Scrutinizing the impact of the solar modulation on AMS-02 antiproton excess

TL;DR

This paper investigates how different solar modulation models affect the interpretation of AMS-02 antiproton data, revealing that the significance of potential dark matter signals varies with the model and uncertainty treatment.

Contribution

It compares three solar modulation models and evaluates systematic uncertainties, highlighting their impact on dark matter signal significance in AMS-02 antiproton observations.

Findings

DM signal significance varies with the modulation model used.

The force-field approximation yields a 2σ to 4σ significance for dark matter.

Systematic uncertainty treatment methods influence the fit quality and interpretation.

Abstract

This study examines the impact of solar modulation on the antiproton excess observed by AMS-02, which may indicate dark matter (DM) annihilation. We analyze three solar modulation models: the force-field approximation (FFA), a time-, charge-, and rigidity-dependent FFA, and a three-dimensional numerical simulation based on the Parker transport equation. Based on AMS-02 latest antiproton data (2025), our results show that the significance of the DM signal is sensitive to the chosen modulation model, with a 2$\sigma$ signal for the FFA (4$\sigma$ if including data from H, He, C, O, B/C, and B/O) and a reduced significance for more complex models. We also address systematic uncertainties using two methods: the add-in-quadrature method, which assumes uncorrelated uncertainties between energy bins, and the nuisance parameter method, which treats systematic uncertainties as nuisance parameters during the fitting process. Fitted to AMS-02 antiproton data, DM annihilation to the $b\bar{b}$ scenario with three different solar modulation models shows that the add-in-quadrature method causes overfitting, whereas the nuisance parameters approach leads to underfitting. Statistically, the signal region of the FFA model using the add-in-quadrature method is the most reliable. This work highlights the need for refined solar modulation models and a better treatment of uncertainties for a conclusive interpretation of the AMS-02 data.