Limits on the Abundance of Galactic Planets From Five Years of Planet   Observations
  We search for signatures of planets in 43 intensively monitored microlensing events that were observed between 1995 and 1999. Planets would be expected to cause a short duration (~1 day) deviation on the smooth, symmetric light curve produced by a single-lens. We find no such anomalies and infer that less than 1/3 of the ~0.3 M_sun stars that typically comprise the lens population have Jupiter-mass companions with semi-major axes in the range of 1.5 AU <a < 4 AU. Since orbital periods of planets at these radii are 3-15 years, the outer portion of this region is currently difficult to probe with any other technique. 
M.D. Albrow, J. An, J.-P. Beaulieu, J.A.R. Caldwell, D.L. DePoy, M.   Dominik, B.S. Gaudi, A. Gould, J. Greenhill, K. Hill, ...