  We predict ground state cooling of a micro-mechanical oscillator, i.e. a
vibrating end-mirror of an optical cavity, by resonant coupling of mirror
vibrations to a narrow internal optical transition of an ensemble of two level
systems. The particles represented by a collective mesoscopic spin model
implement, together with the cavity, an efficient, frequency tailorable zero
temperature loss channel which can be turned to a gain channel of pump. As
opposed to the case of resolved-sideband cavity cooling requiring a small
cavity linewidth, one can work here with low finesses and very small cavity
volumes to enhance the light mirror and light atom coupling. The tailored loss
and gain channels provide for efficient removal of vibrational quanta and
suppress reheating. In a simple physical picture of sideband cooling, the atoms
shape the cavity profile to enhance/inhibit scattering into higher/lower energy
sidebands. The method should be applicable to other cavity based cooling
schemes for atomic and molecular gases as for molecular ensembles coupled to
stripline cavities.
