Cosmic Ray Helium Energy Spectrum from Dark Matter Mission

Galactic cosmic rays (GCRs) are energetic particles traveling across the Galaxy as high-energy beams, and are a unique probe to explore the astrophysical particle accelerators and the interstellar medium of the Galaxy. The energy spectrum of GCRs is expected to be a power-law form for energies below the “knee” (at 3 − 4 PeV) according to the canonical shock acceleration of particles. However, several experiments surprisingly observed changes in the powerlaw spectral indices γ for protons, helium and heavy nuclei. Specifically, the spectra of GCRs become harder by ∆γ ‘ 0.1−0.2 at kinetic energies (or rigidities) of several hundred GeV/n (or GV), and become softer again by ∆γ ‘ −0.3 at energies of 15 − 30 TeV (for protons and possibly helium). The deviations from single power-law of the spectra motivate extensive investigations for deeper understanding of the acceleration and propagation mechanisms or of new possible GCR sources.

Precise measurements of the GCR spectra, particularly for individual species, are mainly from magnetic spectrometers such as the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA) and Alpha Magnetic Spectrometer (AMS-02) whose maximum measurable rigidity can reach only few TV. Direct measurements at higher energies were mostly done with balloon-borne calorimeter experiments in the past decades, and the uncertainties (both statistical and systematic) are somewhat large, hindering a good understanding of the spectral features above TeV energies.

The DArk Matter Particle Explorer (DAMPE) is a satellite-borne particle and γ-ray detector launched on December 17, 2015. It consists of a Plastic Scintillator Detector (PSD) for charge measurement, a Silicon Tungsten tracKer-converter (STK) for trajectory measurement, a Bi3Ge4O12 electromagnetic calorimeter (BGO) for energy measurement and electron-hadron discrimination, and a NeUtron Detector (NUD) for additional electron-hadron discrimination. DAMPE is expected to significantly improve the measurement precision of GCR spectra up to 100 TeV energies, due to its large acceptance and a good energy resolution.

The DAMPE data confirm the hardening feature of the helium spectrum reported by previous experiments. The hardening is smooth with a hardening energy of ∼1.3 TeV. The DAMPE data further reveals a softening feature at ∼34 TeV with a high significance of 4.3σ. Combined with the proton spectrum, the softening energy is well consistent with a dependence on particle charge, although a dependence on particle mass can not be ruled out yet. These results will provide important implications in understanding GCR acceleration or propagation processes. Extending the DAMPE measurements to even higher energies is possible with new data and improved analysis performance.

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of 4.3σ. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.

Arxiv – Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE
space mission

5 thoughts on “Cosmic Ray Helium Energy Spectrum from Dark Matter Mission”

  1. China is just wonderful isn't it? By all means we all want the longest running dictatorship to spring ahead with antigravity and teleportation that they will of course use to improve our lives (heavy sarcasm). If they aren't playing catch up then why do they continue to spy on our industry and steal billions of dollars worth of tech? And with the help of Google, Microsoft and other traitors they are helping fashion the new future of eternal monitoring from cradle to grave with A.I. capturing your every little imperfection. Yes, I should be jumping for joy at the great strides of wonderful peaceful China and the joyous singularity that they are helping create!

  2. Looking it up, "rigidity" in particle radiation is a function of charge, mass, and momentum, such that all particles of a given "rigidity" will have their paths bent to the same extent by a given magnetic field. I can see how it's a useful concept.

    Whereas hardness/softness of particle radiation is an old concept I was already familiar with, basically a measure of penetrating power: "Harder" radiation penetrates more shielding mass.

    Agreed, could have done without the CCP boosterism.

  3. Another nice contribution for humanity progress from China (yes this is chinese mission, detector)
    Why I am even wrtiting this? To point out how silly this famous concept that China can't innovate, can't do cutting edge science and tech is. China just needed some time to get to certain level, you can't expect advanced science/tech from country with less than $1000 per capita. You need to achieve certain level and China achieved it just recently(late 2010's). I don't expect largest space telescope or medicine breakthoughs from Nigeria, Ethiopia, Bangladesh, Myanmar or Indonesia soon.
    China is still catching up, developing, but we already see few cutting edge, original breakthroughs from China per week, soon they will achieve few per day, like we have in the West at this moment.

    It's a good thing, we will progress at faster rate and reach Singularity faster and Singularity level tech/science can keep you/us alive maybe even for thousands of years

    If we progress in slow pace(like now) because only few small places (relative to world population) are working on that (US, EU, Japan, Korea) we probably can't make it and will die. Everyone who don't want to die soon, should be rooting for China success and every other country ASAP progress in becoming developed because if all countries become rich and advanced and will be working on advanced science and tech, we(as human race) can progress 10-20x faster


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