Proton-to-Electron Mass Variation
Context - the Search for the Theory of Everything
At its heart, fundamental physics has a problem: general relativity describing heavy objects and quantum mechanics (generalised to the standard model of matter) describing small objects do not fit together as scientific theories and so there is no consistent and experimentally established theory for describing heavy small objects like black holes and the Big Bang. The Large Hadron Collider, though finding the long-anticipated Higgs boson, has not yet produced new physics; to the contrary, many theories like supersymmetry are looking less and less likely. Therefore, alternate experiments are imperative. One such experiment involves measuring whether the proton-to-electron mass ratio has varied over time or over space. Note that though this is a fundamental constant in our current understanding, many theories beyond the standard model predict variations. Measuring this constant probes these theories just like the pivotal Michelson-Morley experiment measures the speed of light in the 19th century (recall that this experiment led to special and general relativity).
Experimental Tests
Spectroscopic measurements are the most accurate measurement humans can currently make and thus ideal for measuring proton-to-electron mass variation. Theoretical support is vital in connecting an change in the observed spectroscopic measurement to a variation in this mass ratio. This project involves the identification of the molecule and spectral transitions that are likely to deliver the highest sensitivity measurement of proton-to-electron mass variation.
My Contribution
This project will theoretically probe the spectral sensitivity to mass ratio variation of a significant number of molecules, ranging from open-shell diatomic to polyatomic molecules. The sensitivity of the measurement is limited by the experimental ability to detect the frequency of a spectral line; this is controlled by the inherent properties of the spectral line (width and intensity) as well the the instrument uncertainties. The width of the spectral line is affected by radiative lifetime and the temperature to which the molecule can be cooled (which affects transit time broadening). This research will differ from previous studies by first establishing a comprehensive set of criteria for a good target transition (for both astronomy and laboratory experiments), by looking at a large number of molecules and by focusing jointly on relative and absolute sensitivity of the transition frequency to variation in proton-to-electron mass ratio.
Students
Hoa Klinkesorn Nguyen, Masters Student,UCL, 2015-2016.
Study of Sensitivity of Spectral Transitions in Double-Welled Potentials to Variation in Proton- to-Electron Mass Ratio
Aden Lam, Summer Student, UCL, 2015.
Study of Sensitivity of Spectral Transitions in Single-Well Potentials to Variation in Proton-to-Electron Mass Ratio
Collaborators
Victor Flambaum, University of New South Wales, Australia
Theoretical Physicist, specialising in tests of fundamental physics.
Mike Tarbutt, Imperial College London, UK
Experimental Physicist in High Precision Molecular Science, e.g. Laser Cooling of Molecules.