High-accuracy measurement of the 87 Rb ground-state hyperfine splitting in an atomic fountain

We describe the operation of a laser-cooled rubidium 87 Rb frequency standard.We present a new measurement of the 87 Rb hyperfine frequency with a 1.3 10 -14 relative accuracy, by comparison with a Cs fountain primary standard.The measured 87 Rb ground-state hyperfine splitting is 87 Rb = 6 834 682 610.90429(9)Hz.This value differs from previously published values (see Essen L.,