Annual Review of Nuclear and Particle Science - Volume 54, 2004

A career devoted to the study of weak interactions and fundamental symmetries is summarized. Subjects include the induced pseudoscalar coupling in muon capture, the hypothesis of a superweak interaction, the oscillation of neutrinos in matter, and a parameterization of the CKM matrix of particular importance for B physics. Also discussed are the origin of the Aspen Center for Physics and activities related to the dangers of nuclear weapons.

The hep process is a weak-interaction reaction, ³He + p → ⁴He + e⁺ + νe, which occurs in the sun. There is renewed interest in hep owing to current experimental efforts to extract from the observed solar neutrino spectrum information on nonstandard physics in the neutrino sector. hep produces highest-energy solar neutrinos, although their flux is quite modest. This implies that the hep neutrinos can at some level influence the solar neutrino spectrum near its upper end. Therefore, a precise interpretation of the observed solar neutrino spectrum requires an accurate estimate of the hep rate. This is an interesting but challenging task. We describe the difficulties involved and how the recent theoretical developments in nuclear physics have enabled us to largely overcome these difficulties. A historical survey of hep calculations is followed by an overview of the latest developments. We compare the results obtained in the conventional nuclear physics approach and those obtained in a newly developed effective field theory approach. We also discuss the current status of the experiments relevant to hep.

Trace analysis of radionuclides is an essential and versatile tool in modern science and technology. Because of their ideal geophysical and geochemical properties, long-lived noble gas radionuclides—particularly ³⁹Ar (t1/2 = 269 y), ⁸¹Kr (t1/2 = 2.3 × 10⁵ y), and ⁸⁵Kr (t1/2 = 10.8 y)—have long been recognized to have a wide range of important applications in Earth sciences. In recent years, significant progress in the development of practical analytical methods has led to applications of these isotopes in the hydrosphere (tracing the flow of groundwater and ocean water). In this article, we introduce the applications of these isotopes and review three leading analytical methods: low-level counting (LLC), accelerator mass spectrometry (AMS) and atom trap trace analysis (ATTA).

The Gerasimov-Drell-Hearn sum rule is one of several dispersive sum rules that connect the Compton scattering amplitudes to the inclusive photoproduction cross sections of the target under investigation. Being based on such universal principles as causality, unitarity, and gauge invariance, these sum rules provide a unique testing ground to study the internal degrees of freedom that hold the system together. The present article reviews these sum rules for the spin-dependent cross sections of the nucleon by presenting an overview of recent experiments and theoretical approaches. The generalization from real to virtual photons provides a microscope of variable resolution: At small virtuality of the photon, the data sample information about the long-range phenomena, which are described by effective degrees of freedom (Goldstone bosons and collective resonances), whereas the primary degrees of freedom (quarks and gluons) become visible at the larger virtualities. Through a rich body of new data and several theoretical developments, a unified picture of virtual Compton scattering emerges, which ranges from coherent to incoherent processes, and from the generalized spin polarizabilities on the low-energy side to higher twist effects in deep-inelastic lepton scattering.

This article reviews the standard-model prediction for the anomalous magnetic moment of the muon and describes recent updates of QED, electroweak, and hadronic contributions. Comparison of theory and experiment suggests a 2.4 σ difference if e⁺e⁻→ hadrons data are used to evaluate the main hadronic effects, but a smaller discrepancy if hadronic τ decay data are employed. Implications of a deviation for “new physics” contributions, along with an outlook for future improvements in theory and experiment, are briefly discussed.

The E821 Experiment at the Brookhaven Alternating Gradient Synchrotron has measured the muon anomalous magnetic moment aμ to a relative precision of 0.5 parts per million. This effort required a new beamline, a super-ferric muon storage ring with a highly uniform magnetic field, a precision magnetic field measurement system, and electromagnetic calorimeters to record the electrons from muon decay, which carry the essential spin precession frequency information. Data obtained over five years resulted in more than nine billion analyzed events, in nearly equal samples of both muon charges. The experimental results aμ⁺ = 11 659 203(8) × 10⁻¹⁰ and aμ⁻ = 11 659 214(9) × 10⁻¹⁰ are consistent with each other, as predicted by the CPT invariance theorem. The combined result aμ ± = 11 659 208(6) × 10⁻¹⁰ is 0.9–2.4 standard deviations higher than predicted by theory; the range depends on the method employed to obtain the hadronic vacuum polarization term in the standard-model calculation. We review the experimental design, physical realization, and analysis procedures and compare the results to the theoretical prediction.

