[Paper Review] Estimating QCD uncertainties on antiproton spectra from dark-matter annihilation

Adil Jueid, Jochem Kip+2 more|arXiv (Cornell University)|Mar 11, 2022

Dark Matter and Cosmic Phenomena4 citations

TL;DR

This paper provides a systematic, model-independent estimation of QCD uncertainties in antiproton spectra from dark matter annihilation, using tuned parton shower and hadronization parameters in Pythia 8 based on LEP and AMS-02 data. It quantifies uncertainties up to 50% in high-energy regions, with hadronization effects dominating at high energies and reaching 20% in low-energy antiproton spectra, offering conservative uncertainty bands for future dark matter searches.

ABSTRACT

In this talk, we discuss the physics modeling of antiproton spectra arising from dark matter (DM) annihilation or decay in a model-independent manner. The modeling of antiproton spectra contains some intrinsic uncertainties related to QCD parton showers and hadronisation of baryons. We briefly assess the sources of these uncertainties and their impact on antiproton energy spectra for a few selected DM scenarios. The results are provided in tabulated form for future analyses.

Motivation & Objective

• To quantify QCD uncertainties in antiproton spectra from dark matter annihilation, focusing on parton shower and hadronization effects.
• To provide a conservative, data-driven estimate of uncertainties using eigentunes from the Professor optimization tool.
• To assess the impact of these uncertainties on antiproton spectra across different dark matter masses and annihilation channels.
• To deliver tabulated uncertainty bands for use in future dark matter indirect detection analyses, particularly for PPPC4DMID, DarkSusy 6, and MicrOmegas 5.
• To improve the reliability of antiproton-based dark matter searches by accounting for theoretical uncertainties previously overlooked.

Proposed method

• Re-tuned the Lund fragmentation function parameters in Pythia 8.244 using the Professor 2.3.3 optimization tool based on Rivet 3.1.3 measurements.
• Performed eigentune variations at one-, two-, and three-sigma levels corresponding to Δχ²/Ndf = 1, 4, and 9, respectively.
• Used constraints from LEP Z-pole measurements of baryon and meson spectra to guide parameter tuning.
• Generated antiproton spectra for dark matter masses of 10 GeV and 100 GeV across annihilation channels: q̄q, gg, and VV (WW+ZZ).
• Defined the x-variable as x = Ekin / Mχ to normalize kinetic energy relative to dark matter mass for spectral comparison.
• Compared uncertainties from parton shower (Pythia 8) and hadronization (string model) separately, with bands showing ±1σ and ±2σ variations.

Experimental results

Research questions

• RQ1 What is the impact of QCD uncertainties—particularly from parton shower and hadronization—on antiproton spectra from dark matter annihilation?
• RQ2 How do these uncertainties vary with dark matter mass and annihilation channel (e.g., q̄q, gg, VV)?
• RQ3 To what extent do eigentune variations based on LEP and AMS-02 data provide a conservative estimate of theoretical uncertainties?
• RQ4 How do the uncertainties in antiproton spectra compare to those in positron spectra across different energy regions?
• RQ5 What is the maximum uncertainty in antiproton spectra, and where is it dominated by hadronization vs. parton shower effects?

Key findings

• Hadronization uncertainties dominate at high energies, reaching up to 50% in the antiproton spectrum for 100 GeV dark matter, especially in the tail region.
• For 100 GeV dark matter, parton shower uncertainties reach up to 15% in the peak region, while hadronization uncertainties are ~20% in the low-energy region.
• At 10 GeV, QCD uncertainties are subleading, with both parton shower and hadronization effects below 10% across most of the spectrum.
• In the peak region of the antiproton spectrum for q̄q annihilation, uncertainties vanish at x ≈ 0.2 due to cancellation across eigentunes.
• The two-sigma eigentunes provide a balanced and conservative coverage of experimental uncertainties without overshoting data errors.
• The study provides public, tabulated uncertainty bands for antiproton spectra, which are integrated into future versions of PPPC4DMID, DarkSusy 6, and MicrOmegas 5.