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Abstract: The recently reported positron fraction up to ∼350 GeV by AMS-02 seems to have tension with the total electron/positron spectra detected by Fermi and HESS, for either pulsar or dark matter annihilation/decay scenario as the primary positron sources. In this work we will show that the tension will be removed by an adjustment of the primary electron spectrum. If the primary electron spectrum becomes harder above ∼50 GeV, similar as the cosmic ray nuclei spectrum, the AMS-02 positron fraction and Fermi/HESS data can be well fitted by both the pulsar and dark matter models. This result may be suggestive of a common origin of the cosmic ray nuclei and the primary electrons. Furthermore, this study also implies that the properties of the extra sources derived from the fitting to the AMS-02 data should depend on the form of background. [Copyright &y& Elsevier]

Abstract: Recently, a tentative 130 GeV γ-ray line signal was identified by quite a few groups. If correct it would constitute a “smoking gun” for dark matter annihilations. Interestingly, the spectra of the cosmic ray electrons detected by PAMELA and Fermi-LAT both show tiny wiggle-like structure at ∼100 GeV, which might indicate a weak signal of the annihilation of ∼130 GeV dark matter particles into electrons/positrons with a velocity-weighted cross section . The prospect of identifying such a potential weak dark-matter-annihilation electron and/or positron component by AMS-02, a mission to measure the high energy cosmic ray spectra with unprecedented accuracy, is investigated. [Copyright &y& Elsevier]

A self-consistent global fitting method based on the Markov Chain Monte Carlo technique to study the dark matter (DM) property associated with the cosmic ray electron/positron excesses was developed in our previous work. In this work we further improve the previous study to include the hadronic branching ratio of DM annihilation/decay. The PAMELA $\bar{p}/p$ data are employed to constrain the hadronic branching ratio. We find that the 95% (2σ) upper limits of the quark branching ratio allowed by the PAMELA $\bar{p}/p$ data is ~0.032 for DM annihilation and ~0.044 for DM decay, respectively. This result shows that the DM coupling to pure leptons is indeed favored by the current data. Based on the global fitting results, we further study the neutrino emission from DM in the galactic center. Our predicted neutrino flux is some smaller than previous works since the constraint from γ-rays is involved. However, it is still capable to be detected by the forthcoming neutrino detector such as IceCube. The improved points of the present study compared with previous works include: (1) the DM parameters, both the particle physical ones and astrophysical ones, are derived in a global fitting way, (2) constraints from various species of data sets, including γ-rays and antiprotons are included, and (3) the expectation of neutrino emission is fully self-consistent. [ABSTRACT FROM AUTHOR]

Low energy cosmic rays are modulated by the solar activity when they propagation in the heliosphere, leading to ambiguities in understanding their acceleration at sources and propagation in the Milky Way. By means of the precise measurements of the e − , e + , e − + e + , and e + / (e − + e +) spectra by AMS-02 near the Earth, as well as the very low energy measurements of the e − + e + fluxes by Voyager-1 far away from the Sun, we derive the local interstellar spectra (LIS) of e − and e + components individually. Our method is based on a non-parametric description of the LIS of e − and e + and a force-field solar modulation model. We then obtain the evolution of the solar modulation parameters based on the derived LIS and the monthly fluxes of cosmic ray e − and e + measured by AMS-02. To better fit the monthly data, additional renormalization factors for e − and e + have been multiplied to the modulated fluxes. We find that the inferred solar modulation parameters of positrons are in good agreement with that of cosmic ray nuclei, and the time evolutions of the solar modulation parameters of electrons and positrons differ after the reversal of the heliosphere magnetic field polarity, which shows clearly the charge-sign dependent modulation effect. [ABSTRACT FROM AUTHOR]

