The ATLAS Level-1 Trigger: Status of the System and First Results from Cosmic-Ray Data

TL;DR

This paper describes the status and initial results of the ATLAS Level-1 trigger system at CERN, including cosmic-ray data analysis and system performance at early stages.

Contribution

It provides the first detailed overview of the Level-1 trigger system's implementation, status, and initial cosmic-ray data results at ATLAS.

Findings

First-level trigger reduces data rate by a factor of 10^4.

Cosmic-ray data analysis demonstrates system functionality.

Initial hardware performance aligns with design expectations.

Abstract

The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. At the design luminosity of 10^34 cm^-2 s^-1 there are on average 23 collisions per bunch crossing. A three-level trigger system will select potentially interesting events in order to reduce the read-out rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 10^4 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware.