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We report the results of the statistical analysis of planetary signalsdiscovered in MOA-II microlensing survey alert system events from 2007 to 2012.We determine the survey sensitivity as a function of planet-star mass ratio,$q$, and projected planet-star separation, $s$, in Einstein radius units. Wefind that the mass ratio function is not a single power-law, but has a changein slope at $q \sim 10^{-4}$, corresponding to $\sim 20 M_{\oplus}$ for themedian host star mass of $\sim 0.6 M_{\odot}$. We find significant planetarysignals in 23 of the 1474 alert events that are well characterized by theMOA-II survey data alone. Data from other groups are used only to characterizeplanetary signals that have been identified in the MOA data alone. Thedistribution of mass ratios and separations of the planets found in our sampleare well fit by a broken power-law model of the form $dN_{\rm pl}/(d{\rm log}q\ d{\rm log} s) = A (q/q_{\rm br})^n s^m \, {\rm dex}^{-2}$ for $q > q_{\rmbr}$ and $dN_{\rm pl}/(d{\rm log} q\ d{\rm log} s) = A (q/q_{\rm br})^p s^m \,{\rm dex}^{-2}$ for $q < q_{\rm br}$, where $q_{\rm br}$ is the mass ratio ofthe break. We also combine this analysis with the previous analyses of Gould etal. and Cassan et al., bringing the total sample to 30 planets. This combinedanalysis yields $A = 0.61^{+0.21}_{-0.16}$, $n =-0.93\pm 0.13$, $m =0.49_{-0.49}^{+0.47}$ and $p = 0.6^{+0.5}_{-0.4}$ for $q_{\rm br}\equiv1.7\times 10^{-4}$. The unbroken power law model is disfavored with a $p$-valueof 0.0022, which corresponds to a Bayes factor of 27 favoring the brokenpower-law model. These results imply that cold Neptunes are likely to be themost common type of planets beyond the snow line.

The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass