Precision Measurement of Parity Non-Conserving, Weak-force Induced Transitions in Atomic Cesium

Purdue University, West Lafayette IN

Investigators

Abstract

We understand the universe in which we live through four fundamental forces: gravitational, electromagnetic, weak (responsible for radioactivity and beta decay), and strong (which provides the force that binds atomic nuclei together). A theoretical framework that unifies three of these forces (electromagnetic, weak and strong) is known as the standard model, and has been very successful at explaining a broad range of observables and predicting others. There are, however, several notable effects that the standard model has not been able to explain, including the preponderance of regular matter in the universe (but very little anti-matter), and the existence and nature of dark matter and dark energy. The evidence of the existence of dark matter is provided by observations of the rotation of galaxies. From this, we know that the universe contains much more matter than we have been able to observe. But we know very little about what this "dark" matter is, or how, other than through gravity, it interacts with the matter that we can observe. In this project, the principal investigator and his team will use precision measurements of extremely weak optical interactions of a laser field with cesium atoms to test the standard model, and to search for signatures of physical effects that lie outside the realm of the standard model. The Principal Investigator and his research team are developing two measurement techniques to probe the weak force interactions in atomic cesium. Each measurement technique is a variant of two-color coherent control, in which the amplitudes for two transitions in the optical or radio-frequency range interfere with one another. One measurement, based on the 6s 2S1/2 → 7s 2S1/2 transition, is designed to provide an improved value of the weak charge of the cesium nucleus. The second, based on the 9.19 GHz transition between the hyperfine components of the ground state, is due solely to nuclear-spin dependent contributions such as the anapole moment of the nucleus. Atomic cesium was, of course, the choice of Wieman for his 1997 work, and that group's measurement is still the most precise measurement of the weak charge in any atomic species. Cesium is also the only species in which the nuclear anapole moment has been observed. The degree to which the measurement of the weak charge agrees with the standard model prediction will place constraints upon various models of physics beyond the standard model. The coherent control technique is expected to result in a reduction of the susceptibility of the measurement to systematic errors, critical for the success of these measurements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.