Four-Dimensional Ghost Unmasked in CERN's SPS
Physicists at CERN traced a time-evolving resonance inside the Super Proton Synchrotron (SPS) that quietly degrades particle beams. Using a four-dimensional Poincaré surface-of-section, they map fixed harmonic lines that predict where particles cluster, revealing the hidden ‘ghost’ and offering strategies to dampen its effects and guide the design of future accelerators.