Third Level Trigger for the Fluorescence Telescopes of the Pierre Auger Observatory

TL;DR

This paper presents a third-level trigger system for the Pierre Auger Observatory's fluorescence telescopes, significantly improving event selection efficiency and reducing false triggers through advanced hardware and software algorithms.

Contribution

Introduction of a novel third-stage trigger algorithm utilizing multiplicity signals for lightning rejection and space-time correlation for muon hit rejection, enhancing detection accuracy.

Findings

Lightning rejection efficiency above 99%

False rejection rate reduced by a factor of 10

Validated with measured and simulated showers

Abstract

The trigger system for the Auger fluorescence telescopes is implemented in hard- and software for an efficient selection of fluorescence light tracks induced by high-energy extensive air showers. The algorithm of the third stage uses the multiplicity signal of the hardware for fast rejection of lightning events with above 99% efficiency. In a second step direct muon hits in the camera and random triggers are rejected by analyzing the space-time correlation of the pixels. The trigger algorithm was tested with measured and simulated showers and implemented in the electronics of the fluorescence telescopes. A comparison to a prototype trigger without multiplicity shows the superiority of this approach, e.g. the false rejection rate is a factor 10 lower.