A hydrogen beam to characterize the ASACUSA antihydrogen hyperfine spectrometer

The antihydrogen programme of the ASACUSA collaboration at the antiproton decelerator of CERN focuses on Rabi-type measurements of the ground-state hyperfine splitting of antihydrogen for a test of the combined Charge-Parity-Time symmetry. The spectroscopy apparatus consists of a microwave cavity to drive hyperfine transitions and a superconducting sextupole magnet for quantum state analysis via Stern-Gerlach separation. However, the small production rates of antihydrogen forestall comprehensive performance studies on the spectroscopy apparatus. For this purpose a hydrogen source and detector have been developed which in conjunction with ASACUSA's hyperfine spectroscopy equipment form a complete Rabi experiment. We report on the formation of a cooled, polarized, and time modulated beam of atomic hydrogen and its detection using a quadrupole mass spectrometer and a lock-in amplification scheme. In addition key features of ASACUSA's hyperfine spectroscopy apparatus are discussed.

A hydrogen beam to characterize the ASACUSA antihydrogen hyperfine spectrometer

The antihydrogen program of the ASACUSA collaboration at the antiproton decelerator of CERN focuses on Rabi-type measurements of the ground-state hyperfine splitting of antihydrogen for a test of the combined Charge\u2013Parity\u2013Time symmetry. The spectroscopy apparatus consists of a microwave cavity to drive hyperfine transitions and a superconducting sextupole magnet for quantum state analysis via Stern\u2013Gerlach separation. However, the small production rates of antihydrogen forestall comprehensive performance studies on the spectroscopy apparatus. For this purpose a hydrogen source and detector have been developed which in conjunction with ASACUSA's hyperfine spectroscopy equipment form a complete Rabi experiment. We report on the formation of a cooled, polarized, and time modulated beam of atomic hydrogen and its detection using a quadrupole mass spectrometer and a lock-in amplification scheme. In addition key features of ASACUSA's hyperfine spectroscopy apparatus are discussed

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 \u2018cold\u2019 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 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 \u2018Antiproton physics in the ELENA era\u2019

Cyclotron cooling to cryogenic temperature in a Penning-Malmberg trap with a large solid angle acceptance

Magnetized nonneutral plasma composed of electrons or positrons couples to the local microwave environment via cyclotron radiation. The equilibrium plasma temperature depends on the microwave energy density near the cyclotron frequency. Fine copper meshes and cryogenic microwave absorbing material were used to lower the effective temperature of the radiation environment in ASACUSA's Cusp trap, resulting in significantly reduced plasma temperature

Reducing the background temperature for cyclotron cooling in a cryogenic Penning-Malmberg trap

Magnetized nonneutral plasma composed of electrons or positrons couples to the local microwave environment via cyclotron radiation. The equilibrium plasma temperature depends on the microwave energy density near the cyclotron frequency. Fine copper meshes and cryogenic microwave absorbing material were used to lower the effective temperature of the radiation environment in ASACUSA's Cusp trap, resulting in significantly reduced plasma temperature. (C) 2022 Author(s).All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY)license (http://creativecommons.org/licenses/by/4.0/)

Atomic Spectroscopy and Collisions Using Slow Antiprotons \\ ASACUSA Collaboration

ASACUSA (\underline{A}tomic \underline{S}pectroscopy \underline{A}nd \underline{C}ollisions \underline{U}sing \underline{S}low \underline{A}ntiprotons) is a collaboration between a number of Japanese and European research institutions, with the goal of studying bound and continuum states of antiprotons with simple atoms.\\ Three phases of experimentation are planned for ASACUSA. In the first phase, we use the direct $\overline{p}$ beam from AD at 5.3 MeV and concentrate on the laser and microwave spectroscopy of the metastable antiprotonic helium atom, $\overline{p}$He$^+$, consisting of an electron and antiproton bound by the Coulomb force to the helium nucleus. Samples of these are readily created by bringing AD antiproton beam bunches to rest in helium gas. With the help of techniques developed at LEAR for resonating high precision laser beams with antiproton transitions in these atoms, ASACUSA achieved several of these first-phase objectives during a few short months of AD operation in 2000. Six atomic transitions of the metastable antiprotonic helium atom were thereby detected, three of which had not previously been observed. They included two transitions in the UV region of the spectrum. If we assume CPT invariance between the properties of the proton and the antiproton, as the theoretical calculations of transition frequencies do, the agreement is a signature of the excellence of theoretical treatments and calculation techniques of three-body Coulomb system including QED corrections. If, on the other hand, we take the calculated values to be correct, the agreement gives a stringent test of the fundamental constants of the antiproton and therefore tests the CPT theorem. Taking the second point of view, the results from the year 2000 together constrain any difference between the antiproton and proton charges and masses by a further factor of eight beyond the limits obtained by our PS205 experiments at LEAR.\\ The year 2000 also saw the first success of the ASACUSA triple-resonance laser/ microwave experiment. In this, both laser and microwave beams are to be used to measure the peculiar hyperfine structure of $\overline{p}$He$^+$, associated with the interaction of the electron spin magnetic moment with the orbital magnetic moment of the antiproton.\\ In phase 2 experiments, we add an RFQ linear decelerator (RFQD), which decelerates antiprotons from 5.3 MeV to few tens of keV. By enabling us to stop the antiprotons in very low density gas targets, this makes it possible to study in detail the imperfectly understood processes by which antiprotonic atoms are created. It also allows us to measure the antiproton's specific energy loss dE/dx in a variety of materials. After a test period with 5 MeV protons spent in a proton beam in Aarhus, the RFQD was installed in the AD beam line in November, and reached its design energy in the tens of keV range, with deceleration efficiency approaching the expected value of 45$\%$. The RFQD beam was then used to produce extensive new data on the stopping power of carbon and gold for antiprotons in the crucial unexplored region between 60 keV and 8 keV.\\ In phase 3, a multielectrode antiproton trap, another powerful tool for studying the antiproton, will be placed downstream of the RFQD. At the time of writing (March 2001), this had been assembled in the AD beam line after extensive testing in Tokyo. Antiprotons will be captured and cooled (by collisions with electrons) in the trap, and then extracted from it at and below $\sim 1$ keV (eventually down to $\sim 10$ eV). Such ultra-low-energy beams have hitherto been unavailable. They will allow us to produce antiprotonic atoms at such low target pressures that they are almost unperturbed by further collisions with target atoms. This will permit study of their production mechanisms in still closer detail, and the performance of extremely high precision spectroscopy.\