High Energy and Particle Physics

High Energy and Particle Physics

High Energy and Particle Physicists study the most basic constituents of matter and antimatter and the forces that govern their interactions. They are responsible for developing the Standard Model that pinpoints leptons and quarks as the basis of all normal matter in the Universe and that identifies gauge bosons as carriers that mediate three of the four forces of nature. Enormous accelerators are used to create particles that normally do not occur in every-day life, but which existed in the earliest stages of the development of the Universe after the Big Bang. Much work remains to be done: dark matter and dark energy remain enigmas, the predominance of matter over antimatter can’t be explained, and gravity resists unification.

Here are the researchers in High Energy and Particle Physics who are able to supervise graduate students. To see a detailed profile of anyone, including contact information, click on the title bar or portrait. To see a personal research website (if available), click on the research picture.

Neutrinos, especially neutrino mixing; Antimatter; Charge-Parity (CP) violation; Particle and radiation detectors.

I study the properties of the neutrino, the least understood of the fundamental particles in our universe, but one that plays a key role in unsolved problems in particle physics and cosmology. Lately, I have been doing so as a member of the T2K experiment in Japan. The consequence of the breakthrough discovery that neutrinos have mass (by the experiments SuperK in Japan and SNO in Canada), contrary to the assumption in the Standard Model of particle physics, gives rise to quantum mechanical mixing among the 3 known neutrinos, encoded in matrix form. One of the goals of T2K was to determine the last unknown parameter in this matrix, theta_13, which is accessible by studying the transformation of muon neutrinos to electron neutrinos (so-called “neutrino oscillations”). At T2K, beams of neutrinos and anti-neutrinos are produced from protons hitting a graphite target. Precise monitoring of this proton beam is essential for understanding the neutrino flux, which is an input parameter for physics studies. I have worked on one of the monitoring devices, an Optical Transition Radiation (OTR) detector, which is critical for measuring the proton beam characteristics in the high radiation environment near the target. The most important outcome of our experiments so far is a measurement that theta_13 is non-zero and relatively large, for which the T2K team was awarded a prestigious prize by La Recherche, a French science magazine. Our results show a way forward to investigate whether neutrino physics holds the key to why our universe is made only of matter, despite matter and anti-matter being produced equally in the Big Bang. We plan to investigate the origin of the matter/antimatter asymmetry by comparing results from data collected with neutrino and anti-neutrino beams.

Experimental high-energy particle physics; Radio-frequency superconductivity in metallic films.

I am interested in collisions between the most elementary particles available, at the highest possible momentum transfer, and have been involved in the development of instrumentation to do observe them. One focus is the limiting behaviour of niobium and films of niobium and niobium alloys used in superconducting radio-frequency cavities, the aim being to increase the affordable energy of a future linear collider. Previously, I studied high momentum transfer elastic scattering and electron-positron annihilation (ARGUS at DESY). I also participated in the development and construction of the ZEUS calorimeter at DESY, which led to observations that challenged the Standard Model of particle physics.

Theoretical cosmology, especially cosmic inflation, eternal inflation, dark energy, and confrontations with observations; Field theory; String theory; Gravitation.

The goal of my research is to understand the fundamental laws of nature through their impact on cosmology. I am primarily a theorist, dabbling in cosmology, field theory, string theory, and gravitation. I am actively engaged in research on cosmic inflation, eternal inflation, topological defects, and models of dark energy. I also design data analysis algorithms to confront fundamental theory with observations of the Cosmic Microwave Background (CMB) radiation. Here is a sampling of the questions that drive my research: How big is the universe? What might lie beyond our observable universe, and how could we confirm or disprove various proposals? What role do the extra dimensions predicted by string theory play in cosmology? What is the fundamental nature of space-time singularities? Are there new ways of looking at cosmological datasets that could be useful when confronting theories with data? Can computer simulations of the very early universe shed light on its possible initial conditions and evolution?

Strongly-coupled quantum field theories, especially qantum chromodynamics; Lattice field theory simulations.

I aim to understand strongly coupled quantum field theories, quantum chromodynamics (QCD) in particular. QCD is the theory of the nuclear and sub-nuclear strong force, the force that binds protons and neutrons to form nuclei and at a deeper level, the force that binds quarks to form neutrons and protons. Although the theory can be stated very compactly and elegantly, its solution has eluded physicists for decades. This is perhaps not surprising as QCD can be thought of as a theory of 104 complex-valued quantum variables at each point in space. One of the most promising approaches for studying QCD is Monte-Carlo simulation of the field theory on a space-time lattice. I use this technique to study nuclear forces, colour-flux-tube breaking and other problems.

Quantum chromodynamics (QCD); Lattice quantum field theories; Physics beyond the Standard Model, including dark matter.

Inside the protons and neutrons of every atom's nucleus, there are quarks. The strong force that is responsible for the perpetual confinement of quarks is described by Quantum Chromodynamics (QCD). My recent research has combined theoretical methods with supercomputer simulations to explore this quantum theory of quarks via lattice QCD computations, chiral perturbation theory, and heavy quark symmetry. My work also extends to theories beyond the Standard Model of particle physics.

Quantum chromodynamics (QCD); Chiral perturbation theory.

I am interested in the consequences of the Standard Model of particle physics for few-body nuclear systems and low-energy particle physics and dynamics. My recent research has focussed on Quantum Chromodynamics (QCD), the theory of the strong interactions, using the techniques of chiral perturbation theory and various versions of QCD sum rules to study weak, strong, and electromagnetic observables.

Experimental tests of the Standard Model of particle physics; Matter/Antimatter asymmetry; Antihydrogen; Physics education.

