  Measurement of the transverse spin dependence of the di-jet opening angle in
pp collisions at sqrt{s}=200 GeV has been performed by the STAR collaboration.
An analyzing power consistent with zero has been observed over a broad range in
pseudorapidity sum of the two jets with respect to the polarized beam
direction. A non-zero (Sivers) correlation between transverse momentum
direction of partons in the initial state and transverse spin orientation of
the parent proton has been previously observed in semi-inclusive deep inelastic
scattering (SIDIS).
  The present measurements are much smaller than deduced from predictions made
for STAR di-jets based on non-zero quark Sivers functions deduced from SIDIS,
and furthermore indicate that gluon Sivers asymmetries are comparably small.
