5 research outputs found
Physics with antihydrogen
Performing measurements of the properties of antihydrogen, the bound state of an antiproton and a positron, and comparing the results with those for ordinary hydrogen, has long been seen as a route to test some of the fundamental principles of physics. There has been much experimental progress in this direction in recent years, and antihydrogen is now routinely created and trapped and a range of exciting measurements probing the foundations of modern physics are planned or underway. In this contribution we review the techniques developed to facilitate the capture and manipulation of positrons and antiprotons, along with procedures to bring them together to create antihydrogen. Once formed, the antihydrogen has been detected by its destruction via annihilation or field ionization, and aspects of the methodologies involved are summarized. Magnetic minimum neutral atom traps have been employed to allow some of the antihydrogen created to be held for considerable periods. We describe such devices, and their implementation, along with the cusp magnetic trap used to produce the first evidence for a low-energy beam of antihydrogen. The experiments performed to date on antihydrogen are discussed, including the first observation of a resonant quantum transition and the analyses that have yielded a limit on the electrical neutrality of the anti-atom and placed crude bounds on its gravitational behaviour. Our review concludes with an outlook, including the new ELENA extension to the antiproton decelerator facility at CERN, together with summaries of how we envisage the major threads of antihydrogen physics will progress in the coming years
One-Particle Measurement of the Antiproton Magnetic Moment
\DeclareRobustCommand{\pbar}{\HepAntiParticle{p}{}{}\xspace}
\DeclareRobustCommand{\p}{\HepParticle{p}{}{}\xspace}
\DeclareRobustCommand{\mup}{{}{}\xspace}
\DeclareRobustCommand{\mupbar}{\mu_{\pbar}{}{}\xspace}
\DeclareRobustCommand{\muN}{{}{}\xspace
For the first time a single trapped \pbar is used to measure the \pbar
magnetic moment {\bm\mu}_{\pbar}. The moment {\bm\mu}_{\pbar} = \mu_{\pbar}
{\bm S}/(\hbar/2) is given in terms of its spin and the nuclear
magneton (\muN) by \mu_{\pbar}/\mu_N = -2.792\,845 \pm 0.000\,012. The 4.4
parts per million (ppm) uncertainty is 680 times smaller than previously
realized. Comparing to the proton moment measured using the same method and
trap electrodes gives \mu_{\pbar}/\mu_p = -1.000\,000 \pm 0.000\,005 to 5
ppm, for a proton moment ,
consistent with the prediction of the CPT theorem.Comment: 4 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1201.303
Cold neutral atoms via charge exchange from excited state positronium: a proposal
We present a method for generating cold neutral atoms via charge exchange
reactions between trapped ions and Rydberg positronium. The high charge
exchange reaction cross section leads to efficient neutralisation of the ions
and since the positronium-ion mass ratio is small, the neutrals do not gain
appreciable kinetic energy in the process. When the original ions are cold the
reaction produces neutrals that can be trapped or further manipulated with
electromagnetic fields. Because a wide range of species can be targeted we
envisage that our scheme may enable experiments at low temperature that have
been hitherto intractable due to a lack of cooling methods. We present an
estimate for achievable temperatures, neutral number and density in an
experiment where the neutrals are formed at a milli-Kelvin temperature from
either directly or sympathetically cooled ions confined on an ion chip. The
neutrals may then be confined by their magnetic moment in a co-located magnetic
minimum well also formed on the chip. We discuss general experimental
requirements
Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange
Lasers are used to control the production of highly excited positronium atoms (Ps*). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps* have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps* is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps* with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is expected to be increased by a similar factor