Measurement of the cosmic p+He energy spectrum from 50 GeV to 300 TeV with the DAMPE space mission

Recent observations of proton and helium in galactic cosmic rays (CRs) have revealed intriguing spectral features that motivate further direct measurements extending up to the multi-TeV energy region. Specifically, a first deviation (hardening) from the single power law describing the galactic CR spectrum has been found at hundreds of GeV, interpreted as a change in the diffusion coefficient. A second structure manifested by a spectral softening has been recently detected at tens of TeV although its origin remains unclear. Consequently, more measurements are needed in order to clarify the nature of such features. Current-generation space-based detectors are well-suited for performing the aforementioned measurements. Specifically, DAMPE (DArk Matter Particle Explorer) was designed to study galactic cosmic rays up to hundreds of TeV (among its various scientific objectives) with extremely good energy resolution and excellent particle identification capabilities. This thesis focuses on the spectral measurement of proton+helium in the energy range of 46 GeV to 316 TeV with the DAMPE detector. Combining proton and helium leads to increased statistics while maintaining an exceptional sample purity, as opposed to single proton or helium spectral measurements which are affected by cross-contamination and larger uncertainties at high energies (above 100 TeV). Moreover, the proton+helium measurement is also performed by ground-based experiments, although with large systematic uncertainties concerning the mass composition. Consequently, a direct measurement of the aforementioned spectrum from space will provide a bridge between experimental results obtained with diverse techniques. As a result of this work, a hardening feature at ∼600 GeV has been observed in the p+He spectrum, confirming previous direct observations. Then, at ∼26 TeV, a spectral softening has been found with an unprecedented significance of 6.7σ. This observation provides a valuable cross-check for the individual proton and helium analyses with increased statistics while minimizing possible contamination effects. Finally, by measuring the energy spectrum up to 316 TeV, a strong link is established between space- and ground-based experiments.