  We have carried out high contrast imaging of 70 young, nearby B and A stars
to search for brown dwarf and planetary companions as part of the Gemini NICI
Planet-Finding Campaign. Our survey represents the largest, deepest survey for
planets around high-mass stars (~1.5-2.5 M_sun) conducted to date and includes
the planet hosts beta Pic and Fomalhaut. We obtained follow-up astrometry of
all candidate companions within 400 AU projected separation for stars in
uncrowded fields and identified new low-mass companions to HD 1160 and HIP
79797. We have found that the previously known young brown dwarf companion to
HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses
58 (+21, -20) M_Jup and 55 (+20, -19) M_Jup, making this system one of the rare
substellar binaries in orbit around a star. Considering the contrast limits of
our NICI data and the fact that we did not detect any planets, we use
high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M_sun
stars can have giant planets greater than 4 M_Jup between 59 and 460 AU at 95%
confidence, and fewer than 10% of these stars can have a planet more massive
than 10 M_Jup between 38 and 650 AU. Overall, we find that large-separation
giant planets are not common around B and A stars: fewer than 10% of B and A
stars can have an analog to the HR 8799 b (7 M_Jup, 68 AU) planet at 95%
confidence. We also describe a new Bayesian technique for determining the ages
of field B and A stars from photometry and theoretical isochrones. Our method
produces more plausible ages for high-mass stars than previous age-dating
techniques, which tend to underestimate stellar ages and their uncertainties.
