Cosmic ray spectrum of protons plus helium nuclei between 6 TeV and 158 TeV from HAWC data

TL;DR

This study measures the cosmic ray spectrum of protons and helium nuclei between 6 and 158 TeV using HAWC data, revealing a spectral break at around 24 TeV with high statistical significance.

Contribution

It presents the first high-statistics measurement of the light cosmic ray spectrum in this energy range using Bayesian unfolding and mass separation techniques.

Findings

Identified a spectral break at ~24 TeV with 4.1 sigma significance.

Measured a spectral index change from -2.51 to -2.83 across the break.

Data is consistent with a broken power-law spectrum.

Abstract

A measurement with high statistics of the differential energy spectrum of light elements in cosmic rays, in particular, of primary H plus He nuclei, is reported. The spectrum is presented in the energy range from $6$ to $158$ TeV per nucleus. Data was collected with the High Altitude Water Cherenkov (HAWC) Observatory between June 2015 and June 2019. The analysis was based on a Bayesian unfolding procedure, which was applied on a subsample of vertical HAWC data that was enriched to $82\%$ of events induced by light nuclei. To achieve the mass separation, a cut on the lateral age of air shower data was set guided by predictions of CORSIKA/QGSJET-II-04 simulations. The measured spectrum is consistent with a broken power-law spectrum and shows a kneelike feature at around $E = 24.0^{+3.6}_{-3.1} $ TeV, with a spectral index $\gamma = -2.51 \pm 0.02$ before the break and with $\gamma = -2.83 \pm 0.02$ above it. The feature has a statistical significance of $4.1 \, \sigma$. Within systematic uncertainties, the significance of the spectral break is $0.8 \, \sigma$.