Speaker
Description
Even though the standard model has been successful in predicting and describing subatomic phenomena, it requires symmetry under charge, particle and time inversion and can thus not explain certain cosmological observations. A difference in the fundamental properties between matter and antimatter would break CPT invariance, will further our understanding of the shortcomings of the standard model, and could potentially explain aspects of the excess of matter over antimatter. The BASE experiment is testing CPT invariance in the baryonic sector by comparing the ratios of charge-to-mass ratios and the magnetic moments of protons (p) and the antiprotons (p).
BASE uses advanced Penning-trap-systems to confine single particles inside an electrostatic potential well with a constant magnetic field [1]. By measuring the cyclotron frequencies $ω_c = q/m · B$ of a proton and an antiproton, their charge-to-mass ratio can be determined. Calculating the relative charge to mass ratio eliminates the dependence on the magnetic field and allows specifying it to a fractional precision of 16 p.p.t. [2]. By measuring the Larmor frequency ωL of both particles as well,
the g-factors $g = 2μ/μ_N = 2ω_L/ω_c$ can be specified to a fractional precision of 0.3 p.p.b. and 1.5 p.p.b. [3, 4].
$(q_{\overline{p}}/m_{\overline{p}})/(q_p/m_p) = −ω_{c,{\overline{p}}}/ω_{c,p} = −1 ± 1.6 · 10^{−11}$
$(ω_{L,{\overline{p}}}/ω_{c,{\overline{p}}})/(ω_{L,p}/ω_{c,p}) = g_{{\overline{p}}}/g_p = −1 ± 1.6 · 10^{−9}$
Since the start of the BASE experiment program, multiple improvements of the applied frequency measurement schemes have been made, decreasing the uncertainties of the measured fundamental quantities by multiple orders of magnitude. With direct frequency measurements limited by their
$T^{−1/2}$ scaling with measurement time, the next step is the implementation of phase information [5] in
the determination of the modified cyclotron frequency to reach a $T^{−1}$ scaling.
I will give an overview about BASE, the current frequency measurement schemes used, and the particular limitations and problems that we face using them. I will introduce the concept of phase sensitive frequency measurements in the context of BASE, and discuss their advantages and new
inherent precision limits.
[1] C. Smorra et al. “BASE–the baryon antibaryon symmetry experiment”. In: The European Physical Journal Special
Topics 224.16 (2015), pp. 3055–3108.
[2] M. J. Borchert et al. “A 16-parts-per-trillion measurement of the antiproton-to-proton charge–mass ratio”. In:
Nature 601.7891 (2022), pp. 53–57. doi: 10.1038/s41586-021-04203-w.
[3] Georg Schneider et al. “Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision”.
In: Science 358.6366 (2017), pp. 1081–1084.
[4] C Smorra et al. “A parts-per-billion measurement of the antiproton magnetic moment”. In: Nature 550.7676 (2017),
pp. 371–374.
[5] E. A. Cornell et al. “Mode coupling in a Penning trap: π pulses and a classical avoided crossing”. In: Phys. Rev. A
41 (1 1990), pp. 312–315. doi: 10.1103/PhysRevA.41.312.
