Investigating the dark matter signal in the cosmic ray antiproton flux with the machine learning method

Abstract

We investigate the implications on the dark matter (DM) signal from the AMS-02 cosmic antiproton flux. Global fits to the data are performed under different propagation and hadronic interaction models. The uncertainties from the injection spectrum, propagation effects and solar modulation of the cosmic rays are taken into account comprehensively. Since we need to investigate extended parameter regions with multiple free parameters in the fit, the machine learning method is adopted to maintain a realistic time cost. We find all the effects considered in the fitting process interplay with each other, among which the hadronic interaction model is the most important factor affecting the result. In most hadronic interaction and CR propagation models no DM signal is found with significance larger than 2σ except that the EPOS-LHC interaction model requires a more than 3σ DM signal with DM mass around 1 TeV. For the diffusive reacceleration propagation model there is a highly significant DM signal with mass around 100 GeV. However, the signal becomes less than 1σ if we take a charge dependent solar modulation potential in the analysis. PACS numbers: 96.50.S-,95.35.+d arXiv:1903.09545v1 [astro-ph.HE]Cosmic ray (CR) antiproton is a very promising probe in the dark matter (DM) indirect detection. In recent years, a great progress of the measurement has been made by the AMS-02 experiment, which precisely measured the CRp/p ratio andp flux up to ∼ 450 GeV.Based on these results, lots of theoretical studies have been performed to investigate the possible contribution from DM in the antiproton flux [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. As the deviation between the expected secondary CR antiproton flux produced by the astrophysical processes and the data is not significant, any slight change of the background expectation could influence the DM implication. Therefore, the theoretical uncertainties of the secondary CR antiproton flux, mainly arising from the CR propagation process and the hadronic interactions between the CR particles and interstellar medium (ISM), are very important in the determination of the DM contribution.Although the principle of the strong interaction has been well described by the quantum chromodynamics (QCD), only the processes with large momentum transfers can be perturbatively calculated. The production processes of secondary CR antiprotons, which involve the forward scattering processes with multi-particle production, are always calculated under extra simplified assumptions or using some empirical parametrizations. This kind of processes has been a long time difficulty in the cosmic ray study. Many phenomenological models with different simplified assumptions have been constructed in the literature [19][20][21][22][23][24][25]. In addition, several empirical parametrizations only aiming to reproduce the antiproton production cross section have also been developed [26][27][28]. On the other hand, the CR propagation can be determined by the fit to the observed secondary-to-prim...

Dark matter or correlated errors: Systematics of the AMS-02 antiproton excess

“…Recently, several groups have reported an excess over the expected antiproton background in the rigidity range 10-20 GV in the AMS-02 data which is compatible with a dark-matter annihilation signal [6][7][8][9][10][11][12][13]. While the significance of the excess is highly controversial (ranging from 1−5 σ in the aforementioned studies), a common picture of the preferred dark-matter properties has emerged.…”

“…12 We have tested polynomial fits of lower and higher degree, but found that they do either not reproduce the shape of the data/MC correction function well or induce unphysical wiggles. 13 To perform a χ 2 fit, we have to assign an error in each rigidity bin shown in Fig. 3.…”

“…Of particular interest is the question how the correlations affect the interpretation of the antiproton excess at R = 10−20 GV. The latter has been considered as a possible dark matter signal in a number of studies [6][7][8][9][10][11][12][13]. At the same time, the significance of the excess is rather controversial (ranging from 1 to 5 σ within the mentioned references).…”

Pseudo-Goldstone dark matter confronts cosmic ray and collider anomalies

“…It has been analyzed by numerous groups who find an excess over the expected flux at energies of 10-20 GeV [22][23][24][25][26][27][28]. Intriguingly, this signal can be simultaneously explained with the GC gamma-ray excess by DM annihilating into bb [29][30][31]. In this paper we propose that both the GC and thep excesses can be explained by the annihilation of pseudo-Nambu Goldstone dark matter (pNGB DM).…”

Systematic uncertainties in the AMS-02 antiproton excess

“…In this article we present a systematical study of these two sources of uncertainties and investigate their impact on the significance of the above-mentioned DM signal and, hence, scrutinizing the robustness of this finding [8]. Meanwhile, similar analyses have also been carried out by other groups [9,10].…”