Session J06: Low-Energy Precision Tests of the Standard Model

A precision measurement of the electron's electric dipole moment using trapped molecular ions

Alongside high energy colliders, precision tests of fundamental symmetries in low energy systems present a complementary path toward evidence for microscopic physics beyond the Standard Model of particle interactions (SM). Among these, permanent electric dipole moment searches are promising, due to the strong motivation to search for sources of charge-parity (CP) symmetry violation beyond the SM, and due to their very low background within the SM. I will describe a recent measurement of the electron's electric dipole moment (eEDM, d$_{\mathrm{e}})$ using $^{\mathrm{180}}$Hf$^{\mathrm{19}}$F$^{\mathrm{+}}$ molecular ions confined in a radiofrequency trap, and our progress towards a second generation measurement with an order of magnitude higher sensitivity. In addition to providing confirmation of the present upper limit on d$_{\mathrm{e}}$, it is the first eEDM measurement to demonstrate coherence times $>$1 second in a molecular system \textemdash a feature that will be valuable in the highest precision future eEDM searches.\\ \\In collaboration with: Daniel N. Gresh, Tanya S. Roussy, Kia Boon Ng, Yan Zhou, Yuval Shagam, Jun Ye, and Eric A. Cornell; JILA, NIST and University of Colorado, and Department of Physics, University of Colorado   

Challenging the Standard Model: High-Precision Comparisons of the Fundamental Properties of Protons and Antiprotons

The Baryon Antibaryon Symmetry Experiment (BASE-CERN) at CERN's antiproton decelerator facility is aiming at high-precision comparisons of the fundamental properties of protons and antiprotons, such as charge-to-mass ratios, magnetic moments and lifetimes. Such experiments provide sensitive tests of the fundamental charge-parity-time invariance in the baryon sector. BASE was approved in 2013 and has measured since then, utilizing single-particle multi-Penning-trap techniques, the antiproton-to-proton charge-to-mass ratio with a fractional precision of 69 p.p.t., as well as the antiproton magnetic moment with fractional precisions of 0.8 p.p.m. and 1.5 p.p.b., respectively. At our matter companion experiment BASE-Mainz, we have performed proton magnetic moment measurements with fractional uncertainties of 3.3 p.p.b. and 0.3 p.p.b. By combining the data of both experiments we provide a baryon-magnetic-moment based CPT test g$_{\mathrm{pbar}}$/g$_{\mathrm{p\thinspace }}=$ 1.000 000 000 2(15), which improves the uncertainty of previous experiments by more than a factor of 3000. A unique antiproton reservoir trap used in BASE, furthermore allows us to set constraints on directly measured antiproton lifetime. Our current value t$_{\mathrm{p}}$\textgreater 10.2a improves previous best limits by a factor of 30. In this talk I will review the achievements of BASE and focus on recent developments which will allow us to further reduce our measurement uncertainties.   

Precision microwave measurements of n=2 states in simple atoms: Determination of the fine-structure constant and the charge radius of the proton

A high-precision measurement of the fine structure of the n=2 states of atomic hydrogen is being performed as a test of both quantum electrodynamics and to determine the charge radius of the proton. The proton radius has been a matter of great interest in the past years, since measurements made with muonic hydrogen show a large disagreement with those obtained using electrons. A precision measurement of the helium n=2 fine structure also tests quantum electrodynamics, but may additionally be used to determine the fine-structure constant.