Stability of a Unitary Bose Gas

We study the stability of a thermal K-39 Bose gas across a broad Feshbach resonance, focusing on the unitary regime, where the scattering length a exceeds the thermal wavelength lambda. We measure the general scaling laws relating the particle-loss and heating rates to the temperature, scattering length, and atom number. Both at unitarity and for positive a << lambda we find agreement with three-body theory. However, for a < 0 and away from unitarity, we observe significant four-body decay. At unitarity, the three-body loss coefficient, L-3 proportional to lambda(4), is 3 times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes K-39 particularly promising for studies of many-body physics in a unitary Bose gas.