Particle Nuclear Physics

At UBC, particle theorists are working on the cutting edge of understanding the universe around us. They lead and participate in major workshops, on campus and worldwide. Facilties and resources on campus include the Pacific Institute of Theoretical Physics, and the Pacific Institute for the Mathematical Sciences.

• String Theory
• Particle phenomenology
• Standard Model physics
• Quantum field theory
• Gauge theories
• Quantum Chromodynamics
• Quantum statistical mechanics
• Chiral symmetry breaking phenomena
• Overlap of particle physics and gravity
• Topics in low-energy nuclear physics
• Topological Field Theories

(Karczmarek, Ng, van Raamsdonk, Rozali, Semenoff, Sigurdsun, Zhitnitsky, plus David Morrissey at TRIUMF)

The ATLAS experiment at the Large Hadron Collider is the world's premier high-energy collider for looking for new particles at the highest energies ever probed by accelerators.   The Standard Model has several mysteries that will be probed by ATLAS.  In 2012 the LHC discovered the Higgs boson that gives particles mass.  Dark matter, seen in astronomical and cosmological observations, is missing from the Model, and these measurements suggest it could be produced and studied at the LHC.   Grand Unified Theories that unify the known forces often predict new symmetries and forces that may be evident at LHC energies.

The Belle II experiment is searching for evidence of new physics, and performing high-precision studies of Standard Model physics using electron-positron collisions at the KEK laboratory in Japan. With 100 times the data of our previous experiment BaBar,  it will produce a broad set of measurements that are sensitive to new physics at energy scales beyond the reach of existing particle colliders. These indirect measurements are complementary to the direct observations of new physics at the LHC. Belle II will also have unique abilities to search for the direct production of new particles predicted by extensions to the Standard Model, such as the Dark Sector. (Christopher Hearty, Janis McKenna).

Since the development of the highly successful Standard Model (SM) of particle physics more than 40 years ago the “Holy Grail” has been to search for processes that do not agree with the precise predictions of the SM. That the SM is not the ultimate fundamental theory of sub-atomic physics is not really in dispute since it contains more than 20 arbitrary parameters and it cannot account for the baryon asymmetry of the universe, neutrino oscillations, dark matter or dark energy. Our TREK experimental program (E36/E06), which is currently being carried out at the high-intensity 30 GeV proton synchrotron at J-PARC in Tokai, Japan, is designed to search for new physics beyond the SM. E36 is a test of Lepton Universality (e-μ) and it is a sensitive search for a SUSY extension of the SM via a precision measurement of the branching ratio:
            R_K = Γ(K⁺ → e⁺ν_e)/Γ(K⁺ → μ⁺ν_μ).

This experiment (E36) was performed at the lower beam intensity available at K1.1BR in 2015-16 and the data is currently being analyzed. E06 is a measurement of the transverse muon polarization, P_T, in the K⁺ → μ⁺π⁰ν_μ decay of stopped K⁺ mesons (K_μ3). In the SM P_T  ~ 10^-7 and there are several theoretical models which predict non-zero values as high as 10^-3. This experiment was originally proposed using a stopped K⁺ beam and a 12-sector superconducting magnet to analyze the outgoing μ⁺ and its subsequent e⁺ decay. However, due to the slow increase in the accelerator beam power we are presently evaluating a different experimental method using a segmented calorimeter which can preserve the muon polarization until it decays. This would provide a very significant increase in solid angle and allow us to make a 10^-4 to 10^-5 measurement at the current J-PARC K⁺ intensity.

The UBC TREK group ( Mike Hasinoff & TRIUMF collaborators ) was responsible for the construction of the highly-segmented scintillating-fibre stopping target at TRIUMF and we are continuing to upgrade our tracking software routines to analyze the target data.

High precision measurement of the ultra-rare kaon decay K⁺ → π⁺ + νν (KPNN) at the CERN experiment NA62 will provide one of the most incisive probes of quark flavor physics. The KPNN branching ratio is sensitive to new physics models not easily accessible by other reactions which extend the Standard Model (SM) to solve its considerable problems. The SM prediction for the KPNN branching fraction is theoretically robust at the 5% level. Only a precious few accessible 2^nd order weak interaction quark processes can be predicted with this level of certainty. The suppression of the KPNN branching fraction in the SM to the level 10^-10 allows physics beyond the SM to contribute dramatically to the branching fraction. The certainty with which the SM contribution to KPNN can be predicted permits significant discovery potential for new physics with sensitivity to probe a wide variety of models of new physics with mass scales well beyond the direct reach of the Large Hadron Collider. 

