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Energy spectrum and mass composition of the primary cosmic rays based on the intensity of muon bundles detected in the NEVOD-DECOR experiment

A. G. Bogdanov, A. Chiavassa, D. M. Gromushkin, S. S. Khokhlov, V. V. Kindin, K. G. Kompaniets, A. Yu. Konovalova, K. I. Mannanova, G. Mannocchi, A. A. Petrukhin, G. Trinchero, I. Yu. Troshin, I. A. Shulzhenko, V. V. Shutenko, V. S. Vorobev, I. I. Yashin, E. A. Yurina

TL;DR

The paper presents a long-term analysis of inclined muon bundles detected by the NEVOD-DECOR setup (2 PeV to 3 EeV) using the Local Muon Density Spectra (LMDS) method to infer the primary cosmic-ray energy spectrum and mass composition. By coupling LMDS with CORSIKA-based muon LDFs across multiple hadronic models and two extreme primaries (p/Fe), the authors reconstruct all-particle spectra and track composition changes with energy, while highlighting strong dependence on hadronic modeling and assumption of the PCR spectrum. They find general agreement with light compositions at lower energies under several models but show that post-LHC models can conflict with LMDS at intermediate energies unless the primary flux is adjusted; at around $E_0\sim10^{18}$ eV, some models imply very heavy composition, while others favor lighter compositions, underscoring tensions in current hadronic understanding. The results emphasize the continued muon puzzle and motivate upgrades to NEVOD for extended energy reach and improved muon-counting capability to tighten constraints on hadronic-interaction models and CR mass composition.

Abstract

The results of the analysis of the NEVOD-DECOR data on the study of inclined muon bundles (with zenith angles from 40 to 85 degrees) of cosmic rays for the period from 2012 to 2023 are presented. An original method for studying the muon component of extensive air showers, local muon density spectra, was used. The data are compared with the calculations based on the simulation of air showers using the CORSIKA program for different models of hadronic interactions. The estimates of the energy spectrum and the behavior of the mass composition of primary cosmic rays in a wide energy range from 2 PeV to 3 EeV were obtained. They are compared with the data of other experiments.

Energy spectrum and mass composition of the primary cosmic rays based on the intensity of muon bundles detected in the NEVOD-DECOR experiment

TL;DR

The paper presents a long-term analysis of inclined muon bundles detected by the NEVOD-DECOR setup (2 PeV to 3 EeV) using the Local Muon Density Spectra (LMDS) method to infer the primary cosmic-ray energy spectrum and mass composition. By coupling LMDS with CORSIKA-based muon LDFs across multiple hadronic models and two extreme primaries (p/Fe), the authors reconstruct all-particle spectra and track composition changes with energy, while highlighting strong dependence on hadronic modeling and assumption of the PCR spectrum. They find general agreement with light compositions at lower energies under several models but show that post-LHC models can conflict with LMDS at intermediate energies unless the primary flux is adjusted; at around eV, some models imply very heavy composition, while others favor lighter compositions, underscoring tensions in current hadronic understanding. The results emphasize the continued muon puzzle and motivate upgrades to NEVOD for extended energy reach and improved muon-counting capability to tighten constraints on hadronic-interaction models and CR mass composition.

Abstract

The results of the analysis of the NEVOD-DECOR data on the study of inclined muon bundles (with zenith angles from 40 to 85 degrees) of cosmic rays for the period from 2012 to 2023 are presented. An original method for studying the muon component of extensive air showers, local muon density spectra, was used. The data are compared with the calculations based on the simulation of air showers using the CORSIKA program for different models of hadronic interactions. The estimates of the energy spectrum and the behavior of the mass composition of primary cosmic rays in a wide energy range from 2 PeV to 3 EeV were obtained. They are compared with the data of other experiments.

Paper Structure

This paper contains 10 sections, 9 equations, 19 figures, 3 tables.

Table of Contents

  1. Introduction
  2. NEVOD-DECOR setup
  3. Experimental data
  4. Data analysis (Local Muon Density Spectra)
  5. Observed LMDS
  6. Expected LMDS
  7. Comparison of observed and expected LMDS
  8. Estimates of the primary cosmic ray energy spectrum
  9. Behavior of the prinary cosmic ray mass composition
  10. Discussion and conclusions

Figures (19)

  • Figure 1: The quasi-spherical measuring modules of the detecting system of the Cherenkov water calorimeter NEVOD (left). The supermodules of the track detector DECOR mounted in one of the galleries of the laboratory building (right).
  • Figure 2: The example of a typical event with a muon bundle detected by the NEVOD-DECOR. The DECOR response (8 SMs in two projections) is shown in the top panel. The geometric reconstruction of the muon tracks in this event, as well as the scheme of the NEVOD-DECOR setup are shown in the bottom panel.
  • Figure 3: The examples of record-breaking multi-muon events detected by the NEVOD-DECOR setup (response of the detector DECOR is shown) with large zenith angles and large multiplicities.
  • Figure 4: The examples of geometric reconstruction of events with muon bundles selected in two sectors of azimuthal angles with a width of $60^{\circ}$ each. Figure shows the top view of the NEVOD-DECOR scheme.
  • Figure 5: The time dependence of the muon bundle counting rate of the NEVOD-DECOR (different series of data-taking are shown).
  • ...and 14 more figures