  We report first results from the Anglo-Australian Telescope Rocky Planet
Search - an intensive, high-precision Doppler planet search targeting low-mass
exoplanets in contiguous 48 night observing blocks. On this run we targeted 24
bright, nearby and intrinsically stable Sun-like stars selected from the
Anglo-Australian Planet Search's main sample. These observations have already
detected one low-mass planet reported elsewhere (HD16417b), and here we
reconfirm the detection of HD4308b. Further, we have Monte-Carlo simulated the
data from this run on a star-by-star basis to produce robust detection
constraints. These simulations demonstrate clear differences in the exoplanet
detectability functions from star to star due to differences in sampling, data
quality and intrinsic stellar stability. They reinforce the importance of
star-by-star simulation when interpreting the data from Doppler planet
searches. The simulations indicate that for some of our target stars we are
sensitive to close-orbiting planets as small as a few Earth masses. The two
low-mass planets present in our 24 star sample indicate that the exoplanet
minimum mass function at low masses is likely to be a flat alpha ~ -1 (for
dN/dM proportional to M^alpha) and that between 15+/-10% (at alpha=-0.3) and
48+/-34% (at alpha=-1.3) of stars host planets with orbital periods of less
than 16 days and minimum masses greater than 3 Mearth.
