Precision cross-sections for advancing cosmic-ray physics and other applications: a comprehensive programme for the next decade

Abstract

Cosmic-ray physics in the GeV-to-TeV energy range has entered a precision era thanks to recent data from space-based experiments. However, the poor knowledge of nuclear reactions, in particular for the production of antimatter and secondary nuclei, limits the information that can be extracted from these data, such as source properties, transport in the Galaxy and indirect searches for particle dark matter. The Cross-Section for Cosmic Rays at CERN workshop series has addressed the challenges encountered in the interpretation of high-precision cosmic-ray data, with the goal of strengthening emergent synergies and taking advantage of the complementarity and know-how in different communities, from theoretical and experimental astroparticle physics to high-energy and nuclear physics. In this paper, we present the outcomes of the third edition of the workshop that took place in 2024. We present the current state of cosmic-ray experiments and their perspectives, and provide a detailed road map to close the most urgent gaps in cross-section data, in order to efficiently progress on many open physics cases, which are motivated in the paper. Finally, with the aim of being as exhaustive as possible, this report touches several other fields -- such as cosmogenic studies, space radiation protection and hadrontherapy -- where overlapping and specific new cross-section measurements, as well as nuclear code improvement and benchmarking efforts, are also needed. We also briefly highlight further synergies between astroparticle and high-energy physics on the question of cross-sections.

Figures (23)

• Figure 1: Compilation of the cr energy spectrum, scaled by $E^2$ to highlight spectral features (notably the Knee at $\sim\!10^{6}$ GeV and the Ankle at $\sim\!10^{9}$ GeV). Coloured markers and lines show measurements of the total (all-particle) spectrum and individual components (e.g., protons, electrons, positrons, antiprotons (=$\mathrm{\overline{p}}$)), while open symbols indicate neutral particles (diffuse $\gamma$ rays from the Galactic plane and from the isotropic $\gamma$-ray background, and diffuse neutrinos). Diagonal lines represent integral flux levels for reference. The charged-cr data are taken from the crdb 2014AA...569A..32M2020Univ....6..102M2023EPJC...83..971M, with additional $\gamma$-ray and $\nu$ data from Fermi-lat (lat) Fermi-LAT:2012edvFermi-LAT:2015otn and IceCube IceCube:2013low, respectively. The energy reached at the lhc (lhc) at cern is also indicated.
• Figure 2: Relative abundance of elements in the ss (dashed blue line) 2003ApJ...591.1220L and in gcrs (solid orange line), arbitrarily normalised to Fe$\;\equiv1$. The even-odd pattern in the abundances is related to the even-odd nuclear stability effect. In the top panel, beside H and He, elements with near-matching abundances (names above the orange line) are mostly of primary origin, while ss/gcr $\ll 1$ (names below the blue line) are of secondary origin. In the lower panel, the pattern of gcr/ss abundances is less clear, owing to more uncertain data. gcr data were extracted and selected from crdb 2014AA...569A..32M2020Univ....6..102M2023EPJC...83..971M, at $R=5$ GV for $Z\leq28$ and mostly at $E_{\rm k/n}\sim 1.5$ GeV/n ($\sim\!3.82$ GV) for the rest, rescaled to ams flux ratio Fe(3.82 GV)/Fe(5 GV). Also, above $Z=30$, only ratio $x/y$ are measured with, for instance, $y$ the flux of Fe, of all elements $Z\geq55$, $Z\geq70$, or some other charge ranges. These ratios were multiplied by Fe (ams) and combinations of (Yb+W+Pt+Pb)$/y$ flux data ratios to recover $x$. Data are ams AMS:PhysRep2021AMS:Fe-PRL2021AMS:S-PRL2023, heao 1990AA...233...96E, tiger 2009ApJ...697.2083R, Supertiger, 2016ApJ...831..148M, Ariel6 1987ApJ...314..739F, olimpiya 2022AdSpR..70.2674A and uhcreldef 2012ApJ...747...40D.
• Figure 3: For H, He and $\mathrm{\overline{p}}$ (top to bottom), timeline of the highest energy decade (colour-coded) and best precision reached (height of the bars) in cr experiments, based on the data compiled in the crdb 2014AA...569A..32M2020Univ....6..102M2023EPJC...83..971M. The width of the bars indicates the integration time of the cr experiments: very thin widths correspond to balloon flights (few days flights at most), and larger widths correspond to satellite or space (or more rarely ground-based) experiments. The best precision is always achieved at low energies, not at the highest (colour-coded) energy reached. The name of experiments for which datasets were collected over several months or years is indicated on top of the relevant period; some experiments like ams have several datasets published with overlapping periods (same start date but longer integration time), but their name is indicated only once to avoid overlapping text. Note that the Voyager data after 2015 are the only datasets outside the solar cavity.
• Figure 4: Same as Fig. \ref{['fig:CRdata_light']} but for leptons (including the positron fraction, bottom row).
• Figure 5: Same as Fig. \ref{['fig:CRdata_light']}, but for individual elements of broad groups (for the sake of compactness) of heavy nuclei with $Z<30$. For each of these groups, the best precision and highest energy among the elements measured is reported: not all elements in these groups have been measured, and not all experiments have the capability to measure all elements of a given group, usually because of too low abundances.