One can extract unique information about the nuclear interaction from the study of the heaviest elements. They exist solely on the basis of quantum effects, which create a barrier against spontaneous fission. The important questions concern the end of the periodic table and the location of the next closed nucleon shells. Considerable progress was achieved during the past few years in structure studies in this region. This was made possible by the development of detector systems for decay and in-beam studies using recoil separators and heavy ion fusion reactions. We concentrate on these developments and on recent results from structure studies in the region from einsteinium to dubnium. We present recent data on the elements 110 (darmstadtium), 111, and 112, and discuss claims for the synthesis of even heavier elements. We discuss the implications of these studies for predicting the location of the next spherical shells and give a brief outlook on the future.

We review the experimental and theoretical status of elastic electron scattering and elastic low-energy photon scattering (with both real and virtual photons) from the nucleon. As a consequence of new experimental facilities and new theoretical insights, these subjects are advancing with unprecedented precision. These reactions provide many important insights into the spatial distributions and correlations of quarks in the nucleon.

We discuss the physics motivations for building a 500 GeV–1 TeV electron-positron linear collider. The state-of-the-art collider technologies and the physics-driven machine parameters are discussed. Some of the phenomena well suited to study at a linear collider are described, including Higgs bosons, supersymmetry, other extensions to the standard model, and cosmology.

This article reviews the astrophysics and cosmological evidence for nonbaryonic dark matter (DM). It covers historical, current, and future experiments that look for direct evidence of particle DM. In addition, it surveys the underlying particle theories that provide some guidance about expected event rates, and the future prospects for the discovery of DM. A number of recent theoretical papers, making calculations in SUSY-based frameworks, show a spread of many (>5) orders of magnitude in the possible interaction rates for models consistent with existing cosmological and accelerator bounds. Within this decade, it seems likely that DM searches will be successful, or at the very least rule out a broad class of the currently most favored DM models.

We summarize residual background sources encountered in experiments conducted deep underground. Physical mechanisms of production and methods of estimation for the dominant sources are considered, and comparisons of the calculations with underground measurements are discussed. Principal background sources discussed include primary interactions of cosmic rays, mechanisms of neutron production by cosmic rays and low energy backgrounds from neutrons, primordial and anthropogenic radionuclides, and secondary radioactivity from spallation.

This review explains why generalized parton distributions and the related quantum phase-space distributions are useful in exploring the quark and gluon structure of the proton and neutron. It starts with the physics of form factors and parton distributions. Then quantum phase-space distributions and their offspring are discussed. The properties of generalized parton distributions are described. In particular, I elucidate the relation to the spin structure of the nucleon. Finally, various methods to determine the new distributions are explained.

Lattice quantum chromodynamics provides first-principles calculations for hadrons containing heavy quarks—charm and bottom quarks. Their mass spectra, decay rates, and some hadronic matrix elements can be calculated on the lattice in a model-independent manner. In this review, we introduce the effective theories that treat heavy quarks on the lattice. We summarize results on the heavy quarkonium spectrum, which verify the validity of the effective theory approach. We then discuss applications to B physics, which is the main target of the lattice theory of heavy quarks. We review progress in lattice calculations of the B meson decay constant, the B parameter, semileptonic decay form factors, and other important quantities.

Quantum chromodynamics (QCD), which describes hadrons and their interactions, is a non-Abelian gauge theory. The salient property of QCD is color confinement, quantitative understanding of which still remains a challenge. Major contributions to understanding quantum dynamics of non-Abelian fields are due to V.N. Gribov, both in the framework of pure gluodynamics (Gribov copies, Gribov horizon) and in the quest for confinement in the presence of light quarks (supercritical confinement scenario). We discuss Gribov's approach to the confinement problem and review some recent developments that are motivated, directly or indirectly, by his ideas.

The existence of gravitational radiation is a direct prediction of Einstein's theory of general relativity, published in 1916. The observation of gravitational radiation will open a new astronomical window on the universe, allowing the study of dynamic strong-field gravity, as well as many other astrophysical objects and processes impossible to observe with electromagnetic radiation. The relative weakness of the gravitational force makes detection extremely challenging; nevertheless, sustained advances in detection technology have made the observation of gravitational radiation probable in the near future. In this article, we review the theoretical and experimental status of this emerging field.