BOSE-EINSTEIN CONDENSATION IN A DILUTE GAS - MEASUREMENT OF ENERGY AND GROUND-STATE OCCUPATION

We measure the ground-state occupation and energy of a dilute Bose gas of Rb-87 atoms as a function of temperature. The ground-state fractio n shows good agreement with the predictions for an ideal Bose gas in a 3D harmonic potential. The measured transition temperature is 0.94(5) T-o, where T-o is the value for a noninteracting gas in the thermodyna mic limit. We determine the energy from a model-independent analysis o f the velocity distribution, after ballistic expansion, of the atom cl oud. We observe a distinct change in slope of the energy-temperature c urve near the transition, which indicates a sharp feature in the speci fic heat.