Annual Review of Nuclear and Particle Science - Volume 64, 2014

The author describes in some technical detail his career in experimental particle physics. It began in 1955, when he joined Brookhaven National Laboratory, and ended in 1985, when he moved to the field of cosmic-ray physics. The author discusses not only his successes but also his failures and his bad judgments. This period was the golden age of particle physics, when the experimental possibilities were abundant and one could carry out experiments with a small team of colleagues and students.

Electromagnetic polarizabilities describe the response of a system to the application of an external quasi-static electric or magnetic field. In this article, we examine experimental and theoretical work addressing the polarizabilities of the light hadrons.

We review the effective field theory approach to physics beyond the Standard Model using dimension-six operators. Topics include the choice of operator basis, electroweak boson pair production, precision electroweak physics (including one-loop contributions), and Higgs physics. By measuring the coefficients of dimension-six operators with good accuracy, we can hope to infer some or all of the features of the theory that lies beyond the Standard Model.

IceCube is the first kilometer-scale neutrino detector. Built primarily for neutrino astronomy, it has recently discovered events with energies above 100 TeV that are likely to be from distant sources beyond the solar system. Among the events are three with deposited energies of more than 1 PeV, the highest-energy neutrinos ever detected. We review the astrophysical arguments that motivate such a large detector, and we describe how it works and how the high-energy events are reconstructed and identified above the background of atmospheric neutrinos. We also describe the broad range of neutrino physics and particle astrophysics topics addressed by IceCube, as well as its potential for the future.

We review the modern view of fluid dynamics as an effective low-energy, long-wavelength theory of many-body systems at finite temperature. We introduce the concept of a nearly perfect fluid, defined by a ratio η/s of shear viscosity to entropy density of order ℏ/kB or less. Nearly perfect fluids exhibit hydrodynamic behavior at all distances down to the microscopic length scale of the fluid. We summarize arguments that suggest that there is fundamental limit to fluidity, and we review the current experimental situation of measurements of η/s in strongly coupled quantum fluids.

We review the status of the coupling constants of chiral Lagrangians in the meson sector, the so-called low-energy constants (LECs). We emphasize the chiral SU(2) and SU(3) Lagrangians for the strong interactions of light mesons and discuss the theoretical and experimental input for determining the corresponding LECs. In the two-flavor sector, we review the knowledge of the LECs from both continuum fits and lattice QCD analyses. For chiral SU(3), next-to-next-to-leading-order (NNLO) effects play a much greater role. Our main new results are fits of the LECs Li at both next-to-leading order (NLO) and NNLO, making extensive use of the available knowledge of NNLO LECs. We compare our results with available lattice determinations. We then discuss resonance saturation of LECs and the convergence of chiral SU(3) to NNLO. Finally, we review the status of predictions for the LECs of chiral Lagrangians with dynamical photons and leptons.

Superconducting cavities have been operating routinely in a variety of accelerators with a range of demanding applications. With the success of completed projects, niobium cavities have become an enabling technology, offering upgrade paths for existing facilities and pushing frontier accelerators for nuclear physics, high-energy physics, materials science, and the life sciences. With continued progress in basic understanding of radio-frequency superconductivity, the performance of cavities has steadily improved to approach theoretical capabilities.

This review discusses the status of string physics where the string tension is around the TeV scale. It covers model-building basics for perturbative strings, based on D-brane configurations. The effective low-energy physics description of such string constructions is analyzed: how anomaly cancellation is implemented, how fast proton decay is avoided, and how D-brane models lead to additional Z′ particles. This review also discusses direct search bounds for strings at the TeV scale, as well as theoretical issues with model building related to flavor physics and axions.

