Diagnosing Antihydrogen Energy Distributions using Spatio-temporal Annihilation Patterns

Abstract

Abstract Precision measurements of the fundamental properties of trapped antihydrogen in the ALPHA experiment at CERN require an accurate determination of the antihydrogen energy distribution. We introduce a new diagnostic technique, termed Spatio-Temporal Annihilation Mapping (STAM), which measures this distribution by exploiting the dynamics of antihydrogen in adiabatically time-varying magnetic fields. By analyzing the spatial and temporal patterns of annihilations recorded during adiabatic release from magnetic confinement and comparing them with detailed simulations, we infer the underlying energy distributions. STAM enables the simultaneous measurement of axial and transverse energy components, achieving a relative precision of approximately 10% over a mean energy range of ∼10-100 mK in the ALPHA trap. The technique is applied to both uncooled and laser-cooled antihydrogen populations, with results benchmarked against established laser-based diagnostics. While laser-based methods provide high-resolution measurements of the transverse energy and limited sensitivity to the axial component, an accurate determination of the axial energy remains challenging. In addition to complementing existing techniques, STAM is expected to access energy regimes that are currently inaccessible to laser-based diagnostics due to intrinsic limitations of those methods. These capabilities make STAM broadly applicable to future high-precision spectroscopic and gravitational studies with antihydrogen. Furthermore, STAM provides a novel probe of off-axis magnetic field structures, addressing a critical gap in current magnetometry techniques within the ALPHA experiment.