Low Energy Antiproton Experiments -- A Review

Low energy antiprotons offer excellent opportunities to study properties of fundamental forces and symmetries in nature. Experiments with them can contribute substantially to deepen our fundamental knowledge in atomic, nuclear and particle physics. Searches for new interactions can be carried out by studying discrete symmetries. Known interactions can be tested precisely and fundamental constants can be extracted from accurate measurements on free antiprotons ($\bar{p}$'s) and bound two- and three-body systems such as antihydrogen ($\bar{{\rm H}}=\bar{p}e^-$), the antprotonic helium ion (He$^{++} \bar{p}$)$^+$ and the antiprotonic atomcule (He$^{++} \bar{p}e^-$) . The trapping of a single $\bar{p}$ in a Penning trap, the formation and precise studies of antiprotonic helium ions and atoms and recently the production of $\bar{{\rm H}}$ have been among the pioneering experiments. They have led already to precise values for $\bar{p}$ parameters, accurate tests of bound two- and three-body Quantum Electrodynamics (QED), tests of the CPT theorem and a better understanding of atom formation from their constituents. Future experiments promise more precise tests of the standard theory and have a robust potential to discover new physics.Comment: invited talk, Workshop on Physics with Ultraslow Antiproton Beams, Riken Wako, Japan, 14-16 March 200

Past, Present and Future of Muonium

Muonium, the atom which consists of a positive muon and an electron, has been discovered by a team led by Vernon W. Hughes in 1960. It is in many respects the most ideal atom available from nature. Due to the close confinement in the bound state muonium can be used as an ideal probe of electro-weak interaction, including particularly Quantum Electrodynamics, and to search for additional yet unknown interactions acting on leptons. Recently completed experiments cover the ground state hyperfine structure, the 1s-2s interval and a search for spontaneous conversion of muonium to antimuonium. The experiments yield precise values for the fine structure constant, the muon mass and its magnetic moment. The results from these precision measurements have provided restrictions for a number of theories beyond the Standard Model of particle physics. Future precision experiments will require new and intense sources of muons.Comment: Proceedings of the Memorial Symposium in honor of Vernon Willard Hughes, Yale, 200

Free Muons and Muonium - Some Achievements and Possibilities in Low Energy Muon Physics

Some recent precision experiments in low energy muon physics are discussed. Spectroscopy on the muonium atom, the bound state of a positve muon and an electron, has provided precise tests of standard theory and yielded most precise values of important fundamental constants. A search for spontaneous muonium to antimuonium conversion test lepton flavour conservation and yields most stringent limits on parameters in several speculative models. The muon magnetic anomaly may contain hints to new physics and is a relevant calibration point for numerous models beyond standard theory. Since most precision experiments are limited by the particle fluxes at present muon sources, possibilities in this field are shown which will emerge at upgraded present facilities or new accelerator complexes under construction or planning. At such places novel techniques would be enabled

Searches for Permanent Electric Dipole Moments - Some Recent Developments

Searches for permanent electric dipole moments (EDMs) of fundamental particles render the possibility to discover New Physics beyond present Standard Theory. New ideas for experiments have come up recently which may allow to lower present limits substantially or even find unambiguous effects. Such are predicted by a variety of speculative models. The identification of potential sources for CP and T-violation will require to study several systems, which all have different sensitivity to possible mechanisms generating EDMs.Comment: 16th International Spin Physics Symposium, Trieste, 200

Lepton Flavour Violation Experiments -- Some Recent Developments

Dedicated experiments searching for lepton flavour violation can be performed very sensitively using K-decays and $\mu$-decays as well as neutrinoless double $\beta$-decay and muonium to antimuonium conversion. Although there is no confirmed signal reported yet, stringent limits for parameters in speculative extensions to the standard model can be set. Some models could recently be ruled out.Comment: submitted to Proceedings of 1st Tropical Workshop in Particle Phyics and Cosmolog

Some Aspects of Fundamental Symmetries and Interactions

The known fundamental symmetries and interactions are well described by the Standard Model. Features of this powerful theory, which are described but not deeper explained, are addressed in a variety of speculative models. Experimental tests of the predictions in such approaches can be either through direct observations at the highest possible accelerator energies or through precision measurements in which small deviations from calculated values within the Standard Model are searched for. Antiproton physics renders a number of possibilities to search for new physics.Comment: Invited talk, International Conference on Low Energy Antiproton Physics 05, Bonn, Germany, May 16-22, 200

A discrete martingale model of pension fund guarantees in

In this paper we present a solution to the problem of pricing guarantees of minimum returns on pension fund contributions. These guarantees exist by law in Colombia and cover all pension fund contributions made to the country's private pension fund administration companies (AFPs). As of September 1997, the funds were collecting contributions of 2.5 million affiliates with an accumulated capital of 1.8 billion dollars starting from zero in 1994. Two types of guarantees exist: on obligatory contributions and on voluntary contributions. The solutions are based on a discrete martingale approach . We show that both guarantees are equivalent to an ''option to exchange.'' However, in the case of voluntary contributions a ceiling on the payoff s must be added. Using a discrete martingale framework and a binomial solution we develop all aspects of the model that are necessary for its practical application in the context of the pension fund guarantees. Binomial formulas are obtained for both forms of guarantees. Besides solving the problem of pricing the guarantees offered by insurance fund, the contributions in terms of options theory of this paper are: i) we adapt the binomila model of options to exchange to relate the relevant parameters of the same to a continuous-time lognormal process; ii) we provide a binomial solution to the problem of an option to exchange with a ceiling. We then investigate the incentives that the current fixed-price system introduces and propose possible systems of incentives that can be used to encourage higher-risk investment by the AFP's and a shift of the fund's portfolio to risky equity and debt. Given the country's effort to encourage capital markets development and the financing of the real sector via private financial markets, this strategy appears to be desirable from the social and economic point of view.Pension funds, guarantees, options pricing, Colombia, Latin America

Diffusion Tensor Imaging: on the assessment of data quality - a preliminary bootstrap analysis

In the field of nuclear magnetic resonance imaging, diffusion tensor imaging (DTI) has proven an important method for the characterisation of ultrastructural tissue properties. Yet various technical and biological sources of signal uncertainty may prolong into variables derived from diffusion weighted images and thus compromise data validity and reliability. To gain an objective quality rating of real raw data we aimed at implementing the previously described bootstrap methodology (Efron, 1979) and investigating its sensitivity to a selection of extraneous influencing factors. We applied the bootstrap method on real DTI data volumes of six volunteers which were varied by different acquisition conditions, smoothing and artificial noising. In addition a clinical sample group of 46 Multiple Sclerosis patients and 24 healthy controls were investigated. The response variables (RV) extracted from the histogram of the confidence intervals of fractional anisotropy were mean width, peak position and height. The addition of noising showed a significant effect when exceeding about 130% of the original background noise. The application of an edge-preserving smoothing algorithm resulted in an inverse alteration of the RV. Subject motion was also clearly depicted whereas its prevention by use of a vacuum device only resulted in a marginal improvement. We also observed a marked gender-specific effect in a sample of 24 healthy control subjects the causes of which remained unclear. In contrary to this the mere effect of a different signal intensity distribution due to illness (MS) did not alter the response variables