The spatial-dependent-propagation (SDP) model with a nearby source works well to reproduce the coevolving features of both cosmic-ray (CR)-nuclei spectra and anisotropy. However, it is well known that the Sun is actually deviating from the galactic disk. This will lead to a dominating anisotropy in the direction perpendicular to the galactic disk, which is discrepant with current observations. Thus, it is necessary to further investigate the effect of the solar offset on anisotropy. In this work, to the best of our knowledge, this is the first time that the combined studies of the solar offset, nuclei spectra, and anisotropy have been performed based on the SDP model. As a result, to reproduce CR spectra and anisotropy, the thickness of the inner halo (Z I H) needs to increase linearly with the displacement of the Sun. We also know that the PeV anisotropy could be used to estimate the value of the diffusion coefficient, thus breaking the degeneracy between the diffusion coefficient and halo thickness. Therefore, it is a good approach to constrain the halo thickness. Moreover, the anisotropy in the PeV energy region, as a new probe, might also shed new light on constraining the solar offset. It is hoped that the anisotropy of the energies from ∼TeV to PeV can be finely measured with the LHAASO experiment, leading to a better understanding of the thick halo. [ABSTRACT FROM AUTHOR]

Galactic cosmic rays are mostly made up of energetic nuclei, with less than 1 % of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we develop an unsupervised machine learning method to identify electrons and positrons from cosmic ray protons for the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the supervised learning method used in the DAMPE experiment, this unsupervised method relies solely on real data except for the background estimation process. As a result, it could effectively reduce the uncertainties from simulations. For three energy ranges of electrons and positrons, 80–128 GeV, 350–700 GeV, and 2–5 TeV, the residual background fractions in the electron sample are found to be about (0.45 ± 0.02)%, (0.52 ± 0.04)%, and (10.55 ± 1.80)%, and the background rejection power is about (6.21 ± 0.03) × 10 4 , (9.03 ± 0.05) × 10 4 , and (3.06 ± 0.32) × 10 4 , respectively. This method gives a higher background rejection power in all energy ranges than the traditional morphological parameterization method and reaches comparable background rejection performance compared with supervised machine learning methods. [ABSTRACT FROM AUTHOR]

Abstract: In this work we study a class of leptophilic dark matter models, where the dark matter interacts with the standard model particles via the gauge boson, to explain the excess in cosmic rays observed by ATIC and PAMELA experiments, and more recently by Fermi experiment. There are three types of models: (a) , (b) , and (c) . Although ATIC or Fermi data are consistent with PAMELA data separately, ATIC and Fermi data do not agree with each other. We therefore aim to identify which of the three models can explain which data set better. We find that models (a) and (b) can give correct dark matter relic density and explain the ATIC and PAMELA data simultaneously recur to the Breit–Wigner enhancement. Whereas model (c) with a larger mass can explain Fermi and PAMELA data simultaneously. In all cases the model parameters are restricted to narrow regions. Future improved data will decide which set of data is correct and also help to decide the correct dark matter model. [Copyright &y& Elsevier]

Radiative energy losses are very important in regulating the cosmic ray electron and/or positron (CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina (KN) effect of the inverse Compton scattering (ICS) results in less efficient energy losses of high-energy electrons, which is expected to leave imprints on the propagated electron spectrum. It has been proposed that the hardening of CRE spectra around 50 GeV observed by Fermi-LAT, AMS-02, and DAMPE could be due to the KN effect. We show in this work that the transition from the Thomson regime to the KN regime of the ICS is actually quite smooth compared with the approximate treatment adopted in some previous works. As a result, the observed spectral hardening of CREs cannot be explained by the KN effect. It means that an additional hardening of the primary electrons spectrum is needed. We also provide a parameterized form for the accurate calculation of the ICS energy-loss rate in a wide energy range. [ABSTRACT FROM AUTHOR]

The Dark Matter Particle Explorer (DAMPE) is a satellite-borne detector designed to measure high energy cosmic-rays and γ -rays. As a key sub-detector of DAMPE, the Bismuth Germanium Oxide (BGO) imaging calorimeter is utilized to measure the particle energy with a high resolution. The nonlinear fluorescence response of BGO for large ionization energy deposition, known as the quenching effect, results in an under-estimate of the energy measurement for cosmic-ray nuclei. In this paper, various models are employed to characterize the BGO quenching factors obtained from the experimental data of DAMPE. Applying the proper quenching model in the detector simulation process, we investigate the tuned energy responses for various nuclei and compare the results based on two different simulation softwares, i.e. GEANT4 and FLUKA. The BGO quenching effect results in a decrease of the measured energy by approximately 2.5% (5.7%) for carbon (iron) at ∼ 10 GeV/n and < 1 % above 1 TeV/n, respectively. Accordingly, the correction of the BGO quenching effect leads to an increase of the low-energy flux measurement of cosmic-ray nuclei. [ABSTRACT FROM AUTHOR]

