Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

Abstract: A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.

• The paper demonstrates advanced detector simulation and reconstruction techniques that enhance ATLAS tracking and energy measurement capabilities.
• The paper outlines robust trigger algorithms and data handling strategies that efficiently filter rare events from high background noise.
• The paper reveals insights into ATLAS's physics potential by detailing multiple search channels for the Higgs boson and avenues for discovering new physics.

Overview of the Expected Performance of the ATLAS Experiment

The document under review is a comprehensive report on the expected performance of the ATLAS (A Toroidal LHC Apparatus) experiment at CERN, focusing on the detector, trigger, and delineating its physics potential. The ATLAS detector, a general-purpose apparatus, is a key component at the Large Hadron Collider (LHC), designed to explore the TeV mass scale, investigate electroweak symmetry-breaking, and probe physics beyond the Standard Model, including searches for the elusive Higgs boson.

Detector Performance

The ATLAS experiment depends critically on the functionality and performance of several subsystems, prominently the inner detector, the calorimeters, and the muon spectrometer. The report underscores advancements in detector simulation and reconstruction techniques that have been refined to handle and interpret collision data accurately.

Key performance metrics discussed include:

• Tracking: The inner detector is adept at reconstructing charged particle trajectories, benefiting from synergized utilization of pixel, silicon strip, and transition radiation technologies.
• Electron and Photon Detection: The electromagnetic calorimeter is instrumental in precise energy measurement and particle identification, crucial for accurate reconstructions in physics analyses.
• b-tagging: Identifying jets containing b-quarks with precision is critical for top quark and Higgs searches, leveraging advanced vertex reconstruction methods.

The document emphasizes the enhanced software frameworks developed for simulation, providing realistic scenarios to anticipate operational challenges and misalignments.

Physics Potential

The report intricately details the potential of ATLAS to discern various Standard Model processes and its capacity to usher in discoveries of new physics:

• Standard Model Processes: Analyses of minimum bias events and electroweak boson cross-sections are foundational for calibrations and systematics checks.
• Higgs Boson Searches: Multiple decay channels, including H → ZZ* → 4l and H → γγ, offer diverse avenues to pin down the Higgs, with statistical methods devised to combine results from different production and decay modes.
• Supersymmetry (SUSY) Searches: The report sheds light on the strategies to identify SUSY signatures, pivotal for extending the known particle framework.
• Exotic Phenomena: ATLAS also embarks on exploring high-mass dilepton resonances and leptoquarks, hinting at physics beyond the Standard Model.

Computational Efficiencies and Challenges

A section of the document is devoted to the computational steps and systematic uncertainties inherent in event reconstruction and analysis:

• Monte Carlo Simulations form the backbone for predictions, with varying orders of precision (LO, NLO, NNLO), providing cross sections for simulated processes.
• Triggering and Data Handling: The report discusses strategies for handling data quickly and efficiently through a sophisticated tiered trigger system that distinguishes rare physics events from the high background noise.

Implications and Future Trajectory

Practically, the ATLAS results in particle identification and measurement lay the groundwork for potentially discovering and understanding new particles and forces. Theoretical implications span interpretations of the fundamental forces and constituents of matter. The findings also foster speculations on the limitations and extensions of the Quantum Field Theories forming the edifice of modern high-energy physics.

In prospect, as actual experimental data supersedes simulations, continuous refinement in algorithms and calibration techniques will be pivotal. The ATLAS experiment stands as a towering achievement, offering boundless opportunities to unravel the intricacies of particle physics through collaborative ingenuity and technological prowess.

Overall, the document provides a meticulous guide to the anticipated capabilities of the ATLAS experiment, richly underscoring its instrumental role in pushing the frontiers of physics.