NA62 is a high-tech experiment that expects to have sensitivity for observing 80 events at the SM level for KPNN covering most of the parameter space for new physics models to contribute. It will also study many other rare or forbidden reactions to search for dark matter, heavy sterile neutrinos, neutral pion decays, and radiative processes. In addition, searches for axion-like and hidden sector particles are being investigated using an alternate mode of operation. UBC and TRIUMF groups participating in NA62 are involved in challenging hardware and analysis software projects.

The UBC rare decay group is also studying rare pion decays in the PIENU  experiment at TRIUMF. PIENU aims for an order of magnitude improvement in the precision of the ratio of pion decays to electrons and muons which sensitively probes physics beyond the SM at extremely high mass scales, and provides the best test of the SM hypothesis known as electron-muon universality. The group is also developing a new experiment PIONEER to study ulra-high precision measurements of rare pion decays aimed at testing lepton flavor universality and quark mixing. (Doug Bryman)

The SuperCDMS group at UBC and TRIUMF seeks directly detect dark matter interacting in cryogenic semiconductor detectors located deep underground at SNOLAB.  Compelling astronomical observations demonstrate that about 25% of the universe is made of dark matter, which does not consist of regular Standard Model particles and which interacts only weakly with regular matter.  By placing sensitive detectors in an ultra-clean laboratory 2km underground in Sudbury, Ontario SuperCDMS hopes to observe extremely rare collisions of dark matter particles with germanium and silicon nuclei, and by doing so to learn about the nature and interactions of the dark matter particles.SuperCDMS is currently under construction and will begin taking data in 2023.  It will have world-leading sensitivity to light dark matter particles, as well as dark photons and other exotic dark matter candidates.  The UBC group is in charge of the data acquisition and trigger systems for the experiment and is deeply involved in data analysis. UBC dark matter researchers work closely with the SuperCDMS group at TRIUMF.  (Scott Oser and TRIUMF collaborators)

Over the last four years the nEXO collaboration has developed a conceptual design for the nEXO detector, a tonne-scale neutrinoless double-beta (0νββ) decay experiment utilizing ¹³⁶Xe and conceived to be placed at SNOLAB to push the search to the next frontier. Neutrinoless double-beta (0νββ) decay has been recognized to be one of the most sensitive avenues in the search for physics beyond the Standard Model. Indeed, the observation of 0νββ decay would, in one stroke, discover lepton number violation and elementary Majorana fermions. Since the decay also requires neutrino masses to be finite, the recent discovery of neutrino oscillations has increased the interest in the search of this process worldwide. In the US the search for 0νββ decay was assigned the highest priority for new initiatives by the 2015 Long Range Planning for the nuclear physics community. The UBC/TRIUMF efforts focus on the development of advanced photodetector technologies, in particular Silicon Photomultipliers (SiPM), as well as R&D efforts for detecting the Ba ions produced in the decay of ¹³⁶Xe (Ba Tagging) (Kruecken, Dilling).

The quest for developing a unified description of all nuclei and nuclear matter and a full understanding of the origin of the heavy chemical elements as well as for testing the standard model of particle physics with precision experiments in atomic nuclei is driven by the study of nuclei far from stability. The Isotope Separator and Accelerator (ISAC) facility at TRIUMF is one of the world leading facilities for producing a wide variety of intense beams of exotic nuclei produced using the ISOL method via the bombardment of thick high-power targets with up to 100 μA of 500 MeV protons. The short-lived isotopes can be delivered to experiments using low-energy (<60 keV), available since 1999, or re-accelerated beams. For re-accelerated beams two acceleration stages are available, the first for energies of 0.15 to 1.8 AMeV since 2001, designed for high intensity RIBs for studies of nuclear reactions relevant for nuclear astrophysics, and a second stage for energies of at least 6 AMeV for masses of A<150 for nuclear reaction experiment. A wide range of experimental set-ups is available at the ISAC facility to investigate questions of current interest in nuclear astrophysics, nuclear structure and reactions, and electro-weak interaction studies, a few of which are listed here.

TRINAT uses the pressure of laser light to hold atoms of beta-decaying isotopes in a mm-sized cloud, then deduces the (otherwise invisible) neutrino momentum from the momenta of the other freely escaping products. The Standard Model prediction for the direction of neutrino emission would be perturbed by new interactions. TRINAT has made the best measurements of these effects, and the planned upgrade to 0.1% accuracy would assist the LHC's search for non-Standard Model particles by constraining (or hopefully measuring) their interactions with the first generation of quarks and leptons. A new effort will trap atoms of francium, the heaviest alkali atom (easily calculable like hydrogen), and search for new parity-violating interactions. Electromagnetism respects parity-- it is the same when reflected in a mirror-- but many new interactions don't (Behr).