I am an experimental high-energy particle physicist. Fundamentally, my research is aimed at testing the Standard Model of particle physics. The Standard Model is a fully predictive theory that describes all matter in terms of 12 elementary particles (quarks and leptons) plus the Higgs boson. It also explains interactions between particles as arising from the exchange of other particles. There are two parts to the Standard Model - Quantum Chromodynamics (QCD) which describes the strong/colour interactions between quarks, where gluons carrying the colour charge are exchanged, and the Electroweak Theory which describes electroweak interactions, such as beta decay and electron energy levels in atoms, where photons and the W and Z bosons are exchanged. The goal of experimental particle physics is to use sophisticated particle detectors and very high energy particle accelerators to learn even more about the interactions and properties of the fundamental particles so as to constrain or possibly even cause a complete re-evaluation of the Standard Model.

What particularly interests me is the observation that hardly anything in the Universe today is composed of antimatter, the so-called "Baryon Asymmetry". This is one of the biggest problems in science, because the Standard Model guides us to believe that the Big Bang produced normal matter and antimatter in equal proportions. Since matter and antimatter annihilate upon contact, the preponderance of normal matter today means that there had to be a slight excess of matter over antimatter in the early Universe. To set that up, there must exist an asymmetry somewhere in particle interaction rates. In other words, there must be one or more processes in which the rate in one direction (that of producing normal matter) is slightly higher than the rate in the opposite direction (that of producing antimatter). Thus, much of the work I have done and am doing now has been concerned with studying relationships between normal matter and antimatter.

Presently, I am collaborating on the Antihydrogen Laser Physics Apparatus (ALPHA) at CERN in Geneva, which has made a series of ground-breaking measurements of great significance. ALPHA was undertaken to shed light on the origin of the imbalance between matter and antimatter, the view being that detailed study of the antimatter version of hydrogen (the most prevalent atom in the Universe) might reveal an asymmetry in particle interactions at a deep level. My students and I have led the development of the particle detectors for tracking and locating antihydrogen. The ALPHA team managed to create and trap antihydrogen for the first time and measure its charge (the same as hydrogen, namely zero, within errors). We are in the process of determining whether antihydrogen falls or rises under the force of gravity, and at what rate. Our ultimate objective is to quantify with exquisite precision how well the energy levels of hydrogen and antihydrogen match.

Magnetic monopoles and Q-balls; Supersymmetry and Higgs bosons; Electronics for high-energy physics experiments.

I am an experimental high-energy particle physicist. I am particularly interested in searching for new particles predicted by some theories, such as magnetic monopoles and supersymmetric particles. I am also interested in the development of custom electronics for particle searches. I am a member of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, which is the world’s highest energy particle accelerator. As such, I contributed to the 2012 discovery of a new particle believed to be the Higgs boson.

Particle physics is the study of the smallest constituents of matter and the four fundamental forces between them. Our current understanding is that the world is made up of six quarks and six leptons, each apparently grouped into pairs, forming three similar families of matter. Research shows that quarks and leptons do not have any substructure, that is, that they are the fundamental particles. Each of these particles is partnered with an antiparticle with the same mass but the opposite charge. The standard theoretical model of particle physics does not explain why these particles appear in three families, nor does it predict the particle masses. At a cosmological level, we do not understand why the Universe appears to be dominated by matter as opposed to antimatter, nor do we understand the source of the “dark matter” that represents 23% of the matter in the universe. Perhaps there are particles we have yet to discover. To help answer these questions, we need to go back to the Big Bang, when the universe was minute and the temperatures and densities of matter were enormous. Particle accelerators are the tools we use to recreate the conditions of the universe shortly after the Big Bang.

Presently, the York ATLAS group is engaged in a search for magnetic monopoles. All magnetic objects that have ever been observed have a north pole at one end and a south pole at the other end. A magnetic monopole is a particle postulated to carry only a south or a north pole. If a magnetic monopole exists, theory shows that this would explain why there appears to be a fundamental unit of electric charge.  This is one of the outstanding mysteries in particle physics today!

We are also involved in searches for particles predicted by Supersymmetry, which is an attempt to unify the strong and weak forces in the Standard Model.  One of the particles predicted by Supersymmetry could be the source of dark matter. Whether or not Supersymmetry exists, ATLAS is certain to discover new physics. So far, we have focussed on searching for a counterpart of the Z boson predicted by a version of Supersymmetry called LeptoSUSY.

We also create custom electronics for particle detection with ATLAS. To that end, I established an electronics test and development laboratory that includes the state of the art equipment necessary for such leading edge electronics projects. For example, we have worked on readout electronics (including firmware development) for the Transition Radiation Tracker in the ATLAS inner detector. We are currently building electronics to select magnetic monopoles in real time at ATLAS.

Dark matter; Physics of the weak scale; Matter/Antimatter asymmetry.

Dark matter makes up around 85% of the matter in the Universe and yet we have no explanation for it in the Standard Model of particle physics. As a particle theorist, my research focuses on proposing new ideas and new tests for dark matter in order to illuminate what this mysterious stuff actually is. Recently, I have become interested in using astronomical observations of galaxies and clusters to determine whether dark matter particles interact with each other through forces other than gravity. It is remarkable that the largest structures in the Universe, millions of light years in size, can be a laboratory to study the microscopic properties of dark matter particles. I also explore the idea that dark matter is made up of strongly-interacting constituents, much like protons and neutrons. Theories of this nature cannot be worked out using paper-and-pencil and I collaborate with lattice theorists to simulate dark matter's properties using supercomputers.