan and Xin Wu.

A special get well note goes from all of us to our colleague Seth Caughron, who was unable to attend the workshop due to an unfortunate ski accident. We thank him in particular for having finished his talk before he went skiing!

 

 

 

Alex Cerri

CERN