Speaker
Description
The observed dominance of matter over antimatter motivates precision comparisons of particles and antiparticles, where even extremely small differences could signal physics beyond the Standard Model. Antihydrogen, a positron bound to an antiproton, offers an exceptionally clean atomic system because its transition frequencies can be measured precisely and compared with the corresponding hydrogen transitions. In the ALPHA experiment at CERN, antihydrogen atoms are magnetically trapped and probed using microwave spectroscopy, enabling measurements of ground-state hyperfine transitions in a magnetic field and providing sensitive tests of Charge-Parity-Time (CPT) symmetry and Lorentz invariance.
We outline an analysis framework based on the Standard-Model Extension (SME), which parametrizes possible CPT- and Lorentz-violating effects as small background couplings to particle properties such as spin. These couplings can produce tiny, orientation- and time-dependent shifts in transition frequencies, including signatures that vary with sidereal time due to Earth’s rotation. Because trapped antihydrogen spectroscopy must be performed in the magnetic trapping field, hyperfine analyses often combine transition frequencies to suppress common sensitivity to magnetic-field variations; however, such combinations can also cancel leading spin-dependent SME contributions. We therefore focus on the SME interpretation of individual ground-state positron spin-flip transitions measured in ALPHA, treating each transition as an independent probe of spin-dependent symmetry-violating effects.
Using a time series of measured transition frequencies together with magnetic-field diagnostics and experimental geometry, we search for sidereal modulations and other orientation-dependent SME signatures while quantifying dominant systematics such as magnetic-field drifts. The goal is to use existing ALPHA datasets and future measurements to set improved antimatter-based bounds on spin-dependent SME parameters and compare them with matter-based limits.
| Keyword-1 | Antihydrogen |
|---|---|
| Keyword-2 | Hyperfine spectroscopy |
| Keyword-3 | Lorentz and CPT symmetry (SME) |