We measured the integrated Stokes parameters P1, P2, and P3 of Zn (43PJ – 53S1) florescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)53S1 state. This work was motivated by a similar study from several years ago by Pravica et al. (2011), in which they measured non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)53S1 excitation and the first cascading (4s5p)53PJ threshold.
The experiment of Pravica et al. has raised serious questions regarding fundamental theoretical assumptions about the nature of spin-dependent interactions in electron-atom scattering physics. Their main result is so unexpected that it can rightfully be regarded as the atomic collisions physics equivalent of the observation of super-luminal neutrinos at CERN several years ago.
In our experiment, the fluorescence is observed in the direction of the initial electron spin polarization. The atomic Zn target was produced by a Zn oven that directed an atomic beam at right angles to both the fluorescence observation direction and the electron beam axis. Using a standard GaAs polarized electron source we observe optical excitation functions in agreement with those of previous experimental and theoretical results. In the cascade-free range of excitation between 6.65 eV and 7.6 eV, we measured P2 and find its values in this range to be consistent with theory and inconsistent with the non-zero measurements of Pravica et al.