The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider

TL;DR

This paper discusses the Muon Puzzle in cosmic-ray air showers, highlighting discrepancies between models and measurements, and explores potential explanations involving LHC data to improve understanding of hadronic interactions.

Contribution

It connects the Muon Puzzle to LHC observations, proposing that new effects observed at the LHC could explain the muon deficit in air shower models.

Findings

Significant muon deficit in air shower simulations compared to measurements

Discrepancy originates from secondary particle composition in hadronic interactions

Potential LHC effects could explain the muon puzzle

Abstract

High-energy cosmic rays are observed indirectly by detecting the extensive air showers initiated in Earth's atmosphere. The interpretation of these observations relies on accurate models of air shower physics, which is a challenge and an opportunity to test QCD under extreme conditions. Air showers are hadronic cascades, which eventually decay into muons. The muon number is a key observable to infer the mass composition of cosmic rays. Air shower simulations with state-of-the-art QCD models show a significant muon deficit with respect to measurements; this is called the Muon Puzzle. The origin of this discrepancy has been traced to the composition of secondary particles in hadronic interactions. The muon discrepancy starts at the TeV scale, which suggests that this change in hadron composition is observable at the Large Hadron Collider. An effect that can potentially explain the puzzle has been discovered at the LHC, but needs to be confirmed for forward produced hadrons with LHCb, and with future data on oxygen beams.