Particle energy probability density functions obtained from “2.5D” particle-in-cell (PIC) simulations of decaying magnetically dominated turbulence for varying magnetization parameters and strengths of the guide field. Details of the simulations can be found in C. Vega et al. (2022b). The turbulence was initialized in a square box L × L = 2010d_e × 2010d_e, using N = 8 first Fourier modes. The outer scale of the turbulence is then defined as L_out = L/8. In the top panel, we calculate the maximum gamma factor as ﹩{\gamma }_{{\rm{\max }}}={L}_{out}\sqrt{{\sigma }_{0}}/{d}_{e}﹩, with B₀/δB₀ = 1. In the bottom panel, the role of the guide field is played by large-scale turbulent fluctuations, allowing us to effectively assume B₀/δB₀ ≈ 1 and use the definition ﹩{\gamma }_{{\rm{\max }}}={L}_{out}\sqrt{{\tilde{\sigma }}_{0}}/{d}_{e}﹩.