The second knee observed in the local muon density spectra at various zenith angles

TL;DR

This study analyzes local muon density spectra at various zenith angles using data from NEVOD detectors, revealing a second knee in the spectra at around 10^17 eV, indicating a change in primary cosmic ray composition or interaction.

Contribution

It provides the first detailed observation of a second knee in LMDS at various zenith angles with increased statistical data from NEVOD detectors.

Findings

Identification of a second knee in LMDS at ~10^17 eV.

Increased data statistics compared to previous studies.

Slope of LMDS increases above 10^17 eV.

Abstract

Local muon density spectra (LMDS) at various zenith angles have been reconstructed from the data of two detectors of the Experimental complex NEVOD. The inclined muon bundles at the ground level were detected with the coordinate detector DECOR, and for the near-vertical direction with the calibration telescope system (CTS) of the Cherenkov water detector. In comparison with the earlier DECOR results, the experimental statistics has been increased by 2-3 times for different ranges of zenith angle and muon bundle multiplicity and is now based on about 40,000 h of the setup operation. The live time of measurements with CTS is about 12,000 h. It is found with both setups that the slope of LMDS is increasing above the primary energy of about 1017 eV. The details of the experiment and data analysis are presented.