Stability of a Unitary Bose Gas

We study the stability of a thermal $39K$ 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 $a\ll \lambda$ 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, $L_3\propto {\mathrm{\lambda ^}}^4$ , is 3 times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes $39K$ particularly promising for studies of many-body physics in a unitary Bose gas.