Applications Of Quantum Chromodynamics Research Articles

Editorial: Biographical Memoirs , Volume 68

Editorial: <i>Biographical Memoirs</i> , Volume 68

William James Stirling CBE. 4 February 1953—9 November 2018

James Stirling's wide-ranging contributions to the development and application of quantum chromodynamics were central in verifying QCD as the correct theory of strong interactions, and in computing precise predictions for all types of collider processes. He published more than 300 papers on a vast range of phenomenological topics, including some of the most highly cited of all time in particle physics. His research, always full of insight, focused on the confrontation of theoretical predictions with experimental results. Amongst many key contributions, he developed the helicity amplitude method and used it to show that the CERN ‘monojet’ events, thought to be a possible signal of new physics, were due to vector boson plus jet production. The method has since facilitated the calculation of many other important processes. At Durham he formed a famous long-standing collaboration that set the standard for determining the quark and gluon distributions in the proton. Besides his intellectual brilliance, his personal qualities of humility, modesty, diligence and fairness made him an outstanding scientific leader and administrator. He played a major role in the foundation of the Institute for Particle Physics Phenomenology in Durham and served as its first Director. In 2005 he was appointed Pro-Vice Chancellor for Research at Durham. He moved to the Cavendish Laboratory in Cambridge in 2008, becoming Head of the Department of Physics in 2011. Then in 2013 he was appointed to the newly created position of Provost, the chief academic officer, at Imperial College, London, from which he retired in August 2018.

What is the structure and spin decomposition of the proton?

The structure of the is the forefront of studies on the deep structure of matter. With developments of high energy experiments in particular deeply inelastic lepton nucleon scattering (DIS), a dynamical picture of the structure of the has been developed, i.e., the quantum chromodynamics (QCD) based parton model. According to this picture, a moving close to the speed of light can be viewed as a bunch of free partons, and the collision between two high energy protons can be viewed as the collision between partons. Partons in the are described by parton distribution functions (PDFs). This picture is very successful in describing data from different experiments. It has been widely accepted in high energy physics community and is now taken as the standard picture for the dynamical structure of hadrons. The picture has changed the concepts of structures of matter in the sense that the number of partons in a depends on the space and time resolution of the probe. The studies of the structure provide not only the necessary initial condition of high energy collision but also the most active and fruitful frontier for studying properties of QCD where new QCD application techniques have been developed such as the collinear expansion and factorization theorem. With developments of experimental techniques, the studies have been extended to include spin degree of freedom and to use different probes such as electrons and muons. These studies have lead to many new discoveries, initiated the well known proton spin crisis and the proton radius puzzle, and attracted much more attention in the field of particle and nuclear physics. The experimental data from polarized DIS has revealed that quark spin contributes to only a small fraction of the spin and initiated the question where the spin comes from. The electromagnetic radius of the measured from the electron-proton interaction does not coincide with that measured from the muon-proton interaction and initiated the radius puzzle. The experimental data on single-spin asymmetries in inclusive hadron production in proton-proton collisions have lead the studies of the QCD parton model from the simplest one dimensional longitudinal distribution case to the three dimensional case including spin and transverse momentum dependences. The physics in the three-dimensional case is definitely much more abundant and interesting. The transverse momentum dependent (TMD) PDFs include the simple number densities, the helicity distributions, the transversity, and many spin-momentum correlation functions as well, such as the Sivers function, the Boer-Mulders function, the Collins function, worm-gear, pretzelosity and also many so-called higher twist distributions describing quantum interference effects. Both experimental and theoretical efforts have been made in last years and many progresses have been made. The planned new instrumentations such as the Electron-Ion Collider (EIC) in the United States will definitely bring the field to a new era of rapid developments. Several new equipment discussed in China, including Super-Z Factory, Circular Electron Positron Collider (CEPC) and EIC of China (EicC) at High Intensity heavy ion Accelerator Facility (HIAF) and so on can also bring very significant contributions even play dominant role in some of the aspects in this exciting field.

Resource Letter QCD-1: Quantum chromodynamics

This Resource Letter provides a guide to the literature on quantum chromodynamics (QCD), the relativistic quantum field theory of the strong interactions. Journal articles, books, and other documents are cited for the following topics: Quarks and color, the parton model, Yang–Mills theory, experimental evidence for color, QCD as a color gauge theory, asymptotic freedom, QCD for heavy hadrons, QCD on the lattice, the QCD vacuum, pictures of quark confinement, early and modern applications of perturbative QCD, the determination of the strong coupling and quark masses, QCD and the hadron spectrum, hadron decays, the quark-gluon plasma, the strong nuclear interaction, and QCD’s role in nuclear physics.

