Investigating Production of TeV-scale Muons in Extensive Air Shower at 2400 Meters Underground

Abstract

The China Jinping Underground Laboratory, characterized by a vertical rock overburden of 2,400 m, provides an exceptionally effective shield against cosmic muons with energies below 3 TeV. The surviving high-energy muons, produced as part of extensive air showers, open a unique observational window into primary cosmic rays with energies ranging from tens of TeV up to the PeV scale and beyond. This distinctive feature also enables detailed studies of the earliest stages of shower development. Using 1,338.6 live days of data collected with a one-ton prototype detector for the Jinping Neutrino Experiment, we measured the underground muon flux originating from air showers. The results show discrepancies of about 40%, corresponding to a significance of more than 5.5$σ$, relative to predictions from several leading hadronic interaction models. We interpret these findings from two complementary perspectives: (i) by adopting the expected cosmic ray spectra, we constrain the modeling of the initial hadronic interactions in air showers; and (ii) by assuming specific hadronic interaction models, we infer the mass composition of cosmic rays, and our data favor a lighter component in the corresponding energy range. Our study demonstrates the potential of deep underground laboratories to provide new experimental insights into cosmic rays.

Figures (5)

• Figure 1: Schematic view of a TeV muon event observed with the one-ton prototype of JNE at CJPL.
• Figure 2: The surface energy distributions for muons arriving at CJPL-I, along with the CR total particle energy spectrum, as parameterized in Ref. Gaisser:2011klf. The hadronic model SIBYLL-2.3d is used here, accounting for EAS interactions. For comparison with primary CRs, the muon energy is multiplied by a factor, as discussed in Ref. Fedynitch:2018cbl.
• Figure 3: The comparisons of underground muon flux at CJPL-I between data and predictions based on post-LHC models at different zenith angles. In the top panel, the uncertainties from measurement points are plotted with error bars, while the uncertainties from predictions are shown with the dashed bands. In the bottom panel, both measurement and prediction uncertainties are combined and plotted with error bars.
• Figure 4: Comparisons of differential energy spectra for each muon contribution calculated with MCEq based on hadronic models. The GSF model is applied as the CR model, and the different zenith angles have been integrated here. In this figure, the black lines represent the total muon flux, while red, green, and blue lines show the muon fluxes from $\pi$, $K$, and prompt contributions, respectively. The dashed and point lines represent EPOS-LHC and QGSJET-II-04 models, respectively.
• Figure 5: The integral energy spectra for muons with energies above the threshold $E_{th}$. The red, blue, and green lines represent the results calculated from SIBYLL-2.3d, EPOS-LHC, and QGSJET-II-04, respectively. The solid lines represent the GSF model, while the dashed and dotted lines are derived by assuming CRs with pure components of protons and irons. The experimental measurements are plotted with error bars. Details are explained in the text.