Events List for the Academic Year

Event Time: Monday, July 29, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 301, Hennings Bldg
Add to Calendar 2019-07-29T13:00:00 2019-07-29T15:00:00 Departmental Oral Examination (Thesis Title: "Exploring the tumour microenvironment with non-invasive magnetic resonance imaging (MRI) techniques") Event Information: Abstract: This thesis comprises development and application of several MRI techniques to improve our understanding of tumour growth, drug distribution, and drug effect using pre-clinical tumour models in mice. In the first part of the thesis, a novel high molecular weight contrast agent, HPG-GdF is introduced. This molecule is a hyperbranched polyglycerol labeled with an MRI contrast agent (Gd-DOTA) as well as a fluorescent tag. After injecting the agent into mice within an MRI scanner, contrast-agent kinetics were quantified using a two-parameter linear model and validated with quantitative immunohistochemistry via direct fluorescence imaging of HPG-GdF. HPG-GdF was used to assess whether vascular function plays a role in how a chemotherapy (Herceptin) distributes within a tumour. Tumour vessel permeability and fractional plasma volume were quantified using the HPG-GdF and no relationship was found between vascular function and presence of drug. HPG-GdF was then applied to show that Avastin (an antiangiogenic agent) decreased vessel permeability in tumours. Using histological methods, a dramatic reduction in hypoxia (oxygen deficiency in tissues) was observed in treated tumours. Unfortunately, existing MRI methods to evaluate oxygenation were time-intensive and lacked sensitivity. In the second part of this thesis, we introduce, develop, validate, and apply a new method to assess tumour oxygenation using MRI. Oxygen (O2) is a paramagnetic molecule that shortens the longitudinal relaxation time (T1) of protons in MRI. This subtle effect has been widely reported in the literature but its applications in cancer have been limited. Our technique - dynamic oxygen-enhanced MRI (dOE-MRI) - uses T1 weighted signal intensity images acquired during a cycling gas challenge (air or oxygen) and independent component analysis (ICA). Hypoxia staining with pimonidazole correlated strongly with dOE-MRI values in a murine tumour model (SCCVII) and only weakly in a colorectal xenograft model (HCT-116). Finally, we provide compelling evidence that treatment with Avastin improves tumour oxygenation in subcutaneous tumours. With dOE-MRI the sensitivity and speed of existing techniques was greatly improved. Since our technique requires no injectable contrast agent, special sequences or hardware, we anticipate that this technique can be quickly translated into the clinic. Event Location: Room 301, Hennings Bldg
Event Time: Monday, July 29, 2019 | 8:00 am - 10:00 am
Event Location:
ISAC-II Room 223 (TRIUMF)
Add to Calendar 2019-07-29T08:00:00 2019-07-29T10:00:00 Departmental Oral Examination (Thesis Title: "Dawning of Nuclear Magicity in N=32 Seen Through Precision Mass Spectrometry") Event Information: Abstract: In the early days of nuclear science, physicists were astounded that specific "magic" combinations of neutrons or protons within nuclei seemed to bind together more tightly than other combinations. This phenomenon was related to the formation of shell structures in nuclei. More recently, nuclear shells were observed to emerge or vanish as we inspect nuclei further from stability. The structural evolution of these changing shells has been the object of intense experimental investigation, and their behavior has become a standard ruler to benchmark theoretical predictions. In this work, we investigated the emergence of shell effects in systems with 32 neutrons (N=32) using mass spectrometry techniques. Evidence for "magicity" was observed in potassium (with 19 protons, or Z=19), calcium (Z=20) and scandium (Z=21), but not in vanadium (Z=23) and heavier elements. In between, the picture at titanium (Z=22) was unclear. We produced neutron-rich isotopes of titanium and vanadium through nuclear reactions at the ISAC facility and measured their atomic masses at the TITAN facility, in the TRIUMF Laboratory in Vancouver.  These measurements were performed with the newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer at TITAN facility and were substantiated by independent measurements from the Penning trap mass spectrometer. The atomic masses of 52Ti to 55Ti and 52V to 55V isotopes were measured with high precision, right at the expected emergence of N=32 shell effects.  