Triggering with the ALICE TRD

TL;DR

This paper presents a method for real-time triggering in the ALICE experiment at the LHC using the TRD, enabling rapid identification of high-pt particles and electron events for physics analyses.

Contribution

It introduces a novel on-line trigger system utilizing the ALICE TRD with fast reconstruction and calibration for efficient event selection.

Findings

Successful cosmic and pp run trigger performance tests

Implementation of real-time calibration for detector parameters

Capability to identify high-pt particles and electrons online

Abstract

We discuss how a level-1 trigger, about 8 us after a hadron-hadron collision, can be derived from the Transition Radiation Detector (TRD) in A Large Ion Collider Experiment (ALICE) at the LHC. Chamber-wise track segments from fast on-detector reconstruction are read out with position, angle and electron likelihood. In the Global Tracking Unit up to 6 tracklets from a particle traversing the detector layers are matched and used for the reconstruction of transverse momentum and electron identification. Such tracks form the basis for versatile and flexible trigger conditions, e.g. single high-pt hadron, single high-pt electron, di-electron (J/Psi, Upsilon) and at least n close high-pt tracks (jet). The need for low-latency on-line reconstruction poses challenges on the detector operation. The calibration for gain (pad-by-pad) and drift velocity must be applied already in the front-end electronics. Due to changes in pressure and gas composition an on-line monitoring and feedback loop for these parameters is required. First experiences on the performance were gathered from triggering in cosmic and pp runs.