The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 1/2 years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.

/pdf/measurement-of-the-cosmic-ray-proton-spectrum-from-40-gev-to-1bgbc741wi.pdf

Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

We report a measurement of the energy spectrum of cosmic rays for energies above 2.5×1018 eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above 5×1019 eV. The principal conclusions are(1) The flattening of the spectrum near 5×1018 eV, the so-called "ankle,"is confirmed.(2) The steepening of the spectrum at around 5×1019 eV is confirmed.(3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux (∝E-γ) changes from 2.51±0.03 (stat)±0.05 (syst) to 3.05±0.05 (stat)±0.10 (syst) before changing sharply to 5.1±0.3 (stat)±0.1 (syst) above 5×1019 eV.(4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above 8×1018 eV.

/pdf/measurement-of-the-cosmic-ray-energy-spectrum-above-2-5-1018-cm0y8tnr50.pdf

Measurement of the cosmic-ray energy spectrum above 2.5×1018 eV using the Pierre Auger Observatory

The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with two and a half years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time an experiment directly measures the cosmic ray protons up to ~100 TeV with a high statistics. The measured spectrum confirms the spectral hardening found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee, and sheds new light on the origin of Galactic cosmic rays.

Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite.

Future experiments based on the observation of Earth's atmosphere from sub-orbital and orbital altitudes plan to include optical Cherenkov cameras to observe extensive air showers produced by high-energy cosmic radiation via its interaction with both the Earth and its atmosphere. As discussed elsewhere [Phys. Rev. D 103, 043017 (2021); Phys. Rev. D 100, 063010 (2019)], particularly relevant is the case of upward-moving showers initiated by astrophysical neutrinos skimming and interacting in the Earth. The Cherenkov cameras, by looking above Earth's limb, can also detect cosmic rays with energies starting from less than a PeV up to the highest energies (tens of EeV). Using a customized computation scheme to determine the expected optical Cherenkov signal from these high-energy cosmic rays, we estimate the sensitivity and event rate for balloon-borne and satellite-based instruments, focusing our analysis on the Extreme Universe Space Observatory aboard a Super Pressure Balloon 2 (EUSO-SPB2) and the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) experiments. We find the expected event rates to be larger than hundreds of events per hour of experimental live time, enabling a promising overall test of the Cherenkov detection technique from sub-orbital and orbital altitudes as well as a guaranteed signal that can be used for understanding the response of the instruments.

Modeling the optical Cherenkov signals by cosmic ray extensive air showers directly observed from suborbital and orbital altitudes

The High Energy cosmic Radiation Detector (HERD) is a prominent space-borne instrument to be installed on-board the Chinese Space Station (CSS) around 2027, resulting from a collaboration among Chinese and European institutions. Primary scientific goals of HERD include: precise measurements of the cosmic ray (CR) energy spectra and mass composition at energies up to few PeV, electron/positron spectra up to tens of TeV, CR anisotropy, gamma ray astronomy and transient studies, along with indirect searches for Dark Matter candidates. The detector is configured to accept incident particles from both its top and four lateral sides. Owing to its pioneering design, more than one order of magnitude increase in geometric acceptance is foreseen, with respect to previous and ongoing experiments. HERD is conceived around a deep (∼55 X 0, 3 λ I ) 3D cubic calorimeter (CALO), forming an octagonal prism. Fiber Trackers (FiTs) are instrumented on all active sides, with a Plastic Scintillator Detector (PSD) covering the calorimeter and tracker. Ultimately, a Silicon Charge Detector (SCD) envelops the above-stated sub-detectors, while a Transition Radiation Detector (TRD) is instrumented on one of its lateral faces, for energy calibration in the TeV scale. This work illustrates HERD’s latest advancements and scientific objectives along with an overview of upcoming activities.

Overview of the HERD space mission

The search for the origin of cosmic rays is as active as ever, mainly driven by new insights provided by recent pieces of observation. Much effort is being channelled in putting the so-called supernova paradigm for the origin of galactic cosmic rays on firmer grounds, while at the highest energies we are trying to understand the observed cosmic-ray spectra and mass composition and relating them to potential sources of extragalactic cosmic rays. Interestingly, a topic that has acquired a dignity of its own is the investigation of the transition region between the galactic and extragalactic components, once associated with the ankle and now increasingly thought to be taking place at somewhat lower energies. Here, we summarize recent developments in the observation and understanding of galactic and extragalactic cosmic rays and we discuss the implications of such findings for the modelling of the transition between the two.

Selected Topics in Cosmic Ray Physics

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Selected Topics in Cosmic Ray Physics