A search for temporal variation of the fine-structure constant in atomic dysprosium

Frequencies of radio-frequency (rf) electric-dipole (E1) transitions in atomic dysprosium have been measured over a 74-day period. These transitions occur between two nearly degenerate opposite parity levels, which have high sensitivity to changes in the fine structure constant, alpha. From these measurements, a limit on the temporal variation of a&d2;/a has been placed at | a&d2;/a | < 5.6 x 10-15/yr (1sigma C.L.).; The experimental technique first entails three optical transitions to populate an atomic beam of dysprosium to the odd parity level. An rf electric field then excites atoms to the even parity level, which decays via a two-step process. To sensitively determine the rf transition frequency, modulation of the rf electric; field frequency with synchronous detection of the 1st- and 2nd-harmonic components of the second-step fluorescence signal is employed.; Because dysprosium has many stable isotopes, some with hyperfine levels, many different rf transitions can be utilized. This is an important consideration with regard to sensitivity to systematic effects. For this search, three rf transitions were chosen based on the size of the rf transition frequency and/or signal: the 3.1-MHz transition (F = 10.5 → F = 10.5) in 163Dy, the 235-MHz transition in 162Dy, and the 754-MHz transition in 164Dy.; Systematic effects have been investigated and analyzed. Collisional shifts due to residual background gases have been observed and corresponding shift rates have been accurately measured. Relatively large shifts due to changes in the rf electric-field amplitude, temperature of the atomic beam source, and frequency detuning of the population lasers; have been observed for the 754-MHz transition. These shifts are believed to be caused by the geometry of the electric-field electrodes, which was originally used in and optimized for a previous search for parity violation involving low-frequency electric fields. Excluding data from this transition, a limit on a&d2;/a comparable to the best limits has been attained, with the possibility of further significant improvement.