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The Standard Model (SM) of particle physics is both incredibly successful andglaringly incomplete. Among the questions left open is the striking imbalanceof matter and antimatter in the observable universe which inspires experimentsto compare the fundamental properties of matter/antimatter conjugates with highprecision. Our experiments deal with direct investigations of the fundamentalproperties of protons and antiprotons, performing spectroscopy in advancedcryogenic Penning-trap systems. For instance, we compared the proton/antiprotonmagnetic moments with 1.5 ppb fractional precision, which improved uponprevious best measurements by a factor of >3000. Here we report on a newcomparison of the proton/antiproton charge-to-mass ratios with a fractionaluncertainty of 16ppt. Our result is based on the combination of fourindependent long term studies, recorded in a total time span of 1.5 years. Weuse different measurement methods and experimental setups incorporatingdifferent systematic effects. The final result,$-(q/m)_{\mathrm{p}}/(q/m)_{\bar{\mathrm{p}}}$ = $1.000\,000\,000\,003 (16)$,is consistent with the fundamental charge-parity-time (CPT) reversalinvariance, and improves the precision of our previous best measurement by afactor of 4.3. The measurement tests the SM at an energy scale of$1.96\cdot10^{-27}\,$GeV (C$.$L$.$ 0.68), and improves 10 coefficients of theStandard Model Extension (SME). Our cyclotron-clock-study also constrainshypothetical interactions mediating violations of the clock weak equivalenceprinciple (WEP$_\text{cc}$) for antimatter to a level of $|\alpha_{g}-1| < 1.8\cdot 10^{-7}$, and enables the first differential test of the WEP$_\text{cc}$using antiprotons \cite{hughes1991constraints}. From this interpretation weconstrain the differential WEP$_\text{cc}$-violating coefficient to$|\alpha_{g,D}-1|<0.030$.

A 16 Parts per Trillion Comparison of the Antiproton-to-Proton q/m Ratios