Both charm and bottom quarks form nonrelativistic bound states analogous to positronium. The J/ψ and ψ(2S) charmonium states and the first three Ψ(nS) bottomonium states, all spin-triplet S-wave quarkonium states below open heavy-flavor thresholds, have relatively large branching ratios to e⁻e⁺ or μ⁻μ⁺ pairs. In hadron collisions, experiments measuring lepton pairs can determine polarization by using angular correlation techniques. The polarization, in turn, can be related theoretically to the production mechanism for the bound state. This review summarizes experimental studies with proton beams at fixed-target and colliding-beam accelerators, covering a center-of-mass energy range from 39 to 7,000 GeV for nucleon and antiproton targets. Analyses using various polarization frames and spin-quantization axes are described and results compared. A pattern emerges that connects experimental results over the whole energy span. The theoretical implications of the pattern are presented, and a set of new measurements is proposed.

The possibility of double-beta (ββ) decay was recognized in the mid 1930s, and by 1939 something of its potential to reveal fundamental properties of the neutrino was known as well. But experimental observation of the phenomenon was out of reach. Despite numerous attempts over the next 30 years, and strong suggestions of its existence from geochemical experiments, ββ decay had not been observed to occur in the laboratory. Our group at UC Irvine took up the search in the early 1970s, first with a cloud chamber and then with a time-projection chamber. The following narrative traces a discovery process that unfolded over the ensuing 15 years—a sequence of setbacks and false starts punctuated by occasional victories and, ultimately, by a definitive laboratory observation of two-neutrino ββ decay, in August 1987.

Scattering polarized electrons provides an important probe of the weak interactions. Precisely measuring the parity-violating left–right cross-section asymmetry (ALR) is the goal of a number of experiments that have recently been completed or are in progress. The experiments are challenging, given that ALR is small, typically between 10⁻⁴ and 10⁻⁸. By carefully choosing appropriate targets and kinematics, one can isolate various pieces of the weak Lagrangian, providing a search for physics beyond the Standard Model. For other choices, unique features of the strong interaction are being studied, including the radius of the neutron density in heavy nuclei, charge symmetry violation, and higher-twist terms. This article reviews the theory behind the experiments, as well as the general techniques used in the experimental program.

In this article, I discuss existing and planned techniques for cooling high-energy hadron beams, provide practical formulae for estimating cooling rates, and address difficulties and challenges.

The LHC has collided protons on protons at center-of-mass energies of 7 and 8 TeV between 2010 and 2012, referred to as the Run I period. We review the current status of searches for new physics beyond the Standard Model at the end of Run I by the ATLAS and CMS experiments, limited to the 8-TeV search results that have been published or submitted for publication as of the end of February 2014. We discuss some of the implications of these searches on the existence of TeV-scale new physics, with a special focus on two open questions: the hierarchy problem and the nature of dark matter. Finally, we give an outlook for the future.

Atmospheric neutrinos are produced by cosmic-ray interactions in the atmosphere. Atmospheric neutrino experiments typically observe zenith-angle and energy dependences of and νe events. Through these experiments, neutrino oscillation was discovered. Since then, various studies have been performed to further our understanding of neutrino properties. This article discusses experimental studies of neutrino oscillations with atmospheric neutrinos.

The top quark is the heaviest known elementary particle, and it is often considered a window through which to search for new physics processes in particle physics. A large program to study the top quark properties has been carried out at both the Tevatron and LHC colliders by the D0, CDF, ATLAS, and CMS experiments. The most recent results are discussed in this review.

We present the first LHC results on hard-probe observables in heavy-ion collisions. During the first 3 years of operation, the ALICE, ATLAS, and CMS experiments each collected Pb + Pb interaction data, corresponding to an integrated luminosity above 100 μb⁻¹ at TeV. Fresh insights into the properties of QCD matter under extreme conditions are emerging. Although the basic picture established at RHIC—that of a hot, dense medium that (a) flows with a viscosity-to-entropy ratio close to the conjectured lower bound and (b) quenches the energy of hard probes, such as jets, heavy flavor, and quarkonia—has been confirmed at the LHC, the higher-energy data indicate new ways to extract its properties in more detail. These include the first observations of a different strength for the suppression of charm and beauty quarks, reduced low-pT suppression for J/ψ, and detailed measurements of high-ET jet suppression and jet-fragmentation modifications.