Antihydrogen synthesis: A progress report

The main suggested routes for atomic antihydrogen ( ) formation will be reviewed in a pedestrian fashion. These are the following reactions: , and (iii) . The present status of the projects related to these reactions, as well as the projects' experimental scope, will also be discussed or referred to. Some speculations will be made regarding the physics that can be yielded by an antihydrogen probe.     

Behaviour and spectroscopy of (anti) hydrogen atoms in strong magnetic fields

Since it has been demonstrated that antiprotons can be captured in sizeable amounts in ion traps, the intriguing question has been raised whether or not these antiprotons can be used for producingantihydrogen atoms. One route proposed is the merging of trapped antiprotons with a cold trapped plasma of positrons. In this case the formation of antihydrogen proceeds most likely through three-body recombination (p⁻e⁺e⁺→ e⁺) into high Rydberg states of , followed by a rapid cascade of transitions to low-lying states. To assess the influence of the trapping magnetic field (on the order of a few tesla) upon the formation process of we review the present knowledge of the behaviour and properties of hydrogen (and antihydrogen) atoms in strong magnetic fields — a subject which has been very topical in recent years because of its relation to the problem of “quantum” chaos.     

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.     

Antiproton low-energy collisions with Ps-atoms and true muonium atoms (μ + μ −)

Three-charge-particle collisions with participation of ultra-slow antiprotons ( \(\overline {\rm {p}}\) ) is the subject of this work. Specifically we compute the total cross sections and corresponding thermal rates of the following three-body reactions: \(\overline {\rm p}+(e^+e^-) \rightarrow \overline {\rm {H}} + e^-\) and \(\overline {\rm p}+(\mu ^+\mu ^-) \rightarrow \overline {\rm {H}}_{\mu } + \mu ^-\) , where \(e^-(\mu ^-)\) is an electron (muon) and \(e^+(\mu ^+)\) is a positron (antimuon) respectively, \(\overline {\rm {H}}=(\overline {\rm p}e^+)\) is an antihydrogen atom and \(\overline {\rm {H}}_{\mu }=(\overline {\rm p}\mu ^+)\) is a muonic antihydrogen atom, i.e. a bound state of \(\overline {\rm {p}}\) and μ ⁺. A set of two-coupled few-body Faddeev-Hahn-type (FH-type) equations is numerically solved in the framework of a modified close-coupling expansion approach.     

Signals of left-right supersymmetry ine + e − collisions

We study chargino and neutralino pair production at the Next Linear e⁺ e⁻ Collider in a supersymmetric left-right model. We investigateon- and off-resonance signals via the processes: and . These reactions could lead to observable signals as they compare with the background signal from W^± -pair production.     

Antihydrogen (hydrogen) atom formation

In this paper we show how the ATHENA data samples on the antihydrogen ( ${\bar{\rm H}}$ ) formation in very different conditions provide useful information on the two different possible mechanisms: the 3-body reaction ( $\bar{p}+{e^+}+{e^+}\rightarrow {\bar{\rm H}}+ e^+$ ) and the 2-body reaction ( $\bar{p}+{\rm e^+}\rightarrow {\bar{\rm H}}+{h\nu}$ ).     

Theoretical cross sections for keV antiprotons

Partial and total close-coupled semiclassical (impact parameter) cross sections and total classical Monte-Carlo cross sections for interactions in and , p+H collisions are computed in the intermediate keV range for antiprotons, , up to 100 keV lab. Total cross sections for antihydrogen, , formation are found to be large, 10−20×10⁻¹⁶ cm² in a wider energy range than was anticipated earlier, up to some 20 keV lab. New estimates of cross sections for ionisation of atomic hydrogen by antiproton impact are reported for the low-energy range 1–30 keV lab where they are 10−20×10⁻¹⁷ cm², being much larger than the corresponding cross sections for ionisation of hydrogen by proton impact. Data for excitation of H by impact is also presented.     

The neutrinos in muon decay

We review the available information on the identity of the neutrino states emitted in muon decay, and discuss the exotic decay .     