Our results conclusively establish the existence of weak shell effects in titanium and confirm their absence in vanadium, narrowing down the precise onset of this shell closure. Calculations of the N=32 nuclear shell are within reach of the so-called "ab initio" theories. In these, complex atomic nuclei are described theoretically from fundamental principles, by applying principles of Quantum Chromodynamics to many-body quantum methods. Our data were compared with a few state-of-the-art ab initio calculations which, despite very successfully describing the N=32 shell effects in Ca and Sc isotopes, overpredict its strength in Ti and erroneously assign V as its point of appearance. We hope the deficiencies revealed by our work will guide the development of the next generation of ab initio theories. Event Location: ISAC-II Room 223 (TRIUMF)
Event Time: Thursday, July 25, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
Add to Calendar 2019-07-25T13:00:00 2019-07-25T15:00:00 Final PhD Oral Examination (Thesis Title: “Aspects of Quantum Information in Quantum Field Theory and Quantum Gravity”) Event Information: Abstract: We discuss applications of quantum information theoretic concepts to quantum gravity and the low-energy regime of quantum field theories. The first part of this thesis is concerned with how quantum information spreads in four-dimensional scattering experiments for theories coupled to quantum electro- dynamics or perturbative quantum gravity. In these cases, every scattering process is accompanied by the emission of an infinite number of soft photons or gravi-tons, which cause infrared divergences in the calculation of scattering probabilities. There are two methods to deal with IR divergences: the inclusive and dressed formalisms. We demonstrate that in the late-time limit, independent of the method, the hard outgoing particles are entangled with soft particles in such a way that the reduced density matrix of the hard particles is essentially completely decohered. Furthermore, we show that the inclusive formalism is ill-suited to describe scattering of wavepackets, requiring the use of the dressed formalism. We construct the Hilbert space for QED in the dressed formalism as a representation of the canonical commutation relations of the photon creation/annihilation algebra, and argue that it splits into superselection sectors which correspond to eigenspaces of the generators of large gauge transformations. In the second part of this thesis, we turn to applications of quantum information theoretic concepts in the AdS/CFT correspondence. In pure AdS, we find an explicit formula for the Ryu-Takayanagi (RT) surface for special subregions in the dual conformal field theory, whose entangling surface lie on a light cone. The explicit form of the RT surface is used to give a holographic proof of Markovicity of the CFT vacuum on a light cone. Relative entropy of a state on such special subregions is dual to a novel measure of energy associated with a timelike vector iiiflow between the causal and entanglement wedge. Positivity and monotonicity of relative entropy imply positivity and monotonicity of this energy, which yields a consistency conditions for solutions to quantum gravity. Event Location: Room 203, Graduate Student Centre (6371 Crescent Road)
Event Time: Monday, July 22, 2019 | 3:00 pm - 5:00 pm
Event Location:
UBC Sage Restaurant (Leon and Thea Koerner University Centre, 6331 Crescent Road Vancouver BC, V6T 1Z2)
Add to Calendar 2019-07-22T15:00:00 2019-07-22T17:00:00 Don Witt Celebration of Life Event Information: A celebration of Don Witt's life will be hosted at the UBC Sage Restaurant (Leon and Thea Koerner University Centre, 6331 Crescent Road Vancouver BC, V6T 1Z2) on Monday, July 22, 2019 at 3pm. Please RSVP via the link below. RSVP for Don Witt's Celebration of Life Leave a message on Don's Memorial Page Event Location: UBC Sage Restaurant (Leon and Thea Koerner University Centre, 6331 Crescent Road Vancouver BC, V6T 1Z2)
Event Time: Friday, July 19, 2019 | 10:00 am - 12:00 pm
Event Location:
Room 309, Hennings Bldg