Abstract One of the main purposes of the DArk Matter Particle Explorer (DAMPE) is to measure the cosmic ray nuclei up to several tens of TeV or beyond, whose origin and propagation remains a hot topic in astrophysics. The Plastic Scintillator Detector (PSD) on top of DAMPE is designed to measure the charges of cosmic ray nuclei from H to Fe and serves as a veto detector for discriminating gamma-rays from charged particles. We propose in this paper a charge reconstruction procedure to optimize the PSD performance in charge measurement. Essentials of our approach, including track finding, alignment of PSD, light attenuation correction, quenching and equalization correction are described detailedly in this paper after a brief description of the structure and operational principle of the PSD. Our results show that the PSD works very well and almost all the elements in cosmic rays from H to Fe are clearly identified in the charge spectrum. [ABSTRACT FROM AUTHOR]

We propose a flavored U ( 1 ) e μ neutrino mass and dark matter (DM) model to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only the first two lepton generations of the Standard Model are charged under the new U ( 1 ) e μ gauge symmetry. A vector-like fermion ψ , which is our DM candidate, annihilates into e ± and μ ± via the new gauge boson Z ′ exchange and accounts for the DAMPE excess. We have found that the data favors a ψ mass around 1.5 TeV and a Z ′ mass around 2.6 TeV, which can potentially be probed by the next generation lepton colliders and DM direct detection experiments. [ABSTRACT FROM AUTHOR]

HERD is the High Energy cosmic-Radiation Detection instrument proposed to operate onboard China’s space station in the 2020s. It is designed to detect energetic cosmic ray nuclei, leptons and photons with a high energy resolution ( ∼1% for electrons and photons and 20% for nuclei) and a large geometry factor (>3 m 2  sr for electrons and diffuse photons and > [2]m 2  sr for nuclei). In this work we discuss the capability of HERD to detect monochromatic γ -ray lines, based on simulations of the detector performance. It is shown that HERD will be one of the most sensitive instruments for monochromatic γ -ray searches at energies between ∼ 10 to a few hundred GeV. Above hundreds of GeV, Cherenkov telescopes will be more sensitive due to their large effective area. As a specific example, we show that a good portion of the parameter space of a supersymmetric dark matter model can be probed with HERD. [ABSTRACT FROM AUTHOR]

The DArk Matter Particle Explorer (DAMPE) is a space-borne high energy cosmic-ray and γ -ray detector which operates smoothly since the launch on December 17, 2015. The bismuth germanium oxide (BGO) calorimeter is one of the key sub-detectors of DAMPE used for energy measurement and electron–proton identification. For events with total energy deposit higher than decades of TeV, the readouts of PMTs coupled on the BGO crystals would become saturated, which results in an underestimation of the energy measurement. Based on detailed simulations, we develop a correction method for the saturation effect according to the shower development topologies and energies measured by neighbouring BGO crystals. The verification with simulated and on-orbit events shows that this method can well reconstruct the energy deposit in the saturated BGO crystal. [ABSTRACT FROM AUTHOR]

Measuring high energy cosmic ray electrons/positrons (CRE) provides important means for the dark matter (DM) indirect detection and for probing the nearby galactic sources. In this work, we perform a systematic analysis of the flavor structure of DM annihilations into charged leptons based on the cosmic ray CRE spectra measured by DAMPE, Fermi-LAT, AMS-02, and CALET experiments. We study the annihilations of possible TeV scale DM particles in a nearby subhalo, which is proposed to explain the possible peak-like structure of the DAMPE CRE data. We pay special attention to the possible non-resonant excess (besides the possible peak-like structure) and demonstrate that such non-resonant excess can mainly arise from the decay of muons produced by the DM annihilations in the subhalo. With these we study the flavor composition of the lepton final states from DM annihilations χ χ → e + e − , μ + μ − , τ + τ − by fitting the CRE data. We demonstrate that decays of the final states μ + μ − and τ + τ − can provide the non-resonant excess, while the peak excess arises from the e + e − final state. We further analyze the constraints on the lepton flavor composition using the Fermi-LAT γ -ray measurements. We find that the flavor composition is consistent with the Fermi-LAT data at relatively low Galactic latitudes, while the fraction of the final state τ ± is severely bounded. [ABSTRACT FROM AUTHOR]