Positron trapping in an electrostatic well by inelastic collisions with nitrogen molecules

Murphy, T. J.; Surko, C. M.

doi:10.1103/physreva.46.5696

Cited by 219 publications

(190 citation statements)

References 17 publications

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“…Unlike their matter counterparts, antihydrogen atoms must be synthesized 18 by merging cold plasmas of antiprotons and positrons in specially configured Penning-Malmberg traps. In the ALPHA-2 device, we typically mix 90,000 antiprotons, slowed and captured from the Antiproton Decelerator, with 1.6 million positrons from a Surko-type accumulator 19 to produce about 25,000 antihydrogen atoms. These numbers are monitored in daily baseline measurements that involve ejecting particles onto a multichannel plate detector.…”

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confidence: 99%

Observation of the hyperfine spectrum of antihydrogen

Ahmadi

Alves

Baker

et al. 2017

Nature

109

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The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers 1-3 and the measurement 4 of the zero-field groundstate splitting at the level of seven parts in 10 13 are important achievements of mid-twentieth-century physics. The work that led to these achievements also provided the first evidence for the anomalous magnetic moment of the electron 5-8 , inspired Schwinger's relativistic theory of quantum electrodynamics 9,10 and gave rise to the hydrogen maser 11 , which is a critical component of modern navigation, geo-positioning and very-long-baseline interferometry systems. Research at the Antiproton Decelerator at CERN by the ALPHA collaboration extends these enquiries into the antimatter sector. Recently, tools have been developed that enable studies of the hyperfine structure of antihydrogen 12 -the antimatter counterpart of hydrogen. The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms 13,14 provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter 12,15 . Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies. The data reveal clear and distinct signatures of two allowed transitions, from which we obtain a direct, magneticfield-independent measurement of the hyperfine splitting. From a set of trials involving 194 detected atoms, we determine a splitting of 1,420.4 ± 0.5 megahertz, consistent with expectations for atomic hydrogen at the level of four parts in 10 4 . This observation of the detailed behaviour of a quantum transition in an atom of antihydrogen exemplifies tests of fundamental symmetries such as charge-parity-time in antimatter, and the techniques developed here will enable more-precise such tests.In an earlier experiment 12 using the original ALPHA apparatus 16 , we demonstrated microwave-induced spin flips in trapped antihydrogen. The current work was carried out using the second-generation ALPHA-2 device (Fig.

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confidence: 99%

Observation of the hyperfine spectrum of antihydrogen

Ahmadi

Alves

Baker

et al. 2017

Nature

109

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“…1. Antihydrogen is synthesized by mixing plasmas of antiprotons from the antiproton decelerator (about 90,000 particles) and positrons from a Surko-type accumulator 14,15 (about 1.6 million particles). The techniques used in this experiment yield about 25,000 antihydrogen atoms per mixing attempt.…”

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confidence: 99%

Observation of the 1S–2S transition in trapped antihydrogen

Ahmadi

Alves

Baker

et al. 2016

Nature

129

140

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The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S-2S transition by Hänsch 1 to a precision of a few parts in 10 15 . Recent technological advances have allowed us to focus on antihydrogen-the antimatter equivalent of hydrogen 2-4 . The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today's Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S-2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10 −10 .

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“…A 1.274 MeV gamma ray, γ, follows shortly after (3.7 ps) as the excited Ne * nucleus undergoes an isomeric transition to the ground The ALPHA apparatus includes a dedicated Surko-type positron accumulator [115,116] (Fig. 3.7), a device which continuously collects, cools, and stores positrons emitted where they continue to cool via futher collisions with the buffer gas.…”

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confidence: 99%

Detection of Trapped Antihydrogen

Hydomako

2013

Springer Theses

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The ALPHA experiment is an international effort to produce, trap, and perform precision spectroscopic measurements on antihydrogen (the bound state of a positron and an antiproton). Based at the Antiproton Decelerator (AD) facility at CERN, the ALPHA experiment has recently magnetically confined antihydrogen atoms for the first time. A crucial element in the observation of trapped antihydrogen is ALPHA's silicon vertexing detector. This detector contains sixty silicon modules arranged in three concentric layers, and is able to determine the three-dimensional location of the annihilation of an antihydrogen atom by reconstructing the trajectories of the produced annihilation products.This dissertation focuses mainly on the methods used to reconstruct the annihilation location. Specifically, the software algorithms used to identify and extrapolate charged particle tracks are presented along with the routines used to estimate the annihilation location from the convergence of the identified tracks. It is shown that these methods can determine the annihilation location with a spatial resolution between about 0.6 to 0.8 cm (depending on the coordinate being measured). Furthermore, a robust analysis to identify and reduce cosmic ray background events is described. The cosmic ray background can obscure the trapped antihydrogen signal, and its suppression leads to a significant increase in the annihilation detection sensitivity. The background suppression analysis involves examining the reconstructed detector event based on several selection criteria, including: the number of charged particle tracks, the radial vertex position, and a fit of a straight line to the event hit positions. By carefully optimizing these criteria, (99.54 ± 0.02)% of cosmic ray events are rejected, while (64.4 ± 0.1)% of antihydrogen annihilation events are retained. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon i detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

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Positron trapping in an electrostatic well by inelastic collisions with nitrogen molecules

Cited by 219 publications

References 17 publications

Observation of the hyperfine spectrum of antihydrogen

Observation of the hyperfine spectrum of antihydrogen

Observation of the 1S–2S transition in trapped antihydrogen

Detection of Trapped Antihydrogen

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