Richard J. Fletcher, Alexander L. Gaunt, Nir Navon, Robert P. Smith, Zoran Hadzibabic
We study the stability of a thermal $^{39}$K 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, $L_3 \propto \lambda^4$, is three times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes $^{39}$K particularly promising for studies of many-body physics in a unitary Bose gas.
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http://arxiv.org/abs/1307.3193
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