We thoroughly study the photo-disintegration of ${}^4\mathrm{He}$ on the cosmic microwave background using the most recent cross-section data from both the inclusive measurement observing the analog of the giant dipole resonance in ${}^4\mathrm{He}$ through the charge-exchange spin-flip ${}^4\mathrm{He}$ (${}^7\mathrm{Li},{}^7\mathrm{Be}$) reaction and from measurements of exclusive two-body and three-body processes: ${}^4\mathrm{He}(\gamma ,p){}^3\mathrm{H}$, ${}^4\mathrm{He}(\gamma ,n){}^3\mathrm{He}$, and ${}^4\mathrm{He}(\gamma ,pn){}^2\mathrm{H}$. We show that the present-day (redshift $z=0$) mean-free path of ultrarelativistic (Lorentz factor $\sim {10}^{10}$) helium nuclei increases by more that 15% with respect to previous estimates adopted as benchmarks for Monte Carlo simulation codes of ultrahigh-energy cosmic ray propagation. This implies that the physical survival probability of ${}^4\mathrm{He}$ nuclei would be larger than predicted by existing event generators. For example, for $E\sim 10^{10.8}\mathrm{GeV}$ and a propagation distance of 3.5 Mpc, the ${}^4\mathrm{He}$ intensity would be 35% larger than the output of the CRPropa 3 program and 42% larger than the output of the SimProp v2r4 program. We provide new parametrizations for the two-body and three-body photo-disintegration cross sections of ${}^4\mathrm{He}$, ${}^3\mathrm{He}$, tritium, and deuterium.

• Received 10 May 2018

DOI:https://doi.org/10.1103/PhysRevD.98.043001