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, \(L_3∝{\lambda ^}^4\) , 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.