Precise Measurement of the Cosmic-Ray Spectrum and 〈ln A〉 by LHAASO: Connecting the Galactic to the Extragalactic Components

Abstract Recently, the LHAASO Collaboration has provided precise measurements of the cosmic rays (CRs) all-particle energy spectrum and mean logarithmic mass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="〉" open="〈"> <mml:mrow> <mml:mi>ln</mml:mi> <mml:mi>A</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> from 0.3 to 30 PeV. Combining the CR measurements by AMS-02 and DAMPE in space and those by LHAASO and Auger on the ground, we construct a model to recover all these measurements from tens of GeV to tens of EeV. We find that the LHAASO measurement is crucial in the model construction by connecting the Galactic component to the extragalactic component. The precise measurements of CR spectra for individual species by AMS-02 and DAMPE together with the newest LHAASO results clearly indicate three Galactic CR components, that is, a soft low-energy background, a hard high-energy component, and a local source contribution. However, the LHAASO data show that above ∼10 16 eV, a nonnegligible extra component, possibly of extragalactic origin, must be included. Combining the Auger results and the LHAASO results, we figure out the extragalactic CRs that need at least two components at lower and higher energies. Thanks to the measurements by LHAASO, the constraints on the model parameters are quite stringent. The spectrum features and mass measurements in all energy ranges are all well reproduced in the model.