Experimental determination of the helium 2(3)P(1)-1(1)S0 transition rate

We present the first experimental determination of the 2(3)P(1)-1(1)S0 transition rate in helium and compare this measurement with theoretical quantum-electrodynamic predictions. The experiment exploits the very long (approximately 1 minute) confinement times obtained for atoms magneto-optically trapped in an apparatus used to create a Bose-Einstein condensate of metastable (2(3)S1) helium. The 2(3)P(1)-1(1)S0 transition rate is measured directly from the decay rate of the cold atomic cloud following 1083 nm laser excitation from the 2(3)S1 to the 2(3)P1 state, and from accurate knowledge of the 2(3)P1 population. The value obtained is 177+/-8 s(-1), which agrees very well with theoretical predictions, and has an accuracy that compares favorably with measurements for the same transition in heliumlike ions higher in the isoelectronic sequence.