Filtering hits for speeding up online track reconstruction at hadron colliders

Abstract

Collider experiments are equipped with trigger systems that rapidly inspect the physics content emerging from collisions to decide whether the resulting products are worth saving for later analysis. One crucial aspect for analyzing the final states originating from the collisions is to process the information produced by charged particles in the innermost detectors to reconstruct the corresponding trajectories. This task is a challenge for the experiments running at the Large Hadron Collider (LHC) at CERN because of the large number of secondary collisions per bunch crossing, the so-called pile-up vertices, giving rise to extremely high hit occupancies in the detector layers close to the beam line. Reconstructing tracks is a combinatorial problem and its processing time strongly depends on the average pile-up per event. The future accelerator-complex upgrade to the High-Luminosity LHC, implying even higher detector occupancies, will result in a considerable growth of the computational cost of the current trigger strategies. To face this issue, a new technique for assisting track reconstruction by filtering out unnecessary detector information is presented and characterized in this work. The algorithm is based on a convolutional-neural-network architecture which can be easily deployed on accelerator cards. The impact of this approach is assessed and future prospects are also discussed.