Fragmentation Cross Sections for the Understanding of Cosmic-Ray Transport in the Galaxy: Results and Prospects from NA61/SHINE

TL;DR

The paper addresses how accurate fragmentation cross sections shape our understanding of Galactic cosmic-ray transport by reducing uncertainties in secondary production. It presents high-energy fragmentation measurements from NA61/SHINE, including boron production in 12C+p at 13.5 GeV/c per nucleon (2018 pilot) and a high-statistics 2024 run with He–Si projectiles at 12.5 GeV/c per nucleon, plus a 2025 16O run at 150 GeV/c per nucleon to map energy dependence. Key results include measurements of mass-changing and charge-changing cross sections that align with prior high-energy data and model parametrizations, as well as boron-isotope production cross sections (11C, 11B, 10B) that constrain high-energy boron yields. These findings tighten the fragmentation network used in cosmic-ray propagation models and enable direct tests of energy dependence up to SPS energies, with plans to extend measurements to heavier elements in the future.

Abstract

Accurate measurements of cosmic-ray fragmentation cross sections are essential for maximizing the physics potential of precise measurements of secondary and primary cosmic-ray fluxes from current balloon and space-borne experiments. NA61/SHINE, operating at the CERN SPS H2 beamline, is uniquely suited to studying these interactions at energies above 10 GeV/c per nucleon. In this contribution, we present the fragmentation cross sections for the breakup of carbon into $^{10}$B, $^{11}$B and $^{11}$C at 13.5 GeV/c per nucleon that are needed for interpreting the cosmic-ray boron-to-carbon ratio. These results are based on data from a pilot run conducted in 2018. We also give an overview of the high-statistics data-taking campaign in 2024, which covered projectile nuclei from lithium to silicon. With over 40 million recorded beam triggers, this data set will enable the reconstruction of the full reaction network required to study light secondary cosmic rays. Furthermore, we report on data collected in 2025 with a primary oxygen beam at 150 GeV/c per nucleon, aimed at verifying the expected flattening of fragmentation cross sections at high energies.

Figures (6)

• Figure 1: Schematic layout of the NA61/ SHINE setup at the CERN SPS, used to measure nuclear fragmentation at 13.5 $A\,\text{GeV}/c$ during the 2018 pilot run and at 12.5 $A\,\text{GeV}/c$ during the 2024 data taking.
• Figure 2: Particle identification upstream (left) and downstream (right) of the target (middle panel).
• Figure 3: The charge-changing (${\Delta{Z}\geq1}$) and mass-changing (${\Delta{A}\geq1}$) cross section of $^{12}\mathrm{C}$ on CH$_2$ (left) and C (right) targets as function of kinetic energy per nucleon. Our results NA61SHINE:2024rzv are shown as solid circles and squares. Previous measurements of the charge-changing cross sections are shown as open circles and previous measurements of the mass-changing or inelastic cross section are displayed as open squares Ferrando1988GolovchenkoWebber:1990_PRCSCHALL1996221CHULKOV2000330Jaros:1978Akisenko:1980Zhang:2002Zheng:2002Fang:2000Yan:2020Kanungo:2016. The charge-changing cross section derived from AMS cosmic-ray data Yan:2020 is highlighted with an arrow. The curves are taken from Ref. SIHVER2012812, showing the parametrizations of Refs. TRIPATHI1996347Takechi2009Sihver2009, while the FLUKA 2024.1 predictions Ballarini:2024isa were taken from Ref. flukapriv.
• Figure 4: Isotope production cross sections of $^{11}\mathrm{C}$, $^{11}\mathrm{B}$ and $^{10}\mathrm{B}$ fragments in $^{12}\mathrm{C}$+p interactions measured with NA61/ SHINE NA61SHINE:2024rzv (solid symbols), previous measurements Fontes:1977qqKorejwo:1999Korejwo:2002Olson:1983Webber:1990aipc (open symbols) and a fit to previous data from Ref. Evoli:2019pr (lines).
• Figure 5: Beam composition during data taking in December 2024 at 12.5 $A\,\text{GeV}/c$. The time-of-flight difference relative to fragments with $A/Z=2$ is shown on the $y$-axis, and the charge number $Z$, measured with a scintillator located just upstream of the NA61 target, on the $x$-axis. Isotopes relevant for cosmic-ray transport Genolini:2023kcj are labeled and highlighted by red contours. The data shown here are based on a very preliminary calibration and represent only a few percent of the full data set.