Higher-order QED corrections to e^ + e^ - \to v\bar v\gamma at LEP2

The process with a distinctive “photon-plus-missing-energy” signal can serve as an important tool to search for new physics at LEP2. It can be exploited to measure the WWγ coupling, or to search for weakly interacting and invisible (s)particles. For meaningful comparisons of experimental data with theoretical predictions, higher-order QED corrections due to multiphoton emission must be taken into account. In the present paper we explain how the WWγ coupling has been incorporated into the KORALZ Monte Carlo program, which can now be used for simulations of events with higher-order QED corrections. The strategy of how to perform an experimental analysis in the presence of experimental cuts is proposed. The question of systematic uncertainties is addressed and some numerical results for the phenomenologically interesting case of anomalous WWγ couplings are also given.     

Antihydrogen formation by autoresonant excitation of antiproton plasmas

In efforts to trap antihydrogen, a key problem is the vast disparity between the neutral trap energy scale ( $\sim\!50\,\upmu\mathrm{eV}$ ), and the energy scales associated with plasma confinement and space charge (~1 eV). In order to merge charged particle species for direct recombination, the larger energy scale must be overcome in a manner that minimizes the initial antihydrogen kinetic energy. This issue motivated the development of a novel injection technique utilizing the inherent nonlinear nature of particle oscillations in our traps. We demonstrated controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm or tenuous plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination. The nature of this injection overcomes some of the difficulties associated with matching the energies of the charged species used to produce antihydrogen.     

Designing an RFQ ring trap for antiproton confinement and trapping and laser cooling Mg+ ions

Summary In the true sense of Bernie's approach to physics, an old idea (the Radiofrequency Quadrupole Trap) was taken and upgraded to be applied to a new area of physics (formation of an antihydrogen beam). During the course of the development work, new applications were identified and immediately put to use. While the collaboration is still pursuing its original goal, formation of antihydrogen by Bernie's reaction, collisions between positronium atoms and antiprotons, many new experiments have been found possible and are actively pursued. These include atomic and nuclear physics studies with ultra-low energy antiprotons ejected from the initial catching trap of the antihydrogen project, and the formation and study of exotic atoms and molecules in ultra-thin targets using trapped antiprotons (an extension of the work by the PS205 collaboration at CERN described elsewhere in this volume [10]). A large physics community has grown around these ideas and may even succeed in obtaining its very own antiproton source, which is a true sign of the recognition of the importance of this field. The work in this area will hopefully continue for many years to come, but we will truly miss the motivation and drive of our friend and colleague, Bernie Deutch.     

Radiative production of the lightest neutralino in e + e − annihilation

The production of the lightest stable neutralino in the process including general mixing of gauginos and Higgsinos is studied. General formulas for the differential cross section are presented. The dependence of the differential cross section on the photon energy spectrum and also the dependence of the total cross section on the beam energies for three different mixing scenarios are illustrated. The text was submitted by the author in English.     

Perturbative QCD coherence ine + e − annihilation

We study the pattern of soft parton radiation in the hard annihilation processes \(e^ + e^ - \to q\bar q\gamma \) and \(e^ + e^ - \to q\bar qg\) by explicit evaluation of the cross sections for \(e^ + e^ - \to q\bar q\gamma g\) and \(e^ + e^ - \to q\bar qgg + q\bar qq\bar q\) taken care of correct normalization. We find the coherence effects as observed experimentally and discuss why these effects are not present in the usual models based onO(α _s ² ) perturbation theory with subsequent independent fragmentation.     

Exclusive production of charmed-meson pairs

It is shown that data of the BELLE Collaboration on the exclusive production of charmedmeson pairs via the one-photon mechanism of e⁺e^? annihilation can be adequately described within the constituent quark model. It is also shown that the cross section for the central production of two D mesons in the process \(e^ + e^ - \to e^ + e^ - \gamma \gamma \to e^ + e^ - D\bar D + X\) is commensurate with the cross section for their production in one-photon annihilation.     

