. at om - p h ] 1 7 O ct 2 00 3 Black Body Radiation Shift of the 133 Cs Hyperfine Transition Frequency

We report the theoretical evaluations of the static scalar polarizability of the 133Cs ground state and of the black body radiation shift induced on the transition frequency between the two hyperfine levels with mF = 0. This shift is of fundamental importance in the evaluation of the accuracy of the primary frequency standards based on atomic fountains and employed in the realization of the SI second in the International Atomic Time (TAI) scale at the level of 1× 10−15. Our computed value for the polarizability is α0 = (6.600±0.016)×10−39 Cm2/V in agreement at the level of 1×10−3 with recent theoretical and experimental values. As regards the black body radiation shift we find for the relative hyperfine transition frequency β = (−1.49± 0.07)× 10−14 at T = 300 K in agreement with frequency measurements reported by our group and by Bauch and Schröder [Phys. Rev. Lett. 78, 622, (1997)]. This value is lower by 2 × 10−15 than that obtained with measurements based on the dc Stark shift and with the value commonly accepted up to now. PACS number(s): 32.60.+i, 32.10.Dk, 06.30.Ft