All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV

TL;DR

This paper presents the measurement of the all-particle cosmic ray energy spectrum from 10 to 500 TeV using the HAWC observatory, revealing a broken power law consistent with previous observations and bridging direct and ground-based detection methods.

Contribution

First measurement of the cosmic ray spectrum in this energy range with HAWC, demonstrating the detector's capability and providing new data bridging direct and ground-based observations.

Findings

Spectrum follows a broken power law with a break at ~45.7 TeV.

Measured spectral indices are -2.49 before and -2.71 after the break.

Results are consistent with previous measurements and validate detector performance.

Abstract

We report on the measurement of the all-particle cosmic ray energy spectrum with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range 10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to gamma rays and cosmic rays at TeV energies. The data used in this work were taken from 234 days between June 2016 to February 2017. The primary cosmic-ray energy is determined with a maximum likelihood approach using the particle density as a function of distance to the shower core. Introducing quality cuts to isolate events with shower cores landing on the array, the reconstructed energy distribution is unfolded iteratively. The measured all-particle spectrum is consistent with a broken power law with an index of $-2.49\pm0.01$ prior to a break at $(45.7\pm0.1$) TeV, followed by an index of $-2.71\pm0.01$. The spectrum also respresents a single measurement that spans the energy range between direct detection and ground based experiments. As a verification of the detector response, the energy scale and angular resolution are validated by observation of the cosmic ray Moon shadow's dependence on energy.