Positronium cooling in porous silica measured via Doppler spectroscopy

In recent years, there has been a wealth of new science involving low-energy antimatter (i.e., positrons and antiprotons) at energies ranging from 10 2 to less than 10 −3 eV. Much of this progress has been driven by the development of new plasma-based techniques to accumulate, manipulate and deliver antiparticles for specific applications. This article focuses on the advances made in this area using positrons. However many of the resulting techniques are relevant to antiprotons as well. An overview is presented of relevant theory of single-component plasmas in electromagnetic traps. Methods are described to produce intense sources of positrons and to efficiently slow the typically energetic particles thus produced. Techniques are described to trap positrons efficiently and to cool and compress the resulting positron gases and plasmas. Finally, the procedures developed to deliver tailored pulses and beams (e.g., in intense, short bursts, or as quasi-monoenergetic continuous beams) for specific applications are reviewed. The status of development in specific application areas is also reviewed. One example is the formation of antihydrogen atoms for fundamental physics [e.g., tests of invariance under charge conjugation, parity inversion and time reversal (the CPT theorem), and studies of the interaction of gravity with antimatter]. Other applications discussed include atomic and materials physics studies and study of the electron-positron many-body system, including both classical electron-positron plasmas and the complementary quantum system in the form of Bose-condensed gases of positronium atoms. Areas of future promise are also discussed. The review concludes with a brief summary and a list of outstanding challenges.

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“…This technique is expected to play a key role in efforts to create a positronium-atom BEC (Sec. VIII.C.1.c) (Cassidy et al, 2010a).…”

Section: Spin Polarized Positronsmentioning

confidence: 96%

Plasma and trap-based techniques for science with positrons

Danielson¹,

Dubin²,

Greaves³

et al. 2015

Rev. Mod. Phys.

231

222

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“…The lifetime of a fraction of o-Ps is shortened in the nanoporosities by pick-off annihilation, in which the positron of the o-Ps annihilates with an electron of the walls of the pores into 2 c-rays. Porous silica has proved to be a good choice for converting positrons into cold positronium due to the large Ps yield in the bulk and on the porous surface, combined with the relatively efficient cooling of o-Ps by collisions with the walls of the pores [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Characterization of a transmission positron/positronium converter for antihydrogen production

Aghion

Amsler

Ariga

et al. 2017

Nuclear Instruments and Methods in Physics Research Section B:

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and 10 ns temporal width. The forward emission of implanted positrons and secondary electrons was investigated with a micro-channel plate -phosphor screen assembly, connected either to a CCD camera for imaging of the impinging particles, or to a fast photomultiplier tube to extract information about their time of flight. The maximum Ps formation fraction was estimated to be $10%. At least 10% of the positrons implanted with an energy of 3.3 keV are forward-emitted with a scattering angle smaller than 50°and maximum kinetic energy of 1.2 keV. At least 0.1-0.2 secondary electrons per implanted positron were also found to be forward-emitted with a kinetic energy of a few eV. The possible application of this kind of positron/positronium converter for antihydrogen production is discussed.

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“…The positrons are accelerated to 2.5 keV and implanted into a porous silica (SiO 2 ) film [16] in a magnetic field of 13 mT. Ps atoms are produced with an efficiency of ∼30% and a mean kinetic energy of ∼50 meV [17]. Following emission from the SiO 2 target the Ps atoms form a rapidly expanding dilute gas with an initial density of ∼10 7 cm −3 .…”

mentioning

confidence: 99%

“…These atoms were excited via single-photon 1 3 S 1 → 2 3 P 0;1;2 transitions, driven using pulsed (∼6 ns FWHM) ultraviolet laser radiation with a wavelength of ≃243.01 nm. A laser with a large bandwidth (85 GHz) was employed in order to address a significant fraction of the Doppler broadened (> 500 GHz) transition linewidth [17]. Peak laser intensities of ≤ 0.…”

mentioning

confidence: 99%

Controlling Positronium Annihilation with Electric Fields

et al. 2015

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We show that the annihilation dynamics of excited positronium (Ps) atoms can be controlled using parallel electric and magnetic fields. To achieve this, Ps atoms were optically excited to n ¼ 2 sublevels in fields that were adjusted to control the amount of short-lived and long-lived character of the resulting mixed states. Inclusion of the former offers a practical approach to detection via annihilation radiation, whereas the increased lifetimes due to the latter can be exploited to optimize resonance-enhanced two-photon excitation processes (e.g., 1 3 S → 2 3 P → nS=nD), either by minimizing losses through intermediate state decay, or by making it possible to separate the excitation laser pulses in time. In addition, photoexcitation of mixed states with a 2 3 S 1 component represents an efficient route to producing long-lived pure 2 3 S 1 atoms via single-photon excitation. DOI: 10.1103/PhysRevLett.115.183401 PACS numbers: 36.10.Dr, 78.70.Bj Positronium (Ps) is an atomic system composed of an electron bound to a positron and has several unique properties, the most striking of which are its low mass (M Ps ¼ 2m e ) and the fact that it can decay through various annihilation pathways [1]. Electron-positron annihilation requires overlap of the particle wave functions [2] and in Ps is therefore dependent on the square of the radial wave function at the origin. This is zero for states with l > 0 [3]. Higher order annihilation processes can occur for states with l > 0 but are strongly suppressed [4] and in practice direct Ps annihilation occurs only from the ground 1 1 S 0 and 1 3 S 1 , and metastable 2 1 S 0 and 2 3 S 1 levels. The inhibition of Ps annihilation in states with l > 0 is the basis for several proposed schemes to manipulate annihilation rates using resonant and nonresonant laser fields [5][6][7][8][9][10][11]. More complex strategies have also been suggested [12,13], although these have also not yet been experimentally demonstrated.The radiative decay and annihilation time scales in the n ¼ 2 manifold in Ps span an enormous range: The 2 1 S 0 level is radiatively metastable, fluorescing on a time scale of ≃0.24 s [3], but annihilating in 1 ns; conversely the 2 3 P 0;1;2 levels decay by fluorescence to the 1 3 S 1 state in 3.19 ns, but their annihilation lifetimes exceed 100 μs [4]. The 2 3 S 1 level is also metastable and fluoresces in ≃0.24 s, but has an annihilation lifetime of ∼1.14 μs [1]. It is the disparate properties of these states that make the approach described here to manipulating decay rates particularly effective.We report the results of experiments in which Ps annihilation rates in a weak magnetic field are manipulated using parallel electric fields. This combination of fields permits control over the spin multiplicity and orbital angular momentum character of the n ¼ 2 sublevels accessible by single-photon excitation from the 1 3 S 1 ground state. By increasing the 2 1 P character of mixed states in the fields, radiative decay to the short-lived singlet ground state (1 1 S 0 ) can be...

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Positronium cooling in porous silica measured via Doppler spectroscopy

Cited by 127 publications

References 77 publications

Plasma and trap-based techniques for science with positrons

Plasma and trap-based techniques for science with positrons

Characterization of a transmission positron/positronium converter for antihydrogen production

Controlling Positronium Annihilation with Electric Fields

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