Energy spectra of cosmic-ray nuclei at high energies

TL;DR

This paper reports new high-energy measurements of cosmic-ray nuclei spectra, revealing similar spectral shapes across elements and a hardening in nitrogen spectrum at high energies, advancing understanding of cosmic-ray composition and acceleration.

Contribution

It provides the first detailed spectra of multiple cosmic-ray nuclei up to 10^14 eV and identifies a spectral hardening in nitrogen at high energies.

Findings

Spectral shapes of primary cosmic-ray nuclei are similar and follow an E^{-2.66} power law.

Nitrogen spectrum shows a clear hardening at energies above 100 GeV/n.

Measured N/O ratio at high energies aligns with previous results from CREAM.

Abstract

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to $\sim 10^{14}$ eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an $E^{-2.66 \pm 0.04}$ power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100-800 GeV/$n$ energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be $0.080 \pm 0.025 $(stat.)$ \pm 0.025 $(sys.) at $\sim $800 GeV/$n$, in good agreement with a recent result from the first CREAM flight.