In 1950, six years before Lee and Yang's famous assertion of a fundamental difference between a left- and right- handed world, Purcell and Ramsey first suggested that discrete symmetries may not be sacred. Specifically Purcell and Ramsey proposed that neutrons and electrons may possess an electric dipole moment (EDM) proportional to spin that violates time-reversal symmetry. Whereas Madam Wu's observation of parity violation in the Beta decay of Cobalt-60 almost immediately verified Lee and Yang?s assertion, Purcell and Ramsey's suggestion of an electric dipole moment launched an experimental hunt that is still ongoing today. This project seeks to continue our progress toward a significant measurement of the e-EDM using PbF. A non-zero e-EDM would break the normal degeneracy between paramagnetic states of molecules that differ only by the direction of rotation with respect to an applied electric field. The strong internal electric field of these molecules causes even a small e-EDM to break this degeneracy by a relatively large amount. Our experimental concept is guided by 6 years of intensive spectroscopy which has led to a detailed understanding of the electronic, vibrational, rotational, hyperfine, Zeeman, and Stark structures of the PbF molecule, with the ground state energy level structure of the X1 state now understood to an accuracy of 200 Hz and the energy level structure of the long-lived A state understood to an accuracy of 10 MHz. The large body of data we have collected on this molecule has led us to an optical double resonance experiment that searches for an e-EDM in the even parity ground state. This molecular state is unique in that it is sensitive to an e-EDM, it has a small magnetic g factor at the electric fields of the experiment, and has a spectroscopy that demonstrates focused (hyperfine resolved) spectra at high electric fields. We will concentrate on necessary details in PbF spectroscopy and the geometric phase effect using a slightly modified molecular beam apparatus with the full optical double resonance technique. This measurement will test models of the geometric phase, which is an important source of systematic error, and our entire data collection system.
The e-EDM search has a history of making dramatic broader impacts. E.g. Ramsey developed the separated oscillator atomic clock that allows timing so accurate that a satellite-based global positioning system is feasible; Eric Cornell has developed a frequency-locked comb-based measurement system with both extremely high resolution and high scan range that may lead to a new era of molecular fingerprinting. Finally, we have developed a high-precision (< 5 MHz) resonant ionization scheme that has an unprecedented combination of resolution and sensitivity. This new technique, pc-REMPI, will be of general spectroscopic use: e.g. trace detection including remote detection of explosives, molecular fingerprinting, chemical reaction dynamics. This grant provides training for graduate students to acquire critical skills that are important for the future scientific work force.