Add to Calendar 2019-07-19T10:00:00 2019-07-19T12:00:00 Departmental Oral Examination (Thesis Title: "High Resolution Two-Photon Spectroscopy of 129Xe for Precision Optical Magnetometry") Event Information: Abstract: This dissertation presents high precision two-photon xenon spectroscopy of the 5p5(2P3/2)6p 2[3/2]2 -> 5p6 (1S0) transition. Experimental results of the spectroscopic signal over pressures of 15 980 mTorr, combined with a theoretical discussion, led to the determination of the natural linewidth of the excited state. Specific attention is payed to the (F = 3/2) hyperfine level of 129Xe, motivated by the new experiment at TRIUMF to measure the electric dipole moment of the neutron (nEDM), where 129Xe will be used as an optical comagnetometer. A non-zero value of the nEDM would partially confirm the existence of the baryon asymmetry in the universe as predicted by the standard model. The experiment at TRIUMF aims increase the sensitivity of the current nEDM limit by increasing the number of ultra-cold neutrons and employing a cohabiting 199Hg/129Xe dual species comagnetometer. The first experimental success was the technological development of the continuous wave 252 nm ultra-violet (UV) laser system, with the power and precision to selectively probe the hyperfine levels of 129Xe. Using this laser system the first high resolution spectrum of the two-photon transition was measured. Ten transition peaks are observed for the six most abundant isotopes in xenon gas, along with the hyperfine levels of the 129Xe and 131Xe isotopes. Analysis of this spectrum led to direct determinations of the hyperfine constants of the 5p5(2P3/2)6p2[3/2]2 excited state and constants relating to the isotope shift. The final part of the dissertation focused on the parameterization of the 129Xe (F = 3/2) spectral line. In the nEDM experiment the pressure of 129Xe is limited to 3 mTorr, making it essential to characterize the signal at this level in order to maximize the sensitivity of the comagnetometer. This work presents a pressure dependence study of the spectral lineshape from 980-15 mTorr. These results illustrate the expected signal size and relative transition frequency to the (F = 3/2) level for precision laser tuning. In addition to the contributions of this work to optical magnetometry, the results present a complimentary experimental technique to determine the natural linewidth of the 5p5(2P3/2)6p2[3/2]2 excited state. The high precision of the results permit extrapolation of the lineshape to zero pressure yielding a natural linewidth of 4.3(1.6) MHz/Torr. Overall, the work presented is significantly important to optical magnetometry in nEDM experiments, as well as to precision spectroscopy and theories of atom-atom interactions. Event Location: Room 309, Hennings Bldg
Event Time: Thursday, July 18, 2019 | 2:00 pm - 3:30 pm
Event Location:
Brimacombe 311
Add to Calendar 2019-07-18T14:00:00 2019-07-18T15:30:00 CM Seminar: Three superconducting phases of 1111-type iron-based superconductor RFeAs1-xPnxO1-y(F,H)y (R=La and Nd, Pn=P and Sb) Event Information: In one of 1111-type iron-based superconducting (SC) system LaFeAsO, the electron doping level and the local crystal structure can be controlled by the F/H substitution for O and P for As. By these chemical substitution effects, Fermi surface (FS) topology has been changed, and three different SC phases appears in LaFeAs1-xPxO1-y(F/H)y system. [1,2] The first and second SC phases (SC1 and SC2) are observed in the low F concentration region around LaFeAsO0.9F0.1 ((x, y) ~ (0, 0.1)) and LaFeAs0.6P0.4O0.9F0.1 ((x, y) ~ (0.4, 0.1)), respectively. On the other hand, the third SC phase (SC3) appears in the highly electron doping region of (x, y) ~ (0, 0.3). In the SC1 and SC2 states, the spin fluctuations due to the FS nesting in LaFeAsO-type FS with xy hole FS or LaFePO-type FS without xy hole FS play an important role in order to stabilize the superconductivity. [3,4] In the SC3 state, however, the heavily electron doping destabilizes the FS nesting. In this SC3 phase, the next nearest neighbor magnetic interaction in the xy direction in real space induces the superconductivity. We also have investigated the transport properties and structural parameters of NdFeAs1-xPxO1-y(F/H)y (y=0~0.4) and LaFeAs1-xSbxO1-y(F/H)y (y=0~0.3) to clarify the correlation between the stability of superconductivity and the change of the FS accompanied by the P/Sb and F/H substitutions. In the Nd-1111 system with P substitution, the result of structural analysis revealed that the pnictogen height from the Fe plane hPn is larger than that in the La-1111 system. The Sb substitution in the La-1111 system also increases hPn. With increasing hPn, the FS nesting has been improved by the enlarging the xy FS near RFeAsO in the phase diagram, and the strength of the next nearest neighbor magnetic interaction is also enhanced in heavily H doping region. As a result, these effects has stabilized the SC1 and SC3 states, and merges the SC1 phase near RFeAsO and the SC3 one in the highly H doping region in the phase diagram. The phase diagram for the present systems can be explained by the scenario for FS nesting and next nearest neighbor magnetic interaction.   [1] S. Miyasaka et al., Phys. Rev. B 95, 214515 (2017). [2] K. T. Lai, S. Miyasaka et al., Phys. Rev. B 90, 064504 (2014). [3] S. Miyasaka et al., J. Phys. Soc. Jpn. 82, 124706 (2013). [4] A. Takemori, S. Miyasaka et al., Phys. Rev. B 98, 100501(R) (2018). Event Location: Brimacombe 311
