  We report a thorough investigation of finite-temperature effects on
three-body recombination near a triatomic Efimov resonance in an ultracold gas
of cesium atoms. Our measurements cover a wide range from a near-ideal
realization of the zero-temperature limit to a strongly temperature-dominated
regime. The experimental results are analyzed within a recently introduced
theoretical model based on a universal zero-range theory. The
temperature-induced shift of the resonance reveals a contribution that points
to an energy-dependence of the three-body parameter. We interpret this
contribution in terms of the finite range of the van der Waals interaction in
real atomic systems and we quantify it in an empirical way based on length
scale arguments. A universal character of the corresponding resonance shift is
suggested by observations related to other Efimov resonances and the comparison
with a theoretical finite-temperature approach that explicitly takes the van
der Waals interaction into account. Our findings are of importance for the
precise determination of Efimov resonance positions from experiments at finite
temperatures.
