An experimental limit on the charge of antihydrogen

Abstract

The properties of antihydrogen are expected to be identical to those of hydrogen, and any differences would constitute a profound challenge to the fundamental theories of physics. The most commonly discussed antiatom-based tests of these theories are searches for antihydrogen-hydrogen spectral differences (tests of CPT (charge-parity-time) invariance) or gravitational differences (tests of the weak equivalence principle). Here we, the ALPHA Collaboration, report a different and somewhat unusual test of CPT and of quantum anomaly cancellation. A retrospective analysis of the influence of electric fields on antihydrogen atoms released from the ALPHA trap finds a mean axial deflection of 4.1±3.4 mm for an average axial electric field of 0.51 V mm−1. Combined with extensive numerical modelling, this measurement leads to a bound on the charge Qe of antihydrogen of Q=(−1.3±1.1±0.4) × 10−8. Here, e is the unit charge, and the errors are from statistics and systematic effects.

Observation of the 1S–2S transition in trapped antihydrogen

“…This feat was later repeated [7][8][9] , and in 2010 antihydrogen was successfully trapped 3 to facilitate its study. It was subsequently shown that antiatoms could be held 4 for up to 1,000 s, and various measurements have been performed on antihydrogen in the context of tests of CPT symmetry [10][11][12] or gravitational studies 13 .…”

Axial to transverse energy mixing dynamics in octupole-based magnetostatic antihydrogen traps

“…For example, the ALPHA external solenoid is not precisely fixed with respect to the magnetic trap, and B sol could be tilted with respect to the trap axis. This tilt is less than 2 mrad in the ALPHA system [23]. Figure 15(a) shows that such tilts increase the mixing fraction, but that the effect is small.…”

“…Most of the antiatoms with energy above the trapping depth escape quickly, but simulations find that a few 'quasi-bound' antiatoms are slow to find an energetically-allowed escape 'hole', and remain trapped for substantial periods of time [21,22]. Some aspects of this choice of distribution have been validated by comparing simulation and experimental results [3,18,22,23].…”

On the formation of trappable antihydrogen

“…Recent years have seen major experimental advances in the production and trapping of antihydrogen,H , the positron (e + )−antiproton (p) bound state (see e.g., the reviews [1][2][3][4]), which have facilitated the first determinations of some of its properties [5][6][7][8][9]. Indeed, such measurements were only feasible due to the capability to hold ground stateH in a magnetic minimum neutral atom trap for periods of many minutes [10][11][12] to allow interaction with applied electric fields, or microwave or laser radiation.…”