Automatic Threshold Selection for BLM Signals during LHC Collimator Beam-Based Alignment

The Large Hadron Collider at CERN is the largest high-energy particle accelerator in the world. Proton beams are currently collided at an energy of 4 TeV per beam to investigate the fundamental elements of matter. The collider is equipped with a collimation system to ensure that potentially destructive halo particles are absorbed before they hit vulnerable elements. Beam-based alignment of the collimators is required to ensure that they are positioned for maximum cleaning efficiency. The alignment procedure relies on feedback from Beam Loss Monitors, and is currently being automated to speed it up. This paper describes a method for automatically selecting a threshold for the beam loss signal during alignment, based on an empirical analysis of collimator alignment data over one year of operation. The results achieved with threshold selection during alignments at 4 TeV are presented.