Please join us Monday, July 14 for a talk from Cornell group visitor Heleen Mulder. Heleen is a PhD student working on theoretical particle physics with Jordy de Vries at Nikhef in Amsterdam and a member of the NLeEDM collaboration.
Abstract: The experimental search for CP violation in paramagnetic atomic and molecular systems has made impressive progress in recent years. This has led to strong upper limits on the electron electric dipole moment. Interestingly, the same measurements can be used to constrain hadronic sources of CP violation, through CP-violating interactions between the electrons and the nucleus. In this talk, I will focus on one specific source of hadronic CP violation: the QCD theta term. I will sketch calculations of the relevant CP-violating electron-nucleus interactions, carried out in an effective field theory formalism. Based on this work, we arrive at a novel upper bound on the theta parameter. While currently two orders of magnitude less stringent than the upper bound from the neutron EDM, further experimental improvements on the paramagnetic EDM side could soon make this bound competitive. If and when EDM experiments start yielding non-zero results, these independent bounds will be crucial to disentangle the possible underlying CP-violating sources. Aside from the QCD theta term, the methods presented in this talk can also be used to determine contributions from other hadronic sources of CP violation to paramagnetic EDMs.