Measurement of the blackbody radiation shift of theCs133hyperfine transition in an atomic fountain

Abstract

We used a $\mathrm{Cs}$ fountain to measure the Stark shift of the ground-state hyperfine transition frequency in cesium $\left(9.2\mathrm{GHz}\right)$ due to the electric field of the blackbody radiation. The relative shift at $300\mathrm{K}$ deduced from our measurements, including the leading and the second-order term in temperature, is $(-1.45\pm 0.09)\times {10}^{-14}$ and agrees with our recent theoretical evaluation $(-1.51\pm 0.07)\times {10}^{-14}$ [Micalizio et al. Phys. Rev. A 69, 053401 (2004)]. These values differ from that currently used $(-1.735\pm 0.003)\times {10}^{-14}$, with significant implications on frequency standards accuracy, on clocks comparison and on a variety of high-precision physics tests, such as the time stability of fundamental constants.