Polarized Structure Function $\sigma_{LT'}$ for $p({\vec e},e'K^+)\Lambda$ in the Nucleon Resonance Region

The first measurements of the polarized structure function $\sigma_{LT'}$ for the reaction $p(\vec e,e'K^+)\Lambda$ in the nucleon resonance region are reported. Measurements are included from threshold up to $W$=2.05 GeV for central values of $Q^2$ of 0.65 and 1.00 GeV$^2$, and nearly the entire kaon center-of-mass angular range. $\sigma_{LT'}$ is the imaginary part of the longitudinal-transverse response and is expected to be sensitive to interferences between competing intermediate s-channel resonances, as well as resonant and non-resonant processes. The results for $\sigma_{LT'}$ are comparable in magnitude to previously reported results from CLAS for $\sigma_{LT}$, the real part of the same response. An intriguing sign change in $\sigma_{LT'}$ is observed in the high $Q^2$ data at $W\approx 1.9$ GeV. Comparisons to several existing model predictions are shown.