In particle physics, a trigger is a system that uses simple criteria to rapidly decide which events in a particle detector to keep when only a small fraction of the total can be recorded. Since experiments are typically searching for "interesting" events (such as decays of rare particles) that occur at a relatively low rate, trigger systems are used to identify the events that should be recorded for later analysis.

The aim of this presentation is to describe a new trigger for long-lived particles (LLPs) for ATLAS detector at CERN. The decay of long-lived particles is expected to produce unique signatures such as the production of trackless jets and, thanks to their specific properties, they can be selected and studied in a particle detector as the ATLAS one.