H. Higaki

A source of antihydrogen for in-flight hyperfine spectroscopy

Antihydrogen, a positron bound to an antiproton, is the simplest antiatom. Its counterpart—hydrogen—is one of the most precisely investigated and best understood systems in physics research. High-resolution comparisons of both systems provide sensitive tests of CPT symmetry, which is the most fundamental symmetry in the Standard Model of elementary particle physics. Any measured difference would point to CPT violation and thus to new physics. Here we report the development of an antihydrogen source using a cusp trap for in-flight spectroscopy. A total of 80 antihydrogen atoms are unambiguously detected 2.7 m downstream of the production region, where perturbing residual magnetic fields are small. This is a major step towards precision spectroscopy of the ground-state hyperfine splitting of antihydrogen using Rabi-like beam spectroscopy.

Wall and Temperature Effects on Electrostatic Oscillations of Spheroidal Non-neutral Electron Plasmas in the Multi-Ring Electrode Trap

Electrostatic oscillations of spheroidal non-neutral electron plasmas are experimentally investigated with the multiring electrode trap which provides an electrostatic quadrupole potential with a long axial extent and enables confinement of plasmas with large aspect ratios. The frequencies of axial modes l = 2 and 3 of trapped plasmoids shifts upwards from those predicted by Dubins cold plasma theory for the free boundary case, mainly due to the image charges induced on the conducting electrodes. These frequencies continue to increase as the plasma temperature is increased from 0.03 eV to 1.5 eV by rf heating. This temperature dependence can be interpreted as a change in the dielectric tensor caused by the temperature increase.

The ASACUSA antihydrogen and hydrogen program: results and prospects

The goal of the ASACUSA-CUSP collaboration at the Antiproton Decelerator of CERN is to measure the ground-state hyperfine splitting of antihydrogen using an atomic spectroscopy beamline. A milestone was achieved in 2012 through the detection of 80 antihydrogen atoms 2.7 m away from their production region. This was the first observation of ‘cold’ antihydrogen in a magnetic field free region. In parallel to the progress on the antihydrogen production, the spectroscopy beamline was tested with a source of hydrogen. This led to a measurement at a relative precision of 2.7×10−9 which constitutes the most precise measurement of the hydrogen hyperfine splitting in a beam. Further measurements with an upgraded hydrogen apparatus are motivated by CPT and Lorentz violation tests in the framework of the Standard Model Extension. Unlike for hydrogen, the antihydrogen experiment is complicated by the difficulty of synthesizing enough cold antiatoms in the ground state. The first antihydrogen quantum states scan at the entrance of the spectroscopy apparatus was realized in 2016 and is presented here. The prospects for a ppm measurement are also discussed. This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.

Electrons Confined with an Axially Symmetric Magnetic Mirror Field

Low energy non‐neutral electron plasmas were confined with an axially symmetric magnetic mirror field and an electrostatic potential to investigate the basic confinement properties of a simple magnetic mirror trap. As expected the confinement time became longer as a function of the mirror ratio. The axial electrostatic oscillations of a confined electron plasma were also observed. Obtained results suggested an improved scheme to accumulate low energy charged particles with the use of a magnetic mirror field, which would enable the investigation of electron‐positron plasmas.

Determination of Transverse Distributions of Ion Plasmas Confined in a Linear Paul Trap by Imaging Diagnostics

This paper presents a diagnostic method to measure the transverse distribution of an ion plasma confined in a linear Paul trap with a relatively large number of ions (~107). The distribution of the plasma extracted from the trap is converted to a luminosity distribution using a microchannel plate (MCP) with a phosphor screen, and it is recorded with a charge-coupled device (CCD) camera. The linearity of the imaging system, which is the basis of the quantitative analyses, is ensured by correcting the saturation of MCP gain over a wide range of ion number. The correspondence between the density profile of an ion plasma in the trap and that at the MCP surface is examined by numerical simulation. The density profile in the trap can be reconstructed accurately from the observed luminosity distribution based on the linearity and the correspondence. Moreover, the transverse temperature and the tune depression can also be determined from the observed transverse density profile. The detailed measurement of the transverse plasma distribution is essential for the experimental study of various collective effects in space-charge-dominated beams using the ion trap. As an example of observations by the imaging diagnostic system, we also demonstrate the shrinking of the transverse plasma distribution by buffer-gas cooling.

Towards measuring the ground state hyperfine splitting of antihydrogen – a progress report

We report the successful commissioning and testing of a dedicated field-ioniser chamber for measuring principal quantum number distributions in antihydrogen as part of the ASACUSA hyperfine spectroscopy apparatus. The new chamber is combined with a beam normalisation detector that consists of plastic scintillators and a retractable passivated implanted planar silicon (PIPS) detector.

The development of the superconducting double cusp magnet for intense antihydrogen beams

We have developed a superconducing double cusp magnet for the production of polarized intense antihydrogen atomic beams which are used to make microwave spectroscopy of a ground state hyperfine transition to test the CPT symmetry. The detail of specification and the focusing performance of the magnet will be presented.

The development of the antihydrogen beam detector and the detection of the antihydrogen atoms for in-flight hyperfine spectroscopy

We have been developing ground-state antihydrogen atomic beams to test CPT symmetry via in-flight hyperfine spectroscopy. A new antihydrogen beam detector has been developed. The overview of the experiment, the detail of the detector and latest results will be presented.

Positron accumulation and manipulation for antihydrogen synthesis

Our group ASACUSA-MUSASHI has established an efficient way for accumulating antiprotons in the cusp trap, a combination of an anti-Helmholz superconducting coil and a multi-ring electrode trap. The last piece for synthesizing antihydrogens in the cusp trap is positron. We have developed a compact system to effectively accumulate positrons based on N2 gas-buffer scheme with a specially designed high precision cylindrical multi-ring electrode trap. Millions of positrons were accumulated in the pre-accumulator just using polycrystalline tungsten moderators. The accumulated positrons were transported as a pulsed beam via three guiding coils and caught in the cusp trap under cryogenic and ultra high vacuum conditions without serious loss. Confinement of two kinds of numerous antiparticles, e.g., 108 positrons and 107 antiprotons, in the cusp trap becomes feasible.

A tandem linear Paul trap as an ion source

Argon ions were produced by electron impact ionization in a linear Paul trap and confined there directly. The ions with a specific charge state (Ar+ and Ar2+ in this report) were successfully extracted as a pulsed beam by using another linear Paul trap as a mass filter. In principle, this technique is applicable for various highly charged ions generated and trapped in an ion source. The tandem linear Paul trap described here can also be employed, with the help of laser cooling, to produce nano-ion beams.