Study Explains Nonlinear Temperature Dependence of Underground Muon Rates at Daya Bay Neutrino Experiment
Researchers at the Daya Bay Neutrino Experiment have identified and theoretically explained a nonlinear dependence of underground cosmic-ray muon rates on atmospheric temperature, a departure from predictions of established theories. Existing models by Barrett, Gaisser, and others account only for local temperature effects at the muon production layer, neglecting the influence of the full atmospheric temperature profile. The new, more general solution to the cascade equations recovers a linear modulation when the entire profile is considered, offering a refined framework applicable to other experiments worldwide.
Underground cosmic-ray muon rates are well known to vary with atmospheric temperature, a phenomenon historically described by theories developed by Barrett, Gaisser, and colleagues. However, data from the Daya Bay Neutrino Experiment in China revealed that this dependence is nonlinear, which existing theoretical frameworks could not adequately explain. Researchers traced the discrepancy to a key simplification in prior work: those theories consider only the local temperature at the altitude where muons are produced, ignoring how the broader vertical temperature profile shapes the final muon flux at ground level. The new study derives a more general solution to the atmospheric cascade equations, introducing updated definitions of effective temperature weight and temperature coefficient that account for the full profile. Validation using the numerical tool MCEq with real atmospheric temperature inputs successfully recovered a linear modulation, confirming the theoretical approach. The authors argue their framework resolves the nonlinear anomaly observed at Daya Bay and provides a more accurate calculation method for temperature coefficients at other underground detectors. The preprint, comprising 14 pages and 7 figures, was submitted to arXiv on June 8, 2026.
What's missing
The paper is a preprint and has not yet undergone peer review, so its results and conclusions have not been independently validated by journal referees. Additionally, potential systematic uncertainties in the real atmospheric temperature inputs used for MCEq validation are not detailed in the abstract.
What different sources said
- arXiv astro-phCenter
On the Nonlinear Dependence of Underground Muon Rate on Atmospheric Temperature Observed at Daya Bay
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