Speaker
Description
The BASE collaboration, situated at CERN's Antiproton Decelerator facility, uses Penning traps to test the Charge-Parity-Time (CPT) symmetry by measuring the fundamental properties of protons and antiprotons to ultra-high precision [1].
One such property which can be directly measured in Penning traps is the proton-to-antiproton charge-to-mass ratio, $\left(q/m_{\rm{p}}\right)/\left(q/m_{\bar{\rm{p}}}\right)$. Here, the free-cyclotron frequency, $\omega_{c} = qB_{0} / m_{\bar{\rm{p}},\rm{H}^{-}}$, of both $\bar{\rm{p}}$ and $\rm{H}^{-}$ are compared – with the $\rm{H}^{-}$ serving as a proxy for the proton. $\omega_{c}$ is determined by measuirng the three eigen-frequencies, $\omega_{-,z,+}$, of the trapped particle and applying an invariance theorem; $\omega_{c}^{2} = \omega_{-}^{2} + \omega_{z}^{2} + \omega_{+}^{2}$. The BASE collaboration has previously measured this quantity to a precision of $69$ $\rm{ppt}$ [4]. This result is consistent with CPT invariance. The proton-to-antiproton charge-to-mass ratio also serves as a test of the weak equivalence principle and can be used to constrain the gravitational anomaly parameter, $\alpha_{g}$. The BASE collaboration has constrained this parameter to $\left| \alpha_{g} - 1\right| < 8.7 \times 10^{-7} $ in the case of baryonic matter.
During the current measurement campaign performed by BASE, several technical and methodological improvements have recently been made. The implementation of a new superconducting modified-cyclotron frequency detection system allows direct measurements of $\omega_{+}$, for both $\bar{\rm{p}}$ and $\rm{H}^{-}$. This contrasts with previous measurements where $\omega_{+}$ is measured indirectly by coupling axial and modified-cyclotron modes [4]. The addition of a resonance-frequency tuneable circuit to the axial detection system, in conjunction with significant improvement to the magnetic field homogeneity, has eliminated the principal systematic error of the previous $69$ $\rm{ppt}$ result [4]. These new implementations allow the $69$ $\rm{ppt}$ CPT invariance test to be improved upon, and measuring the proton-to-antiproton charge-to-mass ratio at different points in the sidereal year allow improved constraints on the gravitational anomaly parameter.
In this talk preliminary results of the recent proton-to-antiproton charge-to-mass ratio charge to mass ratio campaign will be presented, along with details of the methodologies and improvements used to achieve them.
[1] G. Gabrielse et al., Phys. Rev. Lett., 82, (1999), 3198-3201
[2] G. Schneider et al., Science, 358, (2017), 1081-1084
[3] C. Smorra et al., Nature, 550, (2017), 371-374
[4] S. Ulmer et al., Nature, 524, (2015), 196-199
