We report the discovery of a microlensing planet OGLE-2012-BLG-0950Lb with the planet/host mass ratio of q \simeq 2 \times 10 ^ { -4 } .
A long term distortion detected in both MOA and OGLE light curve can be explained by the microlens parallax due to the Earth ’ s orbital motion around the Sun .
Although the finite source effect is not detected , we obtain the lens flux by the high resolution Keck AO observation .
Combining the microlens parallax and the lens flux reveal the nature of the lens : a planet with mass of M _ { p } = 35 ^ { +17 } _ { -9 } M _ { \oplus } is orbiting around a M-dwarf with mass of M _ { host } = 0.56 ^ { +0.12 } _ { -0.16 } M _ { \odot } with a planet-host projected separation of r _ { \perp } = 2.7 ^ { +0.6 } _ { -0.7 } AU located at D _ { L } = 3.0 ^ { +0.8 } _ { -1.1 } kpc from us .
This is the first mass measurement from only microlens parallax and the lens flux without the finite source effect .
In the coming space observation-era with Spitzer , K2 , Euclid , and WFIRST , we expect many such events for which we will not be able to measure any finite source effect .
This work demonstrates an ability of mass measurements in such events .