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International Conference on Low Energy Antiproton Physics (LEAP)

Antihydrogen Synthesis in a Double-Cusp Trap

N. Kuroda, M. Tajima, B. Radics, Pierre Dupré, Y. Nagata, C. Kaga, Yasuyuki Kanai, Marco Leali, Evandro Lodi Rizzini, V. Mascagna, Takuya Matsudate, H. Breuker, H. Higaki, Y. Matsuda, S. Ulmer, L. Venturelli, Y. Yamazaki

Published Nov 23, 2017• 5 citations
Publisher

Abstract

The ASACUSA CUSP experiment plans a high precision spectroscopy of the ground-state hyperfine splitting of antihydrogen to test CPT symmetry.To perform this, a Rabi-like antiatomic beam method has been developed with a novel double-cusp trap.Antihydrogen atoms were synthesized in the double-cusp trap by directly injecting antiprotons from an accumulation trap into a positron plasma.By adjusting the energy difference between the incoming antiproton beam and the positron plasma, a high-rate production of antihydrogen atoms was observed.

DOI
10.7566/jpscp.18.011009

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The ASACUSA CUSP experiment plans a high precision spectroscopy of the ground-state hyperfine splitting of antihydrogen to test CPT symmetry.To perform this, a Rabi-like antiatomic beam method has been developed with a novel double-cusp trap.Antihydrogen atoms were synthesized in the double-cusp trap by directly injecting antiprotons from an accumulation trap into a positron plasma.By adjusting the energy difference between the incoming antiproton beam and the positron plasma, a high-rate production of antihydrogen atoms was observed.
The purpose of cold antihydrogen research is briefly reviewed together with the latest developments of manipulating antihydrogen atoms. Two major progresses last year were the trapping of antihydrogen atoms in a magnetic bottle and synthesis of antihydrogen atoms in a cusp trap, where a spin-polarized antihydrogen beam can be extracted as an intensified beam. The magnetic bottle consists of an octupole coil and a pair of mirror coils, which improved the magnetic field uniformity near the axis, and so the stability of trapping antiprotons and positrons. Eventually, antihydrogen atoms were trapped for more than 1000s, which is ready to be testified with high precision laser spectroscopy. The cusp trap consists of a superconducting anti-Helmholtz coil and a stack of multiple ring electrodes. This success opens a new path to make a stringent test of the CPT symmetry via high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atoms.
Antihydrogen, a positron bound to an antiproton, is the simplest anti-atom. Its structure and properties are expected to mirror those of the hydrogen atom. Prospects for precision comparisons of the two, as tests of fundamental symmetries, are driving a vibrant programme of research. In this regard, a limiting factor in most experiments is the availability of large numbers of cold ground state antihydrogen atoms. Here, we describe how an improved synthesis process results in a maximum rate of 10.5 ± 0.6 atoms trapped and detected per cycle, corresponding to more than an order of magnitude improvement over previous work. Additionally, we demonstrate how detailed control of electron, positron and antiproton plasmas enables repeated formation and trapping of antihydrogen atoms, with the simultaneous retention of atoms produced in previous cycles. We report a record of 54 detected annihilation events from a single release of the trapped anti-atoms accumulated from five consecutive cycles.Antihydrogen studies are important in testing the fundamental principles of physics but producing antihydrogen in large amounts is challenging. Here the authors demonstrate an efficient and high-precision method for trapping and stacking antihydrogen by using controlled plasma.
Since 2002, experiments at CERN have been producing slow, but untrapped, antihydrogen. The ultimate goal of these experiments is to test CPT and the gravitational interactions of matter and antimatter. Most schemes to perform CPT and gravity tests require trapped antihydrogen, but trapping antihydrogen is much more difficult than merely synthesizing it. The principle problems that must be solved before we can trap are how to cool the antiprotons, and how to keep them cold during the synthesis process. While we have already learned how to cool antiprotons by ten orders of magnitude, we must cool them by four more orders of magnitude, a scale set by the relative size of the potentials of the antimatter plasmas from which the antiatoms are synthesized compared to the antihydrogen trap well depth. In this talk, I will discuss antihydrogen synthesis and some of the techniques we are developing to control the energy of the resultant antihydrogen.
Antihydrogen, the opposite number of hydrogen, is the simplest antimatter, and stable in vacuum, which guarantees a long observation time for high precision spectroscopy. This review discusses a short history of antimatter followed by the motivation of the cold antihydrogen research, and then a couple of latest results, which open a new era of antihydrogen research enabling high precision spectroscopy for the first time. A comparison of the spectroscopic properties of antihydrogen with those of hydrogen constitutes a stringent test of the CPT symmetry, the most fundamental law of physics. One of the important achievements of cold antihydrogen study in the last couple of years is the trapping of antihydrogen atoms in an octupole magnetic bottle. Considering the bottle depth, the trapped antihydrogen atoms were really cold, less than 0.5K in their temperature. High precision laser spectroscopy of 1S-2S transition is foreseen once antihydrogen atoms can be laser-cooled. The other milestone development was a successful synthesis of antihydrogen atoms in a so-called cusp trap, where an anti-Helmholtz coil configuration is adopted. The cusp trap enables extraction of antihydrogen atoms in a field-free region as an intensified spin-polarized beam,which realizes high resolution microwave spectroscopy of ground state hyperfine transitions.