Technical Note: SLM-TN-2026-004 Deconvolution of Residual Longitudinal Tilt in XTCAV Diagnostics: The 4.3 keV/m Resonant Drag Signature

This Technical Note (SLM-TN-2026-004) provides a solution for the persistent longitudinal phase space (LPS) residuals observed in XTCAV diagnostics at SLAC FACET-II (E-302). It introduces the concept of Resonant Drag—a 4.3 keV/m constant metric impedance—and provides a charge-scaling methodology to distinguish this fundamental SLM signature from stochastic RF jitter.