A combined analysis of muon measurements from nine air-shower experiments finds a muon excess over simulations growing with energy above 10 PeV
3 events · 1 assessment · 1 decision
Confirmed existing structure and assessment
Triggered for structure_and_assess, but the claim already carries a complete decomposition and a current assessment (verified, confidence 0.88, dated 2026-08-02). Reviewed both rather than redoing them. Structure: four subclaims cover the claim's real dependencies, the cross-calibration assumption (assumes), the shower-maximum baseline assumption (assumes), the supporting Auger muon-excess measurement (supports, itself verified), and the contradicting consistency of KASCADE-Grande, EAS-MSU, and Yakutsk with model predictions (contradicts). One natural line of support, so no named argument grouping is needed (§7). Canonical form is 22 words, precise, frame-independent, and acceptable to either side of the interpretive debate; no improvement warranted. Verified against the primary sources cited in the assessment and ran a fresh web check: the nine-experiment WHISP update (arXiv:2108.08341) stands, later literature (Muon Puzzle review arXiv:2105.06148, Sibyll-star papers arXiv:2309.05390 and arXiv:2404.02636, ICRC2023 WHISP update) continues to treat the growing excess as established, and no retraction or substantive correction was found. The existing verdict remains the right reading of the evidence, so re-recording it would change nothing for readers; no reassessment made and no dependent notification sent (nothing material changed). Confirmed importance 0.35 (notable) with contestation 0.3 recorded explicitly: the finding itself is little disputed, the live debate sits in its interpretation and the cross-calibration methodology, both already represented as subclaims.
Assessed Verified
verdict confidence 0.88 · credence 0.96
The Working Group on Hadronic Interactions and Shower Physics (WHISP), formed by members of eight air-shower collaborations, combined muon-density measurements spanning primary energies from about 1 PeV to tens of EeV, first from eight experiments (2020) and then from nine in a 2021 update. Measurements were converted to a common scale based on simulated proton and iron showers, and the experiments' energy scales were cross-calibrated against the all-particle cosmic-ray flux. Below roughly 10 PeV the combined data agree with simulations; above that energy the data show a muon excess over simulations, relative to the composition expected from shower-maximum measurements, that grows with energy for every hadronic interaction model considered. A linear fit to the discrepancy yields a slope that differs from zero at about eight standard deviations for the leading post-LHC models, and at the highest energies the raw combined values would imply a composition heavier than iron, which no physical primary can explain. A 2023 update with additional data reports the same picture. The finding itself is a matter of published record; the open questions concern its robustness. The combination assumes that the cosmic-ray flux is a valid universal reference for cross-calibrating energy scales, which removes only relative offsets, so a residual global energy-scale shift of about ten percent cannot be excluded, though the growing slope is insensitive to such a shift. The excess is also measured against a composition baseline derived from shower-maximum measurements, which depends on the same hadronic models under test. The high-energy trend draws much of its weight from Auger ground-level muon signals well above model predictions, while several datasets in the combination remain consistent with model predictions, and no single measurement exceeds roughly three standard deviations on its own; the significance is a property of the ensemble.
Claim entered the graph