  We report a high precision measurement of the transverse single spin
asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured
in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant
0.035$ $\GeVcSq$, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
$A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.
