The E2 6S-7S amplitude in Cesium and its importance in a precise calibration of Epv1

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Abstract
Among all 6S-7S Cs transition amplitudes, Mhf1 induced by the off-diagonal hyperfine interaction has recently become the most precisely known on theoretical grounds. Consequently, it is now possible to achieve 0.3 % accuracy in the calibration of the parity violating amplitude E pv1 using Mhf1 as a standard. For this reason we address here the problem of a precise interpretation of the signals involved in the calibration procedure, namely those providing the ratio of Mhf1to the normal M1 amplitude. We show that the interpretation of the data can no longer omit the quadrupole electric amplitude E2 induced by the off diagonal hyperfine interaction. Including E2 substantially improves the agreement between determinations of Mhf 1/M1 derived from experiments based on different principles. A reanalysis of current experimental data gives Mhf 1/M1 = (188.6 ± 1.7) x 10-3 and E 2/Mhf1 = (42 ± 13) x 10-3. The last result is compatible with a recent theoretical evaluation. Using the revised Mhf1/β empirical ratio and the theoretical value of Mhf1 we arrive at a determination of the Stark vector polarizability β = (27.17 ± 0.35) a3 0 in excellent agreement with the semi-empirical determination βse = (27.2 ± 0.4) a 30