Hadrophobic axion-like particles (ALPs) coupling primarily to photons and electrons are well-motivated new physics targets, yet previous beam dump sensitivity projections rarely include their production from electromagnetic cascades in the target. We show that shower particles dominate ALP production across the full relevant mass range, yielding order-of-magnitude enhancements in both electron and proton beam dump experiments. We present updated projections for SHiP (CERN) and BDX (J-Lab) that extend their reach into unexplored ALPs parameter space. Using full cascade simulations including transverse dynamics and angular distributions, we demonstrate that electromagnetic showers are not a correction but an essential component of accurate sensitivity projections, with implications for both upcoming experiments and reanalysis of historic data.
Samuel Patrone, PhD Student, Caltech
Host: Adrian Thompson