Project F4:
"Characterization of hadronic interactions using accelerator and air shower data"

Project Description

Hadronic interactions are crucial for understanding the universe at high energies, as they play a role every step along the long way from the cosmic ray sources to the signals in the detector. In project F4 we focus on the final step, namely the understanding of the cascades of hadronic interactions that occur when high-energy particles enter the atmosphere, so-called extensive air showers (EAS). The goal of project F4, together with F3, is to limit the extrapolation problem in the modeling of air showers by tuning the underlying hadronic interaction model simultaneously to measurements from high-energy physics (HEP) and EAS experiments.
During Phase 1, we developed and published a detailed strategy for tuning interaction models to HEP and astroparticle data, extended CORSIKA 8 to be able to use the event generator PYTHIA, performed first tunes to LHC, LEP, and low-energy fixed-target data, and demonstrated tuning to EAS data, albeit with simulations only. To further extend the energy range covered with LHC-precision measurements, we measured production ratios of strange hadrons with LHCb in fixed-target mode reaching down to 100 GeV energies.
In Phase 2, we focus on new HEP measurements from LHCb making use of the oxygen beams in Run 3 of the LHC, new muon data from Auger using the radio extensions for enhanced statistical precision, and finally, developing tools for automatic tuning, like a deep learning-based surrogate model for CORSIKA, to address the questions:

1. Do interaction models describe interactions of hadrons in the atmosphere accurately?
2. Are there contributions from new processes in high-energy interactions to the muon deficit, i.e. the lack of muons in simulated air showers compared to measurements?
3. Is it possible to consistently describe air-shower measurements and accelerator-based measurements using current models and can we adjust the current models to describe air showers, or do they need to be extended?