Search for variations of fundamental constants using atomic fountain clocks -: art. no. 150801

Over five years, we have compared the hyperfine frequencies of Cs-133 and Rb-87 atoms in their electronic ground state using several laser-cooled Cs-133 and Rb-87 atomic fountains with an accuracy of similar to10(-15). These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies: d/dt ln[(nu(Rb))/(nu(Cs))] = (0.2 +/- 7.0) x 10(-16) yr(-1) (1sigma uncertainty). The same limit applies to a possible variation of the quantity (mu(Rb)/mu(Cs))alpha(-0.44), which involves the ratio of nuclear magnetic moments and the fine structure constant.