Assuming hydrogen is charge neutral, CPT invariance demands that antihydrogen also be charge neutral. Quantum anomaly cancellation also demands that antihydrogen be charge neutral. Standard techniques based on measurements of macroscopic quantities o
f atoms cannot be used to measure the charge of antihydrogen. In this paper, we describe how the application of randomly oscillating electric fields to a sample of trapped antihydrogen atoms, a form of stochastic acceleration, can be used to place experimental limits on this charge.
Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the mag
netic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilated. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly-identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.
Charges in cold, multiple-species, non-neutral plasmas separate radially by mass, forming centrifugally-separated states. Here, we report the first detailed measurements of such states in an electron-antiproton plasma, and the first observations of t
he separation dynamics in any centrifugally-separated system. While the observed equilibrium states are expected and in agreement with theory, the equilibration time is approximately constant over a wide range of parameters, a surprising and as yet unexplained result. Electron-antiproton plasmas play a crucial role in antihydrogen trapping experiments.
We have demonstrated production of antihydrogen in a 1$,$T solenoidal magnetic field. This field strength is significantly smaller than that used in the first generation experiments ATHENA (3$,$T) and ATRAP (5$,$T). The motivation for using a smaller
magnetic field is to facilitate trapping of antihydrogen atoms in a neutral atom trap surrounding the production region. We report the results of measurements with the ALPHA (Antihydrogen Laser PHysics Apparatus) device, which can capture and cool antiprotons at 3$,$T, and then mix the antiprotons with positrons at 1$,$T. We infer antihydrogen production from the time structure of antiproton annihilations during mixing, using mixing with heated positrons as the null experiment, as demonstrated in ATHENA. Implications for antihydrogen trapping are discussed.
We report results from a novel diagnostic that probes the outer radial profile of trapped antiproton clouds. The diagnostic allows us to determine the profile by monitoring the time-history of antiproton losses that occur as an octupole field in the
antiproton confinement region is increased. We show several examples of how this diagnostic helps us to understand the radial dynamics of antiprotons in normal and nested Penning-Malmberg traps. Better understanding of these dynamics may aid current attempts to trap antihydrogen atoms.
Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as te
n, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.
