This project is a continuation of an ongoing experiment to measure the strength of certain types of electroweak interactions. The electroweak force (one of the four fundamental forces in nature) gives rise to an intrinsic energy difference between right- and left-handed configurations of particles and electromagnetic fields. Here, molecules are used in a novel scheme to amplify this (usually tiny) effect by many orders of magnitude. This should make it possible to measure as-yet unseen features of the electroweak force, in particular how it is modified by the presence of the strong force inside an atomic nucleus. Our table-top scale experiment is designed to provide data complementary to work ongoing at large accelerator laboratories.

This project involves extensive student training. One current PhD student is completing his thesis on the experiment, and another will be sought, and undergraduates are frequently involved in the work. This project will also continue to include significant collaborative effort such as: participation of a faculty member from the US Coast Guard Academy; cross-disciplinary collaborations with chemists; and work with theorists in both Russia and the U.S. In addition, the wide range of technical challenges we face and solve naturally leads to spin-offs with possible broad applications, such as new sensitive methods for detecting trace amounts of certain molecules; new methods for precisely measuring magnetic fields; etc.

Project Report

The long-term goal of this project was to study certain aspects of the weak interaction—one of the four fundamental forces of nature (along with gravity, electromagnetism, and the strong force that binds together protons and neutrons in the atomic nucleus). True to its name, the weak interaction produces extremely tiny changes in the energy of quantum-mechanical states in atoms and molecules. Our experiment uses a novel approach that employs some features of diatomic molecules to amplify the effect of the weak interaction by a factor of roughly 100 billion, compared to the case of atoms where previous studies have been made. This amplification should allow us to measure certain aspects of the weak interaction that have previously been impossible to determine. For example, the magnitude of the weak interaction between neutrons and protons is modified by the presence of strong forces, so that the weak force between an isolated proton-neutron pair is different from that between a proton and neutron inside a large atomic nucleus. Measurements of these aspects of the weak interaction will allow a comparison to theoretical predictions, cross-checking the validity of one of the most fundamental theories in science in ways not before possible. To measure the weak interaction, we beam molecules into a region surrounded by electrodes and current-carrying wires, which can create configurations of electric and magnetic fields that are mirror images of each other. The weak interaction shows up as a minute change in the molecular energy when we switch from one configuration to its mirror image. We then measure the energy shifts using a series of precisely tuned lasers. Our experiment requires extremely precise knowledge of, and control over, electric and magnetic fields in the region where we measure the molecular energy. Over the course of this grant, we have developed systems to both measure and manipulate these fields with the required accuracy. We constructed a complex set of electrodes and a computer-controlled system for applying voltages to them, so that our electric field could be precisely controlled in magnitude and shape. We also developed a novel method for using the molecules to directly measure the shape and magnitude of both the electric field and the magnetic field, with extraordinary sensitivity. For example, we can routinely see variations in our magnetic field at the level of 5 parts per billion. With the necessary level of control over electric and magnetic fields, we made measurements to demonstrate that we have a complete understanding of the quantum-mechanical states of the molecules in our experiment. We precisely measured how the molecular energies are affected by these fields, validating previous theoretical calculations of this. We also determined that a particular type of electric-field induced energy shift, which had previously been ignored in related experiments, was in fact important to account for. Overall, we showed that our understanding of the molecular states used in our experiment is thorough and precise. Finally, using this system we made initial, preliminary measurements of the effects of the weak interaction in our system. While these measurements must be improved in a variety of ways before they can be considered conclusive, we were able to demonstrate sensitivity to the weak interaction exceeding that of any previous experiment. This gives us great optimism that we will be able to complete the sought-for measurements of the weak interaction in the near future. In the meantime, our ability to understand and control the relevant quantum states of molecules may prove to have impacts well outside the original goals of our study. We have already demonstrated that our system can be used to make extremely precise measurements of electric and magnetic fields. Our system also has been proposed for use as a novel sensor for microwave radiation. It has also been proposed for use as a way to simulate the behavior of a very general but poorly understood class of chemical reactions. Hence, as often happens in the course of experiments aimed at studying fundamental phenomena, our work could end up having impact in more applied realms. In addition to the Intellectual Merit of the work described above, our work has had substantial Broader Impacts. Most significantly, this grant contributed to the education and training of two postdoctoral scholars, three doctoral students, three undergraduates, and one high school student. These young scientists have had to develop extensive skills and experience in a wide variety of technical and scientific areas, including analog, digital, and radiofrequency electronics design, construction, and testing; design and use of lasers, optics, and electro-optics; theory and practice of magnetic resonance techniques; software development and use for data acquisition and experimental modeling; computer-automated design for mechanical, optical, and vacuum equipment; etc. Our project also included the participation of one faculty member at a nearby undergraduate-only institution, where on-campus research is not feasible.

Agency
National Science Foundation (NSF)
Institute
Division of Physics (PHY)
Application #
1068575
Program Officer
John D. Gillaspy
Project Start
Project End
Budget Start
2011-09-01
Budget End
2014-08-31
Support Year
Fiscal Year
2010
Total Cost
$450,000
Indirect Cost
Name
Yale University
Department
Type
DUNS #
City
New Haven
State
CT
Country
United States
Zip Code
06520