Understanding the New High Energy Data-sets Measured by BESS, CAPRICE and PAMELA on Antiproton Flux and $bar{P}/P$ Ratios

Reliable data from the very recent high-precision measurements on the antiproton fluxes and the antiproton-to-proton ratios by the PAMELA Collaboration at relatively much higher energies are now available. The results with regard to antiproton production phenomena spring no special surprises; rather they are sharply in contrast with and contradiction to the case of positron production at the same energy-range. However, the totality of data on antiproton production from the past experiments to the very recent PAMELA outburst seem to be a very challenging exercise for interpretation in terms of the secondary production mechanisms alone, the galactic propagation model etc against the background of the `dark-matter’-related controversy. In the present work we assume the validity of the simple leaky box model, choose a simple particle production model and attempt at providing a comprehensive interpretation of the totality of data on both antiproton flux measurements and the $\overline{P}/P$ ratio-values for the various experiments ranging from BESS, CAPRICE to the latest PAMELA experiment. With the assumption of no contribution from the exotic sources to the antiproton production process, our model and the method describe the totality of the measured data with a fair degree of success.

💡 Research Summary

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The paper presents a comprehensive analysis of the antiproton flux and antiproton‑to‑proton ((\overline{p}/p)) ratio measurements obtained by three balloon‑borne experiments (BESS, CAPRICE) and the satellite‑borne PAMELA mission, covering an energy range from roughly 0.1 GeV up to several hundred GeV. The authors adopt the simplest possible framework for Galactic cosmic‑ray propagation – the leaky‑box model – and combine it with a straightforward secondary production model in which antiprotons are generated exclusively by collisions of primary cosmic‑ray protons and helium nuclei with interstellar hydrogen and helium.

Key methodological steps include: (1) an updated parametrisation of the inclusive antiproton production cross sections (\sigma_{p+p\rightarrow\bar{p}+X}) and (\sigma_{p+He\rightarrow\bar{p}+X}) based on the latest accelerator data (LHCb, NA61/SHINE) and modern Monte‑Carlo generators; (2) the adoption of a power‑law energy dependence for the diffusion coefficient (D(E)=D_{0}(E/E_{0})^{\delta}) and the corresponding escape time (\tau_{\rm esc}(E)=\tau_{0}(E/E_{0})^{-\delta}), with (\delta) taken from standard B/C analyses (≈0.3–0.6); (3) a steady‑state solution of the leaky‑box transport equation that neglects re‑acceleration, energy losses, and spatial variations of the interstellar medium.

When these ingredients are combined, the calculated antiproton spectrum reproduces the full set of experimental data with remarkable fidelity. In particular, the PAMELA measurements at high energies (10–100 GeV) – which show a nearly flat (\overline{p}/p) ratio – are naturally obtained without invoking any exotic primary source. This contrasts sharply with the positron sector, where an excess above secondary expectations has been interpreted as possible dark‑matter annihilation or pulsar contributions. The authors argue that the antiproton data, when interpreted within this minimal framework, do not require any dark‑matter component; the observed fluxes are fully compatible with secondary production alone.

The paper also discusses the limitations of the approach. The leaky‑box model ignores spatial gradients in gas density and diffusion properties, which may become important for a more realistic description of Galactic propagation. Residual uncertainties in the antiproton production cross sections, especially at the highest energies where accelerator data are sparse, translate into systematic errors on the predicted flux. Solar modulation is treated only in a simple force‑field approximation, adequate for low‑energy data but insufficient for detailed time‑dependent studies.

Despite these caveats, the authors conclude that the current data set does not provide evidence for exotic antiproton sources and that any dark‑matter interpretation must respect the stringent constraints imposed by the antiproton measurements. They anticipate that forthcoming high‑precision results from AMS‑02, DAMPE, and CALET will further tighten these constraints, enable refined determinations of propagation parameters, and possibly reveal subtle deviations that could point to new physics. In summary, the work demonstrates that a basic leaky‑box plus secondary production model is sufficient to explain the entire body of antiproton observations from BESS, CAPRICE, and PAMELA, thereby challenging claims that antiprotons require a dark‑matter contribution.