Speaker
Description
The cosmic ray all-particle energy spectrum exhibits a distinct softening at roughly $100 \, \rm PeV$, referred to as the second knee. This feature is widely regarded as signifying the cutoff of heavy Galactic nuclei and marking the onset of the Galactic-to-Extragalactic transition. Given the discrepancies in current experimental data regarding the second knee, the Large High Altitude Air Shower Observatory (LHAASO) is uniquely positioned to provide a definitive measurement. Based on the coincident detection of muons and electromagnetic particles at LHAASO, a robust energy reconstruction parameter $N_{\rm e \mu}^{\rm all}$ has been established, demonstrating its minimal sensitivity to primary composition and hadronic interaction models. This newly developed energy reconstruction method allows for an expanded effective area and a consequent increase in event statistics, while simultaneously mitigating saturation effects in electromagnetic particle detectors. Applying the aforementioned parameter to LHAASO-KM2A data, our preliminary analysis confirms the existence of the second knee and reveals a leveling-off trend in the mean logarithmic mass towards heavy nuclei beyond $100 \, \rm PeV$.
