Annual Review of Nuclear and Particle Science - Volume 53, 2003

The author traces his involvement in the evolution of particle accelerators over the past 50 years. He participated in building the first billion-volt accelerator, the Brookhaven Cosmotron, which led to the introduction of the “strong-focusing” method that has in turn led to the very large accelerators and colliders of the present day. The problems of acceleration of spin-polarized protons are also addressed, with discussions of depolarizing resonances and “Siberian snakes” as a technique for mitigating these resonances.

We review the status of hyperon semileptonic decays. The central issue is the Vus element of the CKM matrix, for which we obtain Vus = 0.2250 (27). This value is similar in precision to the one derived from Kl3, but higher, and in better agreement with the unitarity requirement, |Vud|² + |us|² + |Vub|² = 1. We find that the Cabibbo model gives an excellent fit to baryon–beta-decay form-factor data (χ² = 2.96 for 3 degrees of freedom) with F + D = 1.2670 ± 0.0030, F − D = −0.341 ± 0.016, and no indication of flavor-SU(3)–breaking effects. We indicate the need for more experimental and theoretical work, both on hyperon beta decays and on Kl3 decays.

We review recent experimental tests of the gravitational inverse-square law and the wide variety of theoretical considerations that suggest the law may break down in experimentally accessible regions.

We discuss the neutral-kaon system and demonstrate the advantage of strangeness tagging as performed by the CPLEAR experiment. The main results of CPLEAR on tests of discrete symmetries are reviewed.

We review lattice QCD investigations at high temperature. After a short introduction to thermal QCD on the lattice, we report on the present understanding of the phase diagram and the equation of state, particularly in the presence of dynamical quarks. We discuss various screening lengths in the plasma phase, including results from dimensionally reduced QCD. We then summarize lattice data on quark-number susceptibilities and spectral densities, both of which are immediately relevant to the interpretation of heavy-ion experiments. A major section is devoted to simulations of QCD at small, yet phenomenologically important, values for the baryon density.

The τ neutrino was the last standard-model fermion to be directly observed. We report on the strategy, design, and results of the DONuT experiment. The data were acquired at Fermilab during 1997, and in July 2000, the DONuT collaboration presented four τ-neutrino interactions. Modern nuclear-emulsion processing was the key technology that made it possible to detect the decay of τ leptons produced in charged-current interactions of τ neutrinos. The precision of the emulsion data and the speed of digitization enabled the use of novel methods to locate interaction vertices and search for decays in emulsion data. We also discuss the level of background in the τ signal, which is small enough to permit the identification of individual τ events with high confidence.

The identification of direct-reaction processes and their subsequent exploitation for the spectroscopy of weak radioactive beams of exotic nuclei are important problems in modern nuclear physics. One- and two-nucleon knockout reactions, studied using intermediate-energy radioactive beams, have been shown to be powerful tools for this purpose. This article discusses the current status of such investigations and reviews what has been learned to date from the experiments and analyses of the past five years. The techniques are still in their formative stages, and the open questions and challenges are outlined.

For over 20 years, charge-coupled devices (CCDs) have dominated most digital imaging applications and markets. Today, complementary metal oxide semiconductor (CMOS) arrays are displacing CCDs in some applications, and this trend is expected to continue. Low cost, low power, on-chip system integration, and high-speed operation are unique features that have generated interest in CMOS arrays. This paper reviews current CCD and CMOS sensor developments and related applications. We compare fundamental performance parameters common to these technologies and describe why the CCD is considered a mature technology, whereas CMOS arrays have significant room for growth. The paper presents custom CMOS pixel designs and related fabrication processes that address performance deficiencies of the CCD in high-performance applications. We discuss areas of development for future CCD and CMOS imagers. The paper also briefly reviews hybrid imaging arrays that combine the advantages of CCD and CMOS, producing better sensors than either technology alone can provide.

We survey top-quark physics from what has been learned so far at the Tevatron to the searches planned at present and future colliders. We summarize the richness of the measurements and discuss their possible impact on our understanding of the standard model by pointing out their key elements and limitations. We discuss how the top quark may provide a connection to new or unexpected physics. The literature on many of the topics we address is sizeable. We attempt to consolidate the most salient points into a complete, coherent overview.

Until recently, CP violation had been observed only in kaon decays. In order to conclusively interpret CP violation and test whether it can be explained in the framework of the Cabibbo-Kobayashi-Maskawa matrix, two asymmetric B factories, KEK-B and PEP-II, were constructed in the past decade. Recent measurements with the two detectors at these B factories clearly established large CP violation in neutral B mesons. We review the results and outline the prospects for future measurements.

We review the current status of flavor-changing neutral currents in the charm sector. We focus on the standard-model predictions and identify the main sources of theoretical uncertainties in both mixing and rare charm decays. The potential of these observables for constraining short-distance physics in the standard model and its extensions is compromised by the presence of large nonperturbative effects. We examine the possible discovery windows in which short-distance physics can be tested and study the effects of various extensions to the standard model. The current experimental situation and future prospects are reviewed.