Measurement of attenuation length of the muon content in extensive air showers from 0.3 to 30 PeV with LHAASO

TL;DR

This study measures the attenuation length of the muon content in extensive air showers over 0.3–30 PeV using the LHAASO-KM2A detector with a model-independent constant intensity cut method. It finds Λ_mu increasing with shower energy, from about 449 to 811 g cm^{-2}, and compares results to three hadronic interaction models. The EPOS-LHC predictions align more closely with the data than QGSJET-II-04 or SIBYLL 2.3d, suggesting a preference for EPOS-LHC in describing high-energy hadronic interactions in air showers. The findings help constrain hadronic interaction models and improve understanding of muon production in EAS, with implications for cosmic-ray composition studies and high-energy atmospheric physics.

Abstract

The attenuation length of the muon content in extensive air showers provides important information regarding the generation and development of air showers. This information can be used not only to improve the description of such showers but also to test fundamental models of hadronic interactions. Using data from the LHAASO-KM2A experiment, the development of the muon content in high-energy air showers was studied. The attenuation length of muon content in the air showers was measured from experimental data in the energy range from 0.3 to 30 PeV using the constant intensity cut method. By comparing the attenuation length of the muon content with predictions from high-energy hadronic interaction models (QGSJET-II-04, SIBYLL 2.3d, and EPOS-LHC), it is evident that LHAASO results are significantly shorter than those predicted by the first two models (QGSJET-II-04 and SIBYLL 2.3d) but relatively close to those predicted by the third model (EPOS-LHC). Thus, the LHAASO data favor the EPOS-LHC model over the other two models. The three interaction models confirmed an increasing trend in the attenuation length as the cosmic-ray energy increases.

Figures (8)

• Figure 1: Layout of the KM2A full array. The red squares and blue dots indicate the EDs and MDs in operation, respectively. Showers are selected with reconstructed cores falling in the ring between the two black circles, featuring inner and outer radii of 320 and 420 m, respectively.
• Figure 2: Schematic of LHAASO-KM2A muon detector. One water tank is buried under 2.5 m of soil. The ultra-pure water within the tank reaches a depth of 1.2 m and is enclosed in a highly reflective bag.
• Figure 3: Left: Logarithmic number of muons distribution of one single MD unit ($N_{\mu\_u}$) after zenith angle correction for each zenith angle. The vertical dash line indicates the position of the single-muon peak and double-muon peak. Right: Fitting value of the logarithmic single-muon peak for each zenith angle; the error bar is smaller than the mark size.
• Figure 4: The distribution of the ratio between injected and measured number of muons across different zenith angles. The red line represents the result of linear fitting.
• Figure 5: The aperture of the KM2A full-array for cosmic-rays varies with the primary energy of different components. The selection criteria were $N_{e}$$\geq$ 80, shower core within 320-420 m, and 33.41$^\circ$$\leq$$\theta$$\leq$ 38$^{\circ}$.