Gaugino-Higgsino mixing in selectron and sneutrino pair production

We study \(e^ + e^ - \to \tilde e^ + \tilde e^ - \) together with \(\tilde e^ \pm \) decay emphasizing the importance of neutralino mixing in thet-channel at energies above theZ ⁰ resonance. This illustrated in three different mixing scenarios. Formulae for \(e^ + e^ - \to \bar \tilde v_e \tilde v_e \) are also given.     

On the question of supersymmetric particles production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

Some aspects of supersymmetric particles pair production in e ⁺ e ^?-annihilation in processes \(e^ + + e^ - \to \tilde l^ + + \tilde l^ -\), \(e^ + + e^ - \to \tilde \chi ^ + + \tilde \chi ^ -\) are studied. Aparatus, in which long-lived charged particles deceleraition and accumulation take place, is considered. Binding energy of a negatively charged particle with nucleus is obtained. Probability of β-decay of a nucleus bounded with a long-lived negatively charged particle is considered.     

Radioactive Production of the Lightest Neutralino in the Process of <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation

The production of the lightest stable neutralino in the reaction with general mixing of the higgsino and gaugino is studied. General formulas for differential cross sections are presented. The dependence of the effective differential cross section on the photon energy spectrum and electron mass is illustrated together with the dependence of the effective total cross section on the beam energy for three different scenarios. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–57, June, 2005.     

Low energy antiprotons in the cosmic rays: A new upper limit

Kinematics predicts the severe suppression of low-energy (<1 GeV) secondary antiprotons in the Galactic cosmic rays. Thus the observation several years ago of a finite flux of low-energy antiprotons could not be explained with existing models of cosmic ray propagation, which led to a plethora of theoretical speculation. We have recently flown a balloon-borne instrument to measure the energy spectrum of cosmic-ray , and have found no antiprotons in the energy interval 200–640 MeV (corrected to the top of the atmosphere). This yields an upper limit to the ratio of 5.5×10⁻⁵ (90% confidence level), well below and hence contradicting the earlier result.     

Investigation of the <Emphasis Type="Italic">Hττ</Emphasis> and <Emphasis Type="Italic">Hbb</Emphasis> coupling constants for a scalar (pseudoscalar) Higgs boson at a future linear electron-positron collider

The possibility of setting constraints on the couplings of a scalar (pseudoscalar) Higgs boson to the tau lepton and the b quark in the reactions \(e^ + e^ - \to \nu \bar \nu \tau ^ + \tau ^ - \) and \(e^ + e^ - \to \nu \bar \nu b\bar b\) at a future linear electron-positron collider of total energy \(\sqrt s = 500 GeV\) is studied. The admixture of a new hypothetical pseudoscalar state of the Higgs boson in the H ff vertex is parametrized in the form (m _f /ν)(a+iγ₅b). On the basis of an analysis of differential distributions for the processes under study, it is shown that data from the future linear collider TESLA will make it possible to constrain the parameters a and b as ?0.32≤Δa≤0.24 and ?0.73≤b≤0.73 in the case of the reaction \(e^ + e^ - \to \nu \bar \nu \tau ^ + \tau ^ - \) and as ?0.026≤Δa≤0.027 and ?0.23≤b≤0.23 in the case of the reaction \(e^ + e^ - \to \nu \bar \nu b\bar b\). It is emphasized that the contribution of the fusion subprocess WW → H in the channel involving an electron neutrino is of particular importance, since this contribution enhances the sensitivity of data to the parameters being analyzed.     

A single trapped antiproton and antiprotons for antihydrogen production

During the last several years, our TRAP collaboration has pioneered techniques for slowing, trapping, cooling and indefinitely storing antiprotons to energies more than 10¹⁰ times lower than previously possible. The radio signal from a single trapped antiproton is now being used for precision measurements. Many cold antiprotons are stacked as another important step toward the eventual production of antihydrogen, and positrons have been trapped in vacuum.