2021 Fiscal Year Annual Research Report
Search for TeV-Range Dark Matter with Electron and Positron Cosmic Rays
Publicly Offered Research
| Project Area | What is dark matter? - Comprehensive study of the huge discovery space in dark matter |
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| Project/Area Number |
21H05463
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| Research Institution | Waseda University |
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Principal Investigator |
Motz Holger 早稲田大学, 理工学術院, 准教授(任期付) (30647904)
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| Project Period (FY) |
2021-09-10 – 2023-03-31
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| Keywords | Heavy Dark Matter / High Energy Cosmic Rays / CALET / AMS-02 / Supernova Remnants |
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| Outline of Annual Research Achievements |
As a first step, limits on Dark Matter (DM) annihilation and decay from a combined analysis of the latest all-electron spectrum measured by CALET [S. Torii, Y. Akaike et al. POS ICRC 2021 (105)] and the positron-only spectrum from AMS-02 [M. Aguilar et al. Phys. Rev. Lett. 122, 041102] have been calculated up to 100 TeV DM mass, using a parametrization of the astrophysical background based on a phenomenological broken power-law with cut-off model for the primary electron spectrum, and individual pulsar sources to model the positron excess.
The limits are calculated based on the reduction of this model's fit quality when adding the predicted flux from DM to the astrophysical background.
While this parametrization is suitable for lower DM mass, the heavy DM on which this project focuses, has its signal in the TeV region, where few nearby SNR are expected to dominate the spectrum. Therefore, as a first improvement, known nearby young SNRs (Vela, Cygnus Loop, Monogem) were added as individual sources. Instead of a constant energy loss term, the Klein-Nishina cross section is now used for a more precise cosmic-ray propagation calculation for the astrophysical sources.
Furthermore, the cosmic ray propagation models were improved optimizing their parameters in the numerical calculation with DRAGON in a random walk, finding a model explaining the measured nuclei spectra up to oxygen with a common injection spectrum for all nuclei, thus explaining the differences in the measured nuclei spectra by propagation effects only, without the need for species-specific acceleration mechanisms.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As outlined in the research plan, a main goal is to improve the dark matter limits by defining them based on a relative reduction of the fit quality to the pure astrophysical base model, instead of an absolute exclusion of the model. For this, the modelling of the astrophysical background is to be refined and the variation of the dark matter limits under variations of the background studied, to avoid reporting too strict limits due the uncertainty of the background.
The ingredients for this have now been assembled, refining the treatment of the individual astrophysical sources, but a systematic study of a large set of possible cases by randomizing the background source parameters is not yet done, as it requires significant computing resources and time.
To obtain intermediate results in a timely manner, limits based on the improved parametrization with only the nearby supernova remnants treated as individual sources (while keeping the phenomenological power law parallelization for the distant ones) are currently being calculated.
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| Strategy for Future Research Activity |
Further refinement of the used propagation model is ongoing, trying to also match the anti-proton spectrum in addition to the other nuclei spectra up to oxygen, as well as the nuclei up to iron/nickel. While many propagation parameters can be fixed based on the nuclei spectra, the magnetic field strength dominating the energy loss of electrons and thus the spectral shape of the dark matter signatures remains a mostly free parameter, for which a range of values should be studied in the dark matter limit calculations.
It is planned to replace the phenomenological broken power-law with cut-off model for the primary electron spectrum with randomly sampled SNR sources choosing samples fitting the data within χ2/ndof < 1. By taking take worst limit from many samples and thus considering many background scenarios, the relative limit definition could be considered sufficiently robust, giving stricter limits on the annihilation cross section or lifetime.
It was found that the calculation of limits on the flux from dark matter with the improved background modelling is computationally much more expensive, and simulating random SNR distributions naturally requires calculation of limits based on many samples. Therefore a large part of FY2022 funds will be invested in further computing capacity.
The publication of intermediate results at conferences is planned, while the paper publication of the final results is also contingent on the prior publication of an updated all-electron spectrum by the CALET collaboration.
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Research Products
(3 results)
