Measured air showers contain more muons than simulations with current hadronic interaction models predict

The verdict weighs three lines of evidence. First, the direct Auger line has strengthened: Auger's ground-level muon-signal excess over hadronic model predictions↗︎ is now verified on its own assessment, resting on three independent measurement lines (the 2016 hybrid fit with joint energy-scale rescaling, inclined showers, and AMIGA direct counting), with the magnitude qualifier made explicit: the inferred size depends on assumed composition and model shower-maximum scales, and Auger's 2024 template fit reduces the conservative excess to about 15 to 25 percent while retaining roughly five-sigma significance (Auger scientific highlight, www.auger.org/news/scientific-highlights/325-beyond-the-muon-puzzle). Together with the hybrid-data finding that larger hadronic signals are still required after shifting shower-maximum scales deeper↗︎, this establishes that mis-modelled composition alone cannot explain the discrepancy at the highest energies. Second, the WHISP nine-experiment combination↗︎ finds the excess growing with energy above 10 PeV at about eight standard deviations for the slope (arXiv:2001.07508; PoS ICRC2021 349; PoS ICRC2023 466), and the review by Albrecht et al. (arXiv:2105.06148) treats the excess as established. Third, against the claim, KASCADE-Grande, EAS-MSU, and Yakutsk data consistent with model predictions↗︎ show the excess is not universal; the WHISP reports note the combined significance depends on cross-experiment energy-scale calibration.

The status stays supported rather than verified because the general claim remains a synthesis across heterogeneous experiments with dominant systematic uncertainties, a minority of credible datasets sees no excess, and the magnitude has recently been revised downward, showing the measurement picture is still settling. It is supported rather than contested because existence at the highest energies is where the cross-experiment working group, the major collaborations, and the review literature all converge; the dispute now concerns magnitude and origin, not existence. Confidence rises from the previous pass because the strongest supporting line has been independently assessed as verified, with its magnitude caveat surviving an adversarial reading; credence 0.9 reflects that. What would change the conclusion: a demonstrated cross-calibration artifact in the WHISP combination, or retuned hadronic models (updated Sibyll or EPOS variants informed by LHC forward data) closing the gap against unchanged data, would push toward contested or contradicted; AugerPrime's separated muon measurements confirming the deficit at high significance across the energy range would push toward verified.