Commissioning of the ATLAS Electron and Photon Trigger Selection

TL;DR

This paper discusses the commissioning and performance evaluation of the ATLAS electron and photon trigger system during LHC startup, including comparisons between online and offline data and simulations.

Contribution

It provides an overview of the trigger system's commissioning process and performance, highlighting the initial online selection and tuning methods used for electron and photon triggers.

Findings

Successful commissioning of the trigger system

Good agreement between online and offline data

Effective trigger tuning based on simulations

Abstract

Since the start-up of the LHC end of 2009, the trigger commissioning is in full swing. The ATLAS trigger system is divided into three levels: the hardware-based first level trigger, and the software-based second level trigger and Event Filter, collectively referred to as the High Level Trigger (HLT). Initially, events have been selected online based on the Level-1 selections with the HLT algorithms run but not rejecting any events. This has been an important step in the commissioning of these triggers to ensure their correct functioning and subsequently to enable the HLT selections. Due to increasing LHC luminosity and the large QCD cross section, this has been a vital step to select leptons from J/$\Psi$, bottom, charm, W and Z decays. This presentation gives an overview of the trigger performance of the electron and photon selection. Comparisons of the online selection variables with the offline reconstruction are shown as well as comparisons of data with MC simulations on which the current selection tuning is performed.