Expectation on probing the origin of the cosmic ray knee with the LHAASO experiment

TL;DR

This paper evaluates LHAASO's capability to distinguish between different models of the cosmic ray knee by analyzing its ability to determine the dominant cosmic ray component in the 100 TeV to 10 PeV range.

Contribution

It demonstrates how LHAASO can discriminate between rigidity-dependent and mass-dependent models of the cosmic ray knee through composition measurements.

Findings

He-dominant knee under A-dependent model recognized at 6.6σ significance.

P-dominant knee under Z-dependent model identified at 2σ significance.

Heavier nuclei presence increases the significance of model discrimination.

Abstract

The cosmic-ray (CR) knee and the compositions contain abundant information for probing the CR's origin, acceleration and propagation mechanisms, as well as the frontier of the fundamental physics. Realizing that major proposals toward the knee's shape can be divided into two categories: the rigidity-dependent (also Z-dependent) knee and the mass-dependent (also A-dependent) knee, where the former one relates to the acceleration or the propagation mechanisms, and the other one is often associated with the new physics, it is essential to precisely measure the individual compositions. Benefit from the high altitude and hybrid detection methods, the LHAASO experiment has the ability in determining the individual component and brings us an opportunity in discriminating these two models. We test this expected ability of LHAASO from 100 TeV to 10 PeV with 3-year observation. And find the dominant component at the knee is essential to this issue, while much heavier nuclei occupying the knee leads to higher significance. In the analysis, the He-dominant knee under the A-dependent case can be recognized at the significance about 6.6 $\sigma$, while the P-dominant knee under the Z-dependent case will be classified with 2 $\sigma$ significance.