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.

Higgs boson’s coupling to top quark; neutrino interactions and mixing; astronomical neutrinos; machine learning for high-energy physics; particle detector development; silicon tracking detectors; data acquisition systems for high-energy physics

Understanding how elementary particles interact with each other is a massive challenge. Literally. Particles of matter obtain their masses via interaction with the Higgs field, present everywhere and acting as a slowing down mechanism. Its associated particle, the Higgs boson, interacts with fermions proportionally to their masses. So far the majority of measurements of Higgs boson properties is in agreement with the Standard Model (SM) of particle physics. This widely accepted theory yields very accurate predictions, yet it fails to explain why for instance the mass of the Higgs boson itself is so light.
One aspect of my research is to perform precise studies of the Higgs boson’s interaction with the heaviest particle of matter: the top quark. The parameter of interest, called interaction strength or coupling, is very sensitive to new physics and any deviation with respect to the theoretical prediction would uncover non-​SM phenomena. At the Large Hadron Collider (LHC) at CERN in Switzerland, it is possible to access this parameter via a rare Higgs boson production mode that has recently been discovered: the Higgs boson production in association with a top quark pair, or “ttH”. I contributed to the discovery of ttH by the ATLAS experiment, one of the LHC’s detectors. I am now interested in deploying advanced machine learning techniques to increase the sensitivity of the ttH analysis, leading to a more precise assessment that could uncover new physics.

On the other end of the spectrum, the lightest particles of matter are the mysterious neutrinos. They are expected to be massless in the SM yet they oscillate, that is to say they change flavors over time, and this ‘mixing’ is only possible if their mass is non-zero. A leading-edge experiment for neutrino science hosted by Fermilab in the United States is being built to operate starting in 2026: the Deep Underground Neutrino Experiment (DUNE). It will consist of two massive state-of-the-art neutrino detectors, one at Fermilab in Illinois and one at the Sanford Underground Research Facility in South Dakota, 1.5 km underground. The Long-Baseline Neutrino Facility (LBNF) will supply intense beams of neutrinos and antineutrinos with energy spectra broader than any other current experiment. DUNE is designed both for big potential discoveries as well as precision measurements. An exciting feature of DUNE is its sensitivity to neutrinos coming from the cosmos, especially stellar explosions: supernovae. As a member of the DUNE Collaboration, my initial interests focus on developing a robust data acquisition system to store the enormous amount of information to record neutrinos from supernovae. This will enable us to understand more about neutrinos and at the same time about the cosmological phenomenon of core-collapsing stars.

Besides data analysis, I am involved in hardware work related to the construction of the future ATLAS inner tracking detector designed for the High-Luminosity phase of the LHC that will run 2026-3037. The collision rate (and radiation damage) will be at least 7 times larger than it has been up until now. I plan to set up test benches of the data acquisition system of this future tracker and translate this expertise to benefit the DUNE experiment.

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.

Neutrino masses and mixing; Neutrino interactions with nuclei.

My research aims to understand the neutrino, the most abundant particle in the universe that has any mass. Because the neutrino almost never interacts, we know very little about it. However, that same characteristic also means that we can study them by making a beam of neutrinos and shooting them long distances through the earth and studying their composition after they have had time to evolve over time. These measurements can tell us more precisely what the mass differences are between different neutrinos, whether their masses are like the charged fermion mass spectra or the inverse, and whether neutrinos and antineutrinos evolve the same way over time. Because neutrinos have mass, they have a huge impact on galaxy formation in the universe, and if neutrinos and antineutrinos evolve differently, they may be the reason that the universe today is dominated by matter rather than simply being full of light from matter-antimatter annihilations.

The Deep Underground Neutrino Experiment (DUNE) combines an enormous fine-grained neutrino detector with an intense broad-band neutrino beam that has traveled over 1300 km by the time it reaches that detector. DUNE will enable us to test the neutrino oscillation framework at a level of detail and precision that is simply not possible with today’s suite of very capable narrow-band neutrino beam experiments. I will be working on DUNE’s near detector, because the best predictions for what the far detector will see come from an accurate (and tested) description of how neutrinos interact and from extensive measurements from the DUNE Near Detector Complex. My ultimate research plan is to do precision oscillation measurements on DUNE.

However, just as the detector and beamline for DUNE are not yet ready today, the field of neutrino physics as a whole is not yet ready to predict oscillated neutrino event rates over a broad range of energies at the required level of precision. In order to fulfill DUNE's promise of precision we not only have to build the detector and neutrino beamline, but we also have to understand the way neutrinos will interact in that detector. The MINERvA experiment, located at Fermilab, has started writing the book on neutrino interactions and how the nuclear environment affects those interactions. We have collected a huge sample of neutrino and antineutrino interactions on many different nuclei, and are able to shine a much brighter light on neutrinos than ever before. I am currently the co-spokesperson of MINERvA and I am making sure many more neutrino interaction measurements come from MINERvA to best prepare for DUNE.

Neutrinos, especially neutrino mixing; Antimatter; Charge-Parity (CP) violation.

Experimental observations of neutrino oscillations through the mixing of their mass and flavour states have established that neutrinos have mass. Recently, T2K and other experiments have established the mixing of neutrinos through the third and smallest mixing angle, which opens the door for Charge-Parity (CP) violation in neutrino oscillations. If CP violation is present, neutrinos and their antimatter counterparts, antineutrinos, will oscillate differently. This CP violation signature can be observed by experiments which produce beams of muon neutrinos (antineutrinos) that oscillate to electron neutrinos (antineutrinos). To this end, I am participating in the T2K experiment, which aims a beam of muon neutrinos produced at the J-PARC accelerator facility in Japan towards the Super-Kamiokande detector that is 295 km away. By observing muon neutrino to electron neutrino oscillations, we are able to make precision measurements of neutrino oscillation parameters. I am particularly interested in the ability of T2K to search for CP violation by producing a beam of antineutrinos, as well as future experiments such as Hyper-K that will more precisely measure the amount of CP violation.

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.