Scrutinizing the evidence for dark matter in cosmic-ray antiprotons

Abstract

Global fits of primary and secondary cosmic-ray (CR) fluxes measured by AMS-02 have great potential to study CR propagation models and search for exotic sources of antimatter such as annihilating dark matter (DM). Previous studies of AMS-02 antiprotons revealed a possible hint for a DM signal which, however, could be affected by systematic uncertainties. To test the robustness of such a DM signal, in this work we systematically study two important sources of uncertainties: the antiproton production cross sections needed to calculate the source spectra of secondary antiprotons and the potential correlations in the experimental data, so far not provided by the AMS-02 Collaboration. To investigate the impact of cross-section uncertainties we perform global fits of CR spectra including a covariance matrix determined from nuclear cross-section measurements. As an alternative approach, we perform a joint fit to both the CR and cross-section data. The two methods agree and show that cross-section uncertainties have a small effect on the CR fits and on the significance of a potential DM signal, which we find to be at the level of 3σ. Correlations in the data can have a much larger impact. To illustrate this effect, we determine possible benchmark models for the correlations in a data-driven method. The inclusion of correlations strongly improves the constraints on the propagation model and, furthermore, enhances the significance of the DM signal up to above 5σ. Our analysis demonstrates the importance of providing the covariance of the experimental data, which is needed to fully exploit their potential.

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.…”

“…To this end, strong efforts have been made to improve the prediction and to quantify the uncertainties of antiproton production by cosmic-ray scattering [15][16][17][18][19]. The updated cross-section modeling entering the antiproton background was, indeed, found to somewhat reduce the antiproton excess [9][10][11]. However, one major piece was missing in all previous studies: the correlations of systematic errors in the AMS-02 data which have so far not been reported by the collaboration.…”

Fitting B/C cosmic-ray data in the AMS-02 era: a cookbook

“…Near the completion of this article, we found out that Cuoco et al (2019) also proposed to use a correlation matrix of errors to analyse AMS-02 data. However, while these authors focus on p and use a single correlation length fit on the data, our analysis relies on several correlations lengths whose values are motivated by physics processes in the AMS-02 detectors.…”

AMS-02 antiprotons' consistency with a secondary astrophysical origin

“…We underline that CRp's are one of the most sensitive astroparticle probes of annihilating/decaying DM in the GeV-TeV range [36][37][38][39][40], and any constraint on DM candidates depends on how well the astrophysical background is controlled. This is especially important as claims forp excesses attributed to DM are being debated [41][42][43][44][45].…”