Antiprotons from spallations of cosmic rays on interstellar matter

TL;DR

This study provides a rigorous evaluation of the Galactic secondary antiproton flux within a two-zone diffusion model constrained by cosmic-ray nuclei data. By combining accurately measured proton and helium spectra with DTUNUC-based cross-sections for $p$-He, He-p, and He-He interactions, the authors quantify propagation and nuclear uncertainties and demonstrate that the predicted antiproton flux lies within current experimental data, notably from BESS. The work finds propagation uncertainties of about 10–25% across the energy range and nuclear-physics uncertainties up to roughly 25%, with solar modulation treated separately. It underscores the opportunity to use precise antiproton measurements to probe exotic sources, while identifying nuclear cross-sections, especially for the $p$-$\mathrm{He}$ channel, as the key area for reducing theoretical uncertainties. Overall, the results strengthen the reliability of the secondary antiproton background and inform future searches for primary antiproton signals.

Abstract

Cosmic ray antiprotons provide an important probe for the study of the galactic Dark Matter, as they could be produced by exotic sources. On the other hand, antiprotons are anyway produced by standard nuclear reactions of cosmic ray nuclei on interstellar matter. This process is responsible for a background flux that must be carefully determined to estimate the detectability of an hypothetical exotic signal. Estimates of this background suffer from potential uncertainties of various origins. The propagation of cosmic antiprotons depends on several physical characteristics of the Galaxy which are poorly known. Antiprotons are created from cosmic protons and helium nuclei whose fluxes were not measured with great accuracy until very recently. Calculations of antiproton fluxes make use of nuclear physics models with their own shortcomings and uncertainties. The goal of this paper is to give a new evaluation of the cosmic antiproton flux along with the associated uncertainties. The propagation parameters were tightly constrained in Maurin et al. 2001 by an analysis of cosmic ray nuclei data in the framework of a two-zone diffusion model and we apply these parameters to the propagation of antiprotons. We use the recently published data on proton and helion fluxes, and we find that this particular source of uncertainty has become negligible. The Monte Carlo program DTUNUC was used to carefully examine nuclear reactions. We find that all the cosmic antiproton fluxes naturally coming out of the calculation are fully compatible with experimental data. Uncertainties in this flux have been strongly reduced. Those related to propagation are less than 25%. All other possible sources of uncertainty have also been studied.

Figures (9)

• Figure 1: The upper (lower) curve displays the measured proton (helium) flux along with an analytical fit (see text). On both curves, data are from ams (Alcaraz et al. 2000a, 2000b, 2000c) (crosses) and bess (Sanuki et al. 2000) (filled circles).
• Figure 2: Here are displayed the antiproton production cross-section in p+C (top) and p+Al (bottom) collisions at 12 GeV laboratory kinetic energy. Filled circles are experimental data sugaya and the lines are from our dtunuc simulations. The error bars have been assumed to be $15\%$. This value is usual for such experiments and was suggested by a $\chi^2$ analysis combining most data available.
• Figure 3: Invariant spectrum of $\bar{p}$ in p+Al collisions at 14.6 GeV laboratory momentum. Filled circles are experimental data (Abbott et al. 1993) and the line is from our dtunuc simulation.
• Figure 4: From top to bottom: antiproton differential production cross-section in He--He, p--He and He--p reactions for antiprotons kinetic energy 1.5 GeV, as obtained with dtunuc simulations.
• Figure 5: Solid line shows the total top-of-atmosphere ( toa) secondary antiproton spectrum for the reference set of diffusion parameters (see text for details). Dashed lines are the contributions to this total flux from various nuclear reactions (from top to bottom: p--p, p--He, He--p and He--He). Data points are taken from bess 95+97 (filled circles) and from bess 98 (empty squares).