Why the knee at 100 PeV could not be seen?

TL;DR

The paper argues that the anticipated second knee in cosmic ray spectrum at 100 PeV is unlikely to be observed due to uncertainties in primary particle identification at lower energies.

Contribution

It clarifies the reasons why the expected iron knee at 100 PeV cannot be confidently identified based on current observations at 3-5 PeV.

Findings

The iron knee's position depends on primary composition interpretation.

Current data at 3-5 PeV do not conclusively identify the primary particles.

The absence of a clear iron knee challenges existing cosmic ray models.

Abstract

It is shown that a "second (iron) knee" in cosmic ray spectrum expected at energy about 100 PeV could not probably be found there. The reason is very simple: the position of the "iron knee" depends on an answer to the questions: "What do we see at 3-5 PeV? Is the knee seen at this energy associated with proton or iron primaries?"