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Doctoral thesis
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Measuring the Cosmic Ray Helium Flux with the DAMPE Experiment

ContributorsRuina, Arshia
DirectorsWu, Xin
Imprimatur date2023
Defense date2023
Abstract

The field of cosmic rays is still relatively new, compared to other sub-fields of physics, and is closely intertwined with the field of particle physics as well as astrophysics. Different methods (direct and indirect) probe different particles and energy regimes and form the puzzle pieces that when put together shall form our understanding of the nature of cosmic rays. Answering the questions that linger around the origins and the mechanisms of the propagation and acceleration of cosmic rays are an active field of research today.

Helium nuclei are the second-most abundant component in cosmic rays, after protons. Given their smaller interaction cross-sections (in other words, the prob- ability to interact) with the interstellar medium, as compared to heavier nuclei, they can travel larger distances, thereby becoming important probes to cosmic-ray sources as well as acceleration and propagation mechanisms. The DArk Matter Particle Explorer (DAMPE) is a satellite-borne detector in a Sun-synchronous orbit around the Earth at an altitude of ∼500km. The main scientific objectives of the experiment, which has been successfully collecting data for more than 7 years, are to measure cosmic-ray electrons, photons, protons, and heavier nuclei, and to perform indirect detection of Dark Matter. The detector system comprises a plastic scintillator detector (PSD) for charge measurement, a silicon-tungsten tracker-convertor (STK) for tracking incident particles, a bismuth germanium ox- ide (BGO) calorimeter for energy measurement, and a neutron detector (NUD) that further aids in lepton-hadron separation. More recently, deep-learning techniques were developed and deployed to improve particle tracking and identification, and to compensate for the energy lost in the calorimeter at high energies due to saturation of the electronics. This work presents a direct measurement of the energy spectra of cosmic-ray helium nuclei, using data collected over 81 months by DAMPE, from 70 GeV to 1 PeV. Applying the newly developed techniques helps extend the spectra to higher kinetic energies than those previously reported by DAMPE. Moreover, the results also confirm the presence of the hardening feature in the spectrum at 1.00 ± 0.20 TeV, as observed by previous experiments, as well as the softening feature at 25.56 ± 2.54 TeV, which was reported previously by DAMPE. Furthermore, a hint of a subsequent hardening is present at energies of a few hundreds of TeV.

Besides the cosmic-ray helium flux measurement, various calibrations and corrections that were made to the raw data (flight data) and to the Monte Carlo (MC) simulated data, are also presented in this thesis. One of them includes the correction of MC simulated data to account for low-energy back-scattering particles in DAMPE’s PSD. The other involves developing the so-called charge-loss correction for the STK. This correction is needed to factor in the bias generated in the charge measured by the silicon strips due to the impact position, angle of inclination and the size of the charge cluster from an incident CR particle.

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Citation (ISO format)
RUINA, Arshia. Measuring the Cosmic Ray Helium Flux with the DAMPE Experiment. 2023. doi: 10.13097/archive-ouverte/unige:170702
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Creation08/10/2023 7:08:54 AM
First validation08/16/2023 7:09:31 AM
Update time08/16/2023 7:09:31 AM
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