# Tracking axion-like particles at the LHC

## TL;DR

This paper proposes a novel LHC search strategy for highly boosted axion-like particles decaying into photon pairs, utilizing photon conversion to electron-positron pairs in the tracking detector to improve detection sensitivity.

## Contribution

The paper introduces a new method leveraging photon conversion in the tracker to distinguish collimated photon pairs from background, enhancing detection of axion-like particles in the MeV-GeV range.

## Key findings

- Potential to probe untested parameter space for ALPs
- Improved separation of collimated photons using tracking detector
- Enhanced sensitivity to ALPs produced via vector boson fusion

## Abstract

Highly boosted axion-like particles decaying into photon pairs are notoriously hard to detect at the LHC. The collimated decay photons cannot be individually reconstructed using only electromagnetic calorimeter information, making the signal less distinguishable from background. In this note we propose a search strategy to address this issue, exploiting the fact that a fraction of the decay photons convert into electron-positron pairs inside the tracking detector. The resulting tracks can be resolved with high resolution, allowing to separate the two collimated photons and resolve a displaced decay vertex. To demonstrate the effectiveness of this approach, we apply it to ALPs in the challenging MeV-GeV range produced via vector boson fusion. We find that such a search could give sensitivity to untested parameter space.