Towards laser spectroscopy of antihydrogen

The development of the first continuous coherent source at 121.56 nm is described. Radiation at this wavelength of Lyman α can be used for laser cooling of antihydrogen on the strong 1S–2P transition. It also opens up a possibility for precision spectroscopy that requires just a few antihydrogen atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Laser spectroscopy of hydrogen and antihydrogen

Recent advances in high resolution laser spectroscopy of atomic hydrogen are reviewed. Two-photon spectroscopy of the 1S–2S transition in a cold atomic beam has reached a resolution of better than 1 part in 10¹¹. This narrow resonance has already led to order-of-magnitude advances in precision measurements of the Rydberg constant, the 1S ground state Lamb shift, and the hydrogen deuterium isotope shift. A precise spectroscopic comparison of hydrogen and antihydrogen could provide stringent tests of basic symmetry laws. Possible scenarios for ultrahigh resolution laser spectroscopy of antihydrogen are discussed.     

Towards antihydrogen trapping and spectroscopy at ALPHA

Spectroscopy of antihydrogen has the potential to yield high-precision tests of the CPT theorem and shed light on the matter-antimatter imbalance in the Universe. The ALPHA antihydrogen trap at CERN??s Antiproton Decelerator aims to prepare a sample of antihydrogen atoms confined in an octupole-based Ioffe trap and to measure the frequency of several atomic transitions. We describe our techniques to directly measure the antiproton temperature and a new technique to cool them to below 10 K. We also show how our unique position-sensitive annihilation detector provides us with a highly sensitive method of identifying antiproton annihilations and effectively rejecting the cosmic-ray background.     

Resonance spectroscopy of gravitational states of antihydrogen

We study a method to induce resonant transitions between antihydrogen ( \(\bar {H}\) ) quantum states above a material surface in the gravitational field of the Earth. The method consists in applying a gradient of magnetic field which is temporally oscillating with the frequency equal to a frequency of a transition between gravitational states of antihydrogen. Corresponding resonant change in a spatial density of antihydrogen atoms can be measured as a function of the frequency of applied field. We estimate an accuracy of measuring antihydrogen gravitational states spacing and show how a value of the gravitational mass of the \(\bar {H}\) atom can be deduced from such a measurement.     

Measurement of the hyperfine structure of antihydrogen in a beam

A measurement of the hyperfine structure of antihydrogen promises one of the best tests of CPT symmetry. We describe an experiment planned at the Antiproton Decelerator of CERN to measure this quantity in a beam of slow antihydrogen atoms.     

Precision spectroscopy of metastable hydrogen and antihydrogen with a Lamb-shift polarimeter

A spinfilter, the most important component of a Lamb-shift polarimeter, can be used to produce a beam of metastable hydrogen (deuterium) atoms in one hyperfine state (α1, α2 and together with the Sona transition β3). As function of a magnetic field separated transitions between the 2S _1/2 metastable hyperfine states seem to be observable as well as single transitions into the short-lived 2P _1/2 and 2P _3/2 states. The Breit-Rabi diagrams for these states can be measured with good precision. Furthermore, the hyperfine splittings and the Lamb shift can be observed as well. Application of this method to anti-hydrogen atoms are suggested.     

Trapped antihydrogen for spectroscopy and gravitation studies: Is it possible?

Possibilities for trapping and cooling antihydrogen atoms for spectroscopy and gravitational measurements are discussed. A measurement of the gravitational force on antihydrogen seems feasible if antihydrogen can be cooled to of order 1 milli-Kelvin. Difficulties in obtaining this low energy are discussed in the hope of stimulating required experimental and theoretical studies.     

Towards antihydrogen confinement with the ALPHA antihydrogen trap

ALPHA is an international project that has recently begun experimentation at CERN’s Antiproton Decelerator (AD) facility. The primary goal of ALPHA is stable trapping of cold antihydrogen atoms with the ultimate goal of precise spectroscopic comparisons with hydrogen. We discuss the status of the ALPHA project and the prospects for antihydrogen trapping.     

Towards the production of an ultra cold antihydrogen beam with the AEGIS apparatus

The AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) experiment is an international collaboration, based at CERN, with the experimental goal of performing the first direct measurement of the Earth’s gravitational acceleration on antihydrogen. In the first phase of the experiment, a gravity measurement with 1% precision will be performed by passing a beam of ultra cold antihydrogen atoms through a classical Moiré deflectometer coupled to a position sensitive detector. The key requirements for this measurement are the production of ultra cold (T～100?mK) Rydberg state antihydrogen and the subsequent Stark acceleration of these atoms. The aim is to produce Rydberg state antihydrogen by means of the charge exchange reaction between ultra cold antiprotons (T～100?mK) and Rydberg state positronium. This paper will present details of the developments necessary for the successful production of the ultra cold antihydrogen beam, with emphasis on the detector that is required for the development of these techniques. Issues covered will include the detection of antihydrogen production and temperature, as well as detection of the effects of Stark acceleration.     

Fast ion beam collinear laser spectroscopy: Some aspects of recent applications,sensitivity and resolution

This contribution deals with some selected aspects of Fast Ion Beam Collinear Laser Spectroscopy: (1) the study of h.f.i. in free ions; (2) sensitive state selective particle detection; (3) laser-RF double resonance; and (4) laser frequency Doppler tuning in external magnetic fields.     

