A laboratory search for variation of the fine-structure constant using atomic dysprosium

Electric-dipole transitions between nearly degenerate, opposite parity levels of atomic dysprosium (Dy) were monitored over an eight-month period to search for a variation in the fine-structure constant, α. The frequencies of these transitions are sensitive to variation of α due to large relativistic corrections of opposite sign for the opposite-parity levels. In this unique system, in contrast to atomic-clock comparisons, the difference of the electronic energies of the opposite-parity levels can be monitored directly utilizing a radio-frequency (rf), electric-dipole transition between them. Our measurements for the frequency variation of the 3.1-MHz transition in 163Dy and the 235-MHz transition in 162Dy can be analyzed for both a temporal variation and a gravitational-potential dependence of α since, during the data acquisition period, the Earth is located at different values of the gravitational potential of the Sun. The data provide a rate of fractional temporal variation of α of (-2.7±2.6)×10-15 yr-1 or a value of (-8.7 ±6.6) ×10-6 for kα, the linear-variation coefficient for α in a changing gravitational potential. These results are independent of assumptions regarding variation of other fundamental constants. The latter result can be combined with other experimental constraints to extract the first limits on ke and kq, which characterize the variation of me/mp and mq/mp in a changing gravitational potential, where me, mp, and mq are electron, proton, and quark masses. All results indicate the absence of significant variation at the present level of sensitivity