Measurement of the Cosmic Ray Helium Energy Spectrum from 70 GeV to 80 TeV with the DAMPE Space Mission

Abstract

Recent observations of the light component of the cosmic-ray spectrum have revealed unexpected features that motivate further and more precise measurements up to the highest energies. The Dark Matter Particle Explorer (DAMPE) is a satellite-based cosmic-ray experiment that is operational since December 2015, continuously collecting data on high-energy cosmic particles with very good statistics, energy resolution, and particle identification capabilities. In this work, the latest measurements of the energy spectrum of proton+helium in the energy range from 46 GeV to 316 TeV are presented. Among the most distinctive features of the spectrum, a spectral hardening at ∼600 GeV has been observed, along with a softening at ∼29 TeV measured with a 6.6σ significance. Moreover, by measuring the energy spectrum up to 316 TeV, a strong link is established between space-and ground-based experiments, also suggesting the presence of a second hardening at ∼150 TeV. * https://geant4.web.cern.ch/node/302 † https://web.ikp.kit.edu/rulrich/crmc.html

Measurement of the light component (p+He) energy spectrum with the DAMPE space mission

“…In order to unfold the detector response and hence compute the spectrum, we produced detailed Monte Carlo (MC) simulations of the DAMPE detector and of proton and helium CR events between 10 GeV and 500 TeV. These samples were simulated with the GEANT4 software, using the physics lists FTFP_BERT and EPOS-LHC (further details on this topic can be found in [8] and [9]).…”

“…Measurement of the light component (p+He) energy spectrum with DAMPE Francesca Alemanno helium spectra are also shown for comparison, with their respective systematic bands (for further details see [8] and [9]). The p+He spectrum shows a spectral hardening at ∼ 600 GeV and a softening at ∼ 25 TeV.…”

“…The standard paradigm of a single power-law cosmic-ray (CR) spectrum up to the knee energy (∼ PeV) seems to be not valid anymore, due to several results obtained with direct CR measurements. A first deviation from the single power-law, the so-called "hardening", has been observed at some hundreds of GeV/n from several experiments [1][2][3][4][5][6][7], in their measurements on hadronic spectra, along with a spectral softening found in the DAMPE proton [8] and helium [9] spectra, at ∼ 15 TeV and ∼ 34 TeV respectively. More measurements on these unexpected features are crucial in order to have a better understanding of CR acceleration and propagation mechanisms in our galaxy [10].…”

Charge measurement of cosmic rays by Plastic Scintillantor Detector of DAMPE

“…It consists of a Plastic Scintillator Detector (PSD) [2] for charge measurement, a Silicon Tungsten tracKer-converter (STK) [3] for trajectory measurement and γ-ray to e± conversion, a Bi 3 Ge 4 O 12 electromagnetic calorimeter (BGO) [4] for energy measurement and electron-hadron discrimination, and a NeUtron Detector (NUD) [5] for enhancement of electron-hadron discrimination. DAMPE is expected to significantly improve the measurement precision of galactic cosmic ray (GCR) spectra up to 100 TeV energies, due to its large acceptance and good energy resolution (∼1.5% for electrons and γ-rays [6] and ∼30% for nuclei [7,8]). Dedicated calibrations of each sub-detector show that the instrument works very stably on-orbit [9][10][11].…”

“…We quote light attenuation correction, geometrical alignment, and quenching-equalization [10,12,13]. All these corrections contributed to optimal charge resolution for proton and helium spectra measurement [7,8] and were based on light nuclei. DAMPE collected more 10 billions of high energy cosmic-rays until now, this huge sample enables us to calibrate the detector also for heavy nuclei.…”