The TITAN Experiment uses ion traps to carry out the most precise mass measurements on short-lived exotic isotopes. The experiment makes use of the world-leading on-line facility ISAC at TRIUMF on UBC campus to help test the Standard Model and test modern theoretical models that connect nuclear forces with underlying fundamental strong interaction. Nuclear astrophysics and nucleosynthesis are the other driving motivations for the experiments at TITAN (Dilling).

Excited states in exotic nuclei are studied via gamma-ray spectroscopy following beta decay, with the GRIFFIN spectrometer, or nuclear reactions, with the TIGRESS spectrometer. These powerful microscopes provide insights into the nuclear dynamics and shell structure far away from stability and test modern theoretical models that connect nuclear forces with the underlying fundamental strong interaction. The IRIS solid hydrogen target experiment enables reaction studies even further away from stability using lower intensity radioactive ion beams. Aside from studying the nature of atomic nuclei this suite of experiments is also essential for the study of nuclei that play a role in the astrophysical r-process, which is responsible for the synthesis of half the chemical elements from iron to uranium. The study of these nuclei in the laboratory, combined with astrophysical simulations and the new era of multi-messenger astronomy, will help elucidate the origin of the heavy elements in the universe (Kruecken).

TRIUMF is Canada's main centre for accelerator and beam physics expertise.  UBC graduate students (and co-op or summer undergradutae students) may participate in research projects with TRIUMF physicists, either in developing or adding to the lab's existing accelerators and particle beams, or in collaboration with other laboratories.

Projects for the TRIUMF 500-MeV cyclotron include:

• Easing space-charge limitations on cyclotron performance: a full-scale model of a cyclotron's central region is available for studying the critical first few turns, and as a test stand for developing high intensity H‾ ion sources;
• Theoretical charged-particle optics, using various techniques from classical mechanics, including Lie Algebra and symplectic integrators;
• Electro-magnetic modeling of the rf accelerating structure, which consists of 80 separate resonators (right), permitting excitation of undesirable high-order modes. To better understand and suppress these, a 3-D electrodynamic model is being developed.

Current projects for the ISAC Isotope Separator and Accelerator include:

• A new front-end with the capability of accelerating singly-charged ions with A≤150 from source potential to 150 keV/u. This will require a low-energy transport beamline, two RFQ accelerators and a gas-stripper;
• Superconducting rf cavity development, prototyping and research, including development of ancillary rf and control equipment;
• Design of a room-temperature drift-tube linac for accelerating ions with A/q ≤ 30 from 150 keV/u to 400 keV/u;
• Diagnostics for very-low-intensity ion beams.

TRIUMF physicists are also participating in the EMMA project - a 20-MeV electron model of a 20-GeV muon accelerator. This is a novel type of FFAG accelerator that has been designed by an international collaboration (and is being built at Daresbury Laboratory in the UK) to test the feasibility of abandoning the restrictive "scaling" principle traditionally observed in FFAG design. This type of accelerator, which offers very high pulse rates and beam intensities, is of great current interest for neutrino factories, muon colliders, neutron sources, industrial irradiation, driving sub-critical reactors, and cancer therapy with ion beams (which offer better dose localization than X-rays). For the latter application TRIUMF is also developing new beam dynamics software for the design of small-aperture proton or carbon FFAGs suitable for hospitals.

ALPHA is an international collaboration based at CERN that produces and traps antihydrogen atoms, the antimatter counterpart of the simplest atom, hydrogen. By precise comparisons of hydrogen and antihydrogen, the experiment tests fundamental symmetries between matter and antimatter. The Canadian group (ALPHA-Canada) including Hardy (UBC), Hayden (SFU), and several TRIUMF physicists, contributes to both the particle physics and atomic spectroscopy aspects of the experiment, from ion and atom trapping, to manipulation of cold plasmas, to precision laser and microwave spectroscopy, and sophisticated particle physics detection and analysis. Hence it is an excellent training ground for students. Graduate students typically spend up to several months a year in Geneva to participate in the experiment. To date, ALPHA has measured the 1S-2S atomic transition in antihydrogen to an accuracy of about 2 parts in 10¹², as well as measurements on the 1S-2P atomic transition, and hyperfine transitions. Current work focuses on measuring the effect of gravity on antimatter.

For the graduate student, these projects offer a great opportunity to work at the worlds leading particle physics facilities. Although some particle physics collaborations may be large, we do work in small groups, alongside peers from all parts of the world. Students have the opportunity to gain expertise in many different areas, from high-speed computing to large-scale engineering. While TRIUMF is Canada's national laboratory for particle physics, students may have the opportunity to conduct their research and to spend some time living and working at major physics laboratories andfacilities around the world: in Switzerland, California, Chicago, Japan, and Northern Ontario. Graduate students will typically be offered opportunities to present their research at national and international conferences.

For more detailed information about ongoing Subatomic theory research, please consult the Professors' web pages directly.