Beyond antihydrogen: testing CPT with the molecular antihydrogen ion

Measurements of Zeeman, Zeeman-hyperfine and ro-vibrational transitions in \(\bar {H}_{2}^{-}(\bar {p}e^{+}\bar {p})\) compared to \(H_{2}^{+}\) have the potential for more precise tests of CPT than can be obtained from antiprotons and antihydrogen. In particular, measurements of ro-vibrational transitions have a potential sensitivity to a difference between antiproton and proton mass three orders of magnitude higher than antihydrogen/hydrogen. Methods are outlined for precision measurements on a single \(\bar {H}_{2}^{-}\) or \({H}_{2}^{+}\) ion in a cryogenic Penning trap, with non-destructive state identification using the continuous Stern-Gerlach effect or changes in mass. \(\bar {H}_{2}^{-}\) can be produced using the \(\bar {H}^{+}+\bar {p} \rightarrow \bar {H}_{2}^{-} + e^{+}\) reaction.     

Relativistic antihydrogen production

Antihydrogen has recently been produced in collisions of antiprotons with ions. While passing through the Coulomb field of a nucleus an antiproton will create an electron-positron pair. In rare cases the positron is bound by the antiproton and an antihydrogen atom produced. We calculate the production of relativistic antihydrogen atoms by bound-free pair production. The cross section is calculated in the semiclassical approximation (SCA), or equivalently in the plane wave Born approximation (PWBA) using exact Dirac-Coulomb wave functions. We compare our calculations to the equivalent photon approximation (EPA). Received: 19 December 1997 / Published online: 10 March 1998     

Cold antihydrogen atoms

Cold antihydrogen atoms have been produced recently by mixing trapped antiprotons with cold positrons. The efficiency is remarkable: more than 10% of the antiprotons form antihydrogen. Future spectroscopy of antihydrogen has the potential to provide new extremely precise tests of the fundamental symmetry between matter and antimatter. In addition, cold antihydrogen atoms might permit the first direct experiments investigating antimatter gravity. A novel method to measure the gravitational acceleration of antimatter using ultra-cold antihydrogen atoms is proposed. PACS 04.80.Cc; 32.80.Pj; 36.10.-k     

Fast beam collinear laser-rf double resonance

The method and application of fast beam collinear laser-rf double resonance are discussed. Following a short theoretical treatment of the collinear interaction of fast atoms with rf and laser fields, the experimental procedure and some technical details are presented. Selected applications of the method: (i) hyperfine structure and atomicg-factor measurements, and (ii) experimental studies of fundamental aspects of atom-field interactions, are described. prospective applications in nuclear physics experiments are discussed.     

Collinear laser ion beam spectroscopy

Collinear Laser Ion Beam Spectroscopy (CLIBS) investigates hyperfine structures (hfs) and isotope shifts (IS) in spectral lines and is well suited for the study of nuclear moments of short-lived isotopes. It is fast, highly selective, highly sensitive and allows many experimental alternatives. The high accuracy makes it also an interesting tool for atomic physics. A basic experimental setup is described. Results for nuclear moments and radii in Sm, Eu, Gd show that the accuracy of hfs and IS data is much better than the resulting moments. We discuss the hfs-anomaly and its dependence on atomic quantum numbers (L, S, J) and show that its determination is possible without the knowledge of the nuclear magnetic moments. A hfs-anomaly in respect of the nuclear quadrupole moment was not found. IS-measurements are used to determine permanent and fluctuating nuclear deformation. The standard interpretation is inconsistent in the case of Eu. Modifications of the theory are suggested. Crossed second order (CSO) effects affect the IS values. We show that CSO-effects may help to determine the field effect of the IS experimentally.     

Trapped positrons for antihydrogen

Positrons from a 12 mCi²²Na source are slowed by a W(110) reflection moderator and then captured in a Penning trap, by damping their motion with a tuned circuit. Because of the stability of the Penning trap and the cryogenic ultra-high vacuum environment, we anticipate that positrons can be accumulated and stored indefinitely. A continuous loading rate of 0.14 e⁺/s is observed for 32 h in this initial demonstration. More than 1.6×10⁴ positrons have thus been trapped and stored at 4 K, with improvements expected. The extremely high vacuum is required for compatibility with an existing antiproton trap, which has already held more than 10⁵ antiprotons at 4 K, for producing antihydrogen at low temperatures. The extremely cold positrons in high vacuum may also prove to be useful for cooling highly stripped ions.     

Spectroscopy with relativistic antihydrogen

A technique is described for measuring the Lamb shift in antihydrogen in Fermilab experiment E862. The sensitivity of the measurement is expected to be 4.5%. This revised version was published online in August 2006 with corrections to the Cover Date.     

CPT-symmetry studies with antihydrogen

Various approaches to physics beyond the Standard Model can lead to small violations of CPT invariance. Since CPT symmetry can be measured with ultra-high precision, CPT tests offer an interesting phenomenological avenue to search for underlying physics. We discuss this reasoning in more detail, comment on the connection between CPT and Lorentz invariance, and review how CPT breaking would affect the (anti)hydrogen spectrum.