The “knee” of cosmic ray spectra may reflect the maximum energy accelerated by galactic cosmic ray sources or the limit of the galaxy’s ability to bind cosmic rays. Measurements of individual energy spectra are a crucial tool to understand the origin of the knee. Energy reconstruction and composition identification are foundations of the individual energy spectra measurements. One of the main scientific goals of Large High Altitude Air Shower Observatory (LHAASO) is measuring the cosmic ray energy spectra and composition from $\sim 10\mathrm{TeV}$ to $\sim \mathrm{EeV}$. In this work, a novel method for reconstructing energy and logarithm mass (lnA) based on a superposition model is introduced. Energy and lnA are reconstructed using two universal, composition- and energy-independent calibration lines. For zenith angle below 40 degree, the energy and lnA biases are within $\pm 5\%$ and $\pm 0.3$, respectively, across all compositions. The method uses particle densities—measured by LHAASO’s electromagnetic and muon detectors at a fixed distance from the shower axis—rather than integrated particle counts in annular bands. The density-based approach improves resolution for both energy and lnA, especially for heavy nuclei. The resulting energy resolution ranges from below 5% to $\sim 15\%$ above 1 PeV, the best mass resolution for iron achieved is below 25% above 10 PeV. The hadronic model dependencies of energy and lnA are also reported. These dependencies scale with lg($E/A$) and are nearly independent of primary composition.

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• Cosmic ray composition & spectra
• Cosmic ray & astroparticle detectors