Kendra vant

Inelastic collision rates of trapped metastable hydrogen

We report the first detailed decay studies of trapped metastable (2S) hydrogen. By two-photon excitation of ultracold H samples, we have produced clouds of at least 5x10(7) magnetically trapped 2S atoms at densities greater than 4x10(10) cm(-3) and temperatures below 100 muK. At these densities and temperatures, two-body inelastic collisions of metastable atoms are evident. Experimental values for the total two-body loss rate constant are K-2=1.8(-0.7)(+1.8)x10(-9) cm(3) s(-1) at 87 muK and K-2=1.0(-0.5)(+0.9)x10(-9) cm(3) s(-1) at 230 muK. These results are in the range of recent theoretical calculations for the total 2S-2S inelastic rate constant. The metastable clouds were excited in a gas of ground-state (1S) hydrogen with peak densities reaching 7x10(13) cm(-3). From the one-body component of the metastable decay, we derive experimental upper limits for K-12, the rate constant for loss due to inelastic 1S-2S collisions.