We present a statistical analysis of the first 300 stars observed by the
Gemini Planet Imager Exoplanet Survey (GPIES). This subsample includes six
detected planets and three brown dwarfs; from these detections and our contrast
curves we infer the underlying distributions of substellar companions with
respect to their mass, semi-major axis, and host stellar mass. We uncover a
strong correlation between planet occurrence rate and host star mass, with
stars M > 1.5 M⊙ more likely to host planets with masses between 2-13
MJup and semi-major axes of 3-100 au at 99.92% confidence. We fit a
double power-law model in planet mass (m) and semi-major axis (a) for planet
populations around high-mass stars (M > 1.5M⊙) of the form dmdad2N∝mαaβ, finding α = -2.4 ± 0.8 and
β = -2.0 ± 0.5, and an integrated occurrence rate of 9−4+5%
between 5-13 MJup and 10-100 au. A significantly lower occurrence rate
is obtained for brown dwarfs around all stars, with 0.8−0.5+0.8% of
stars hosting a brown dwarf companion between 13-80 MJup and 10-100
au. Brown dwarfs also appear to be distributed differently in mass and
semi-major axis compared to giant planets; whereas giant planets follow a
bottom-heavy mass distribution and favor smaller semi-major axes, brown dwarfs
exhibit just the opposite behaviors. Comparing to studies of short-period giant
planets from the RV method, our results are consistent with a peak in
occurrence of giant planets between ~1-10 au. We discuss how these trends,
including the preference of giant planets for high-mass host stars, point to
formation of giant planets by core/pebble accretion, and formation of brown
dwarfs by gravitational instability