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We report tests of local position invariance based on measurements of theratio of the ground state hyperfine frequencies of 133Cs and 87Rb inlaser-cooled atomic fountain clocks. Measurements extending over 14 years set astringent limit to a possible variation with time of this ratio: dln(nu_Rb/nu_Cs)/dt=(-1.39 +/- 0.91)x 10-16 yr-1. This improves by a factor of7.7 over our previous report (H. Marion et al., Phys. Rev. Lett. 90, 150801(2003)). Our measurements also set the first limit to a fractional variation ofthe Rb/Cs ratio with gravitational potential at the level of c^2 dln(nu_Rb/nu_Cs)/dU=(0.11 +/- 1.04)x 10^-6, providing a new stringentdifferential redshift test. The above limits equivalently apply to thefractional variation of the quantity alpha^{-0.49}x(g_Rb/g_Cs), which involvesthe fine structure constant alpha and the ratio of the nuclear g-factors of thetwo alkalis. The link with variations of the light quark mass is also presentedtogether with a global analysis combining with other available highly accurateclock comparisons.

Improved tests of Local Position Invariance using 87Rb and 133Cs fountains