Any uncooled antiprotons are subsequently ejected by reducing the depth of the potential well. For this purpose we use a large (radius ~9 mm) plasma comprising ~8.5 × 10 7 electrons, which reduces the kinetic energy of about 73% of the antiprotons to below 100 eV in 20 s (this efficiency is not a fundamental limitation 15 it is merely a practical compromise adopted to realise the demonstrations reported here, without excessive fine-tuning of electron plasma and sequence timing parameters). Once captured they are sympathetically cooled by a batch of pre-loaded electrons which self-cool by the emission of cyclotron radiation in the cryogenic (~6 K) environment of the trap. Antiprotons from the CERN antiproton decelerator 13 (AD) are captured 14 in a high voltage (4 kV) Penning–Malmberg trap that we refer to as the catching trap (CT, not shown). It has been designed to allow the overlap of laser light and microwaves with trapped antihydrogen a schematic view of the device is shown in Fig. The central apparatus in which antihydrogen is formed is called ALPHA-2. The ALPHA apparatus comprises three systems that allow antiproton capture, positron accumulation and antihydrogen synthesis. Improved methods to produce cold antihydrogen are critically important to most experimental initiatives in the field, and hence the results presented here are of broad relevance see refs. These advances are realised through the development of a number of techniques that yield both more and colder antihydrogen. Here we report a breakthrough in the efficiency of antihydrogen trapping and a method for accumulating or stacking anti-atoms trapped during consecutive production cycles. Event topology is used to distinguish antiproton annihilations from cosmic rays. We employ a three-layer silicon vertex detector 11 to image the annihilation vertex position of each detected atom. Trapped antihydrogen is detected by ramping down the currents in the magnetic trap over 1.5 s and detecting the annihilation of the antiproton when the released atoms hit the wall of the trap. This is typically <0.5 K in temperature units for Tesla-scale trapping fields (multiplication by the Boltzmann constant k B to obtain energy units is implicit). Antihydrogen atoms in states where the magnetic moment is anti-aligned with the magnetic field are then confined in a magnetic minimum trap, provided their kinetic energy is low enough 1– 3. Ultimately, precision studies of antihydrogen properties complement, and are complemented by, experiments that probe the foundations of the standard model including studies of antiprotons 6, antiprotonic Helium 7, muonic atoms 8 and positronium, the electron-positron-bound state 9.Īntihydrogen is synthesised from antiprotons ( p ¯) and positrons (e +) the most widely employed method starts with cold plasmas of both species, which are brought together in Penning–Malmberg traps, where axial magnetic fields provide radial confinement and electric fields provide axial confinement (see ref. Significant work will be needed to achieve the levels of measurement precision obtained in the study of matter atoms. While the results of measurements conducted to date are consistent with the charge-parity-time invariance theorem, the field is still very much in its infancy. Here the authors demonstrate an efficient and high-precision method for trapping and stacking antihydrogen by using controlled plasma.Įnormous progress in antihydrogen ( H ¯) synthesis and trapping has been made in recent years 1– 3 and transitions between internal states have been induced and observed 4, 5. 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. 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. 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. In this regard, a limiting factor in most experiments is the availability of large numbers of cold ground state antihydrogen atoms. Prospects for precision comparisons of the two, as tests of fundamental symmetries, are driving a vibrant programme of research. Its structure and properties are expected to mirror those of the hydrogen atom. Antihydrogen, a positron bound to an antiproton, is the simplest anti-atom.
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