HEP-Astro Seminar | The galaxy's history under our feet: paleo-detection of cosmic rays with PRimuS

The sources and history of cosmic rays are largely unknown because of the intrinsic deflection and delay imposed by cosmic magnetic fields. Minerals might offer a way to investigate this mystery from the rock record, as they preserve the damage tracks of the particles that crossed them over their geological history. This idea, known as paleo-detection, is mostly known for rare-event searches, such as WIMP recoils and neutrino interactions, where nanometre-scale tracks and the need for ultraclean minerals require a demanding readout. Cosmic rays are the opposite case: the signal is expected to be abundant, and the micron-to-tens-of-micron tracks can be revealed with simple etching and optical microscopy.

I will present the simulation framework we built to predict the track-length spectrum for a given mineral and flux history. It combines MCEq and Geant4, follows the overburden history of the sample, and folds in detection efficiency and measurement effects. I will then show how these predictions are confronted with data in PRImuS, our experimental proof of concept: chemical etching of obsidian, argon-plasma etching of halite, automated optical microscopy, and OptimusPrimus, a deep-learning tool for track recognition. The pipeline is validated on obsidian, and its application to halite is the next step. I will conclude with the outlook toward the possible GALACTIC project, based on light-sheet microscopy.