A measurement of the proton plus helium spectrum of cosmic rays in the TeV region with HAWC

TL;DR

This paper reports the measurement of the combined proton and helium cosmic ray spectrum in the TeV range using HAWC, revealing a spectral softening around 24 TeV with high statistical significance.

Contribution

First measurement of H+He cosmic ray spectrum in the TeV range with HAWC, including spectral features and composition separation techniques.

Findings

Detected a spectral softening at ~24 TeV with 4.1σ significance.

Reconstructed H+He spectrum from 6 to 158 TeV.

Used shower age and primary energy data to distinguish primaries.

Abstract

HAWC is an air-shower detector designed to study TeV gamma and cosmic rays. The observatory is composed of a $22000 \, m^2$ array of $300$ water Cherenkov tanks ($4.5 \, m$ deep x $7.3 \, m$ diameter) with $4$ photomultipliers (PMT) each. The instrument registers the number of hit PMTs, the timing information and the total charge at the PMTs during the event. From these data, shower observables such as the arrival direction, the core position at ground, the lateral age and the primary energy are estimated. In this work, we study the distribution of the shower age vs the primary energy of a sample of shower data collected by HAWC from June 2015 to June 2019 and employ a shower-age cut based on predictions of QGSJET-II-04 to separate a subsample of events dominated by H and He primaries. Using these data and a dedicated analysis, we reconstruct the cosmic ray spectrum of H+He from $6$ to $158$ TeV, which shows the presence of a softening at around $24$ TeV with a statistical significance of $4.1\sigma$.