The Performance of the ATLAS Trigger System in the LHC Proton-Proton Collisions

Abstract

In this paper we will report on the operation and the performance of the ATLAS data-flow system during the 2011 physics run of the Large Hadron Collider at 7 TeV. The data-flow system is responsible for reading out, formatting and conveying the event data, eventually saving the selected events into the mass storage. In 2010 the ATLAS Trigger and Data Acquisition system has been operated with an overall efficiency of 96%, while meeting evolving and demanding conditions. By the end of the proton run, the instantaneous peak luminosity had increased by 5 orders of magnitudes. Correspondingly, the ATLAS first-level trigger rate grew by a factor 100, reaching 40 kHz, roughly half of the design rate. Concurrently, the event building and data saving rates reached and exceeded the design performance. Moreover, the installation of additional computing power yielded a system whose characteristics are now comparable with the final ones. In this paper we report on achievements and problems encountered during 2010 and 2011. On this basis, we will follow discussing the preparations for the remaining 2011 data-taking period, in particular with respect to the expected increase in luminosity and the predicted reaching of the design first-level trigger rate.