Search for parity nonconserving optical rotation in atomic samarium

We have searched for parity nonconserving (PNC) optical rotation in five optical transitions within the 4f⁶6s² ground configuration of atomic samarium using laser polarimetry. It had been suggested that these transitions might be favorable for studying electroweak effects because the upper levels have close-lying levels of opposite parity which might give rise to strong mixing by the PNC Hamiltonian H_PNC. In terms of the usual parameter R[=Im(E_PNC/M)], we obtain (in units of 10^-8) R₆₆₂=2.1(1.8), R₆₂₈=-7(16), R₆₁₁=-6(8), R₅₆₉=-17(30), and R₅₅₈=-6(12), where the subscripts give the wavelengths of the transitions. The values of R are not significantly greater than those already reported for the heavy elements bismuth, lead, and thallium, and we conclude that the samarium transitions do not offer the prospect of a critical test of electroweak theory. Upper limits on the matrix elements of H_PNC between the upper levels of the transitions and their close-lying opposite-parity neighbors are derived from the results.