Electric charges of positrons and antiprotons

Abstract

Tests of the electric charges carried by the positron and antiproton are derived from recent measurements of the cyclotron frequencies of these particles, and from the spectroscopy of exotic atoms in which they are constituents.There has recently been considerable interest in highprecision tests of the equality of particle and antiparticle masses that is required by CPT symmetry [1,2]. A method that has been applied to electrons and positrons [3] and protons and antiprotons [l] utilizes the cyclotron frequency, (o-qB/m, of a particle of mass m and charge q in a magnetic field B. Indeed, comparisons of the cyclotron frequencies of electrons and protons (or ions that contain these particles as constituents) in the same magnetic field are regarded as tests of the particles' mass ratios, because there is independent information that the magnitudes of the electron and proton charges are equal. However, there are no analogous tests for the charges of electrons and positrons or protons and antiprotons. Therefore, cyclotron frequency comparisons for these particle-antiparticle pairs should strictly be regarded as comparisons of the particles' charge-to-mass ratios [4,5], unless the additional assumptions of either charge quantization or CPT symmetry for particle-antiparticle charges are made. These assumptions involve concepts that are as fundamental as the equality of particle and antiparticle masses and hence deserve their own independent tests. In this Letter we shall derive tests of the positron and antiproton charges by combining precision measurements of their cyclotron frequencies with spectroscopic measurements on positronium and antiprotonic atoms. Then we shall discuss how these tests could be improved with experiments on antihydrogen. We start by reviewing the existing experimental tests of charge quantization.

Forty years of antiprotons

“…These methods seem out of the question for antiprotons, although an atomic-beam experiment has been suggested that has something in common with both (1) and (3) Deutch, 1992). A beam of antihydrogen atoms would be injected between the plates of a parallel-plate capacitor.…”

“…(22) is small. The deflection of the beam is given by (Deutch, 1992) (Geer et al, 1994). From experiment T861 at Fermilab.…”

“…Since 1990, the method has been refined and the relative errors reduced by a further factor of 40, bringing the ratio to Rϭ1ϩ(1.5Ϯ1.1)ϫ10 Ϫ9 . We stress, however, that the equality of the charge-to-mass ratio on the ppb level does not prove mass equality at the same level, as the equality of proton and antiproton electric charge has only been established with considerably lower precision, either directly or (Hughes and Deutch, 1992) by including Rydberg energy determinations with the cyclotron frequency measurements as described in Sec. VI.B.3.…”

Detection of Trapped Antihydrogen

“…Several example comparisons include: electron/positron mass [3], charge [4], and gyromagnetic ratio [5];…”

“…B.1(c)). The total depletion width, w, is given as (assuming that potential due to charge diffusion is small) [110], 4) where V b is the reverse bias applied, is the dielectric constant of the medium (11.9 for silicon), and N a and N d are the acceptor and donor concentrations, respectively. For example, with doping concentrations of N a = N d = 10 13 cm −3 and an applied reverse bias of V b = 65 V, the depletion width is w 300 µm.…”