Rolf Seuster (Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut))
In 2011 the LHC provided excellent data, the integrated luminosity of about 5fb-1 was more than what was expected. The price for this huge data set is the in and out of time pileup, additional soft events overlaid on top of the interesting event. The reconstruction software is very sensitive to these additional particles in the event, as the reconstruction time increases due to increased combinatorics. During the running of the experiment in 2011, several successful changes to the software were made that sped up the reconstruction. Pileup has different effects on the various detector technologies used in ATLAS and a general recipe is not applicable.
Collaboration Atlas (Atlas)