The Bottom-Up Implementation of One MILC Lattice QCD Application on the Cell Blade

We report the results of the bottom-up implementation of one MILC lattice quantum chromodynamics (QCD) application on the Cell Broadband Engine™ processor. In our implementation, we preserve MILC's framework for scaling the application to run on a large number of compute nodes and accelerate computationally intensive kernels on the Cell's synergistic processor elements. Speedups of 3.4× for the 8 × 8 × 16 × 16 lattice and 5.7× for the 16 × 16 × 16 × 16 lattice are obtained when comparing our implementation of the MILC application executed on a 3.2 GHz Cell processor to the standard MILC code executed on a quad-core 2.33 GHz Intel Xeon processor. We provide an empirical model to predict application performance for a given lattice size. We also show that performance of the compute-intensive part of the application on the Cell processor is limited by the bandwidth between main memory and the Cell's synergistic processor elements, whereas performance of the application's parallel execution framework is limited by the bandwidth between main memory and the Cell's power processor element.

THE BEHAVIOR OF THE GAUGE-BOSON PROPAGATOR IN THE DIFFERENT PHASES OF QED3

As a toy model of quantum chromodynamics (QCD), we investigate the influence of the vacuum polarization on the photon propagator, in massless quantum electrodynamics in 2+1 dimensions (QED3), using the coupled Dyson–Schwinger equations for the fermion and photon propagators with a range of fermion–photon vertices. It is found that the form of the photon propagators in the Nambu–Goldstone and Wigner phases exhibit distinctly different behaviors and it is expected that similar things happen in QCD. Hence in the phenomenological application of QCD one should choose different forms of gluon propagator as input to solve the quark self-energy functions in the two different phases, especially in the study of QCD phase transitions. In addition, employing these results, we discuss the causation of dynamical chiral symmetry breaking (DCSB) in QED3 and compare it with that in QCD.

THEORY OF WEAK INTERACTIONS: RECENT DEVELOPMENT AND PROBLEMS

Accumulation of theoretical experience, on one hand, and experimental data, on the other, resulted in a considerable progress in weak interactions. The current literature concentrates mainly on such issues as the study of the Kobayashi-Maskawa matrix and the application of quantum chromodynamics to concrete processes. Here I discuss the most interesting developing fields referring both to old (light) and new (heavy) hadrons. The first part is devoted to [Formula: see text] oscillations and other processes of the second order yielding information on Vbu and the t quark mass. The second and the largest part describes the modern QCD-based approaches in the traditional problems (K meson and hyperon physics) and in new problems associated with heavy quarks.

Applications of QCD to the Production of Mesons and Jets in Hadron-Hadron Collisions

Applications of the theory of quantum chromodynamics (QCD) with asymptotic freedom to processes involving large momentum transfers are examined. The theory describes correctly many features of the lepton initiated processes eN, μN, vN, vN as well as large-mass muon-pair production and the production of mesons and jets at large p⊥ in hadron-hadron collisons. Some predictions are made for future large p⊥ meson and jet experiments. The preliminary conclusion is that QCD might well be the correct theory behind all these phenomena, although a definitive test has not yet been made.

Charmonium and gluons

Afther the discovery of J/ψ and ψ′ mesons many other narrow resonances were found which represent various levels of a system called charmonium. In this review theoretical interpretation of charmonium properties is given. The classification of charmonium levels and their electromagnetic and strong decays are discussed. The basic assumption is that strong interaction between charmed quark and charmed antiquark in charmonium is mediated by coloured gluons as described by Quantum Chromodynamics (QCD). It is argued that charmonium is an ideal object to test the basic ideas of QCD. Both the traditional nonrelativistic approach to charmonium and the dispersion one are presented. The latter approach is free from many additional assumptions inherent to potential calculations. Other applications of QCD to the charmed world are briefly reviewed. Different parts of the review are addressed to different readers. It could, in particular, be of interest to students, specializing in elementary particle physics, experimentalists and theoreticians who are active in this field. The final results are presented in such a form as to follow for a direct comparison with corresponding experimental data.