Performance of the ATLAS Reconstruction Software with high level of Pileup in 2011

In 2011 the LHC provided excellent data, the integrated luminosity of about 5 fb−1 was more than what was expected. The price for this huge data set is the in- and out-of-time pileup, additional soft collisions overlaid on top of the interesting collision. 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 for all subdetectors is not applicable.