Event Time: Wednesday, July 17, 2019 | 2:00 pm - 3:00 pm
Event Location:
BRIM 311
Add to Calendar 2019-07-17T14:00:00 2019-07-17T15:00:00 Majorana-Hubbard Model on the Triangular Lattice Event Information: Of late, there has been a growing body of experimental work that brings us closer to an undoubted realization of Majorana fermions in condensed matter systems. In two-dimensions these quasiparticles arise as zero energy vortex bound states on the surface of a topological superconductor. And in the presence of a lattice of these vortices, interactions between these Majorana zero modes (MZMs) fall off exponentially with the superconducting coherence length. This motivates the construction of a tight-binding model to describe the low energy physics. Given that the vortex lattice usually has a triangular geometry, we study the role of interactions in this setup using a combination of mean field theory and numerical simulation of ladder variants of the model using the density-matrix renormalization-group technique. Our analysis indicates an interaction driven phase transition into a critical phase. Event Location: BRIM 311
Event Time: Monday, July 8, 2019 | 9:00 am - 11:00 am
Event Location:
Room 200, Graduate Student Centre (6371 Crescent Road)
Add to Calendar 2019-07-08T09:00:00 2019-07-08T11:00:00 Final PhD Oral Examination (Thesis Title: “Personalized Dosimetry Protocol for the Optimization of Lutetium-177 Dotatate Radionuclide Therapy”) Event Information: Abstract: Targeted radionuclide therapy has been shown to be one of the most effective treatment options for metastatic neuroendocrine tumours (NETs). In particular, peptide receptor radionuclide therapy (PRRT) with Lutetium-177 (177Lu) labeled DOTATATE results in significantly improved tumour control, while only low to moderate normal tissue toxicity. There is growing evidence that the efficacy of this treatment can be further improved by performing personalized administration of radiopharmaceutical. However, since dosimetry for PRRT is usually considered challenging, traditionally NET patients are treated with same or very similar amounts of 177Lu DOTATATE. The objective of this thesis was to propose a simple, yet accurate dosimetry protocol, which could be easily implemented in clinics for the optimization of 177Lu DOTATATE radionuclide therapy. To achieve this aim, the following physics questions, that are related to image-based dose calculation, were investigated: The performance of camera calibration method using simple planar scans, was compared to that obtained from tomographic acquisitions. To assess the quantitative accuracy of commercial SPECT reconstruction software (Siemens Flash3D), a number of phantom experiments with different photon attenuation conditions were performed. The influence of camera dead-time correction on the estimated dose was investigated. The kidney doses obtained from four time-activity curve creation methods using three data points were compared. In order to simplify the dosimetry, the accuracy of dose estimated based on two data points, or even potentially one data point, was evaluated. Our results show that gamma camera can be accurately calibrated with planar scan of a point-like source. The error of 177Lu activity quantification in large volume (>100mL) was about 5% when proper segmentation was applied to Siemens Flash3D reconstructions. Dead-time correction was found to have no impact on the estimated dose. Kidney dose estimated based on single data measured at 48-72 hours produced small error (<10%) for the majority of patients, thus could be recommended for clinical use. This single data point method can also be applied to other organ, as long as its bio-kinetics can be described by a monoexponential function and the statistical behavior of the population effective half-lives in that organ has been estimated. Event Location: Room 200, Graduate Student Centre (6371 Crescent Road)
Event Time: Monday, July 8, 2019 | 9:00 am - 4:00 pm
Event Location:
Hennings
Add to Calendar 2019-07-08T09:00:00 2019-08-02T16:00:00 Phenomenal Physics Summer Camp Event Information: Event Location: Hennings
Event Time: Wednesday, July 3, 2019 | 10:30 am - 12:00 pm
Event Location:
Henning 318
Add to Calendar 2019-07-03T10:30:00 2019-07-03T12:00:00 Contemporary particle physics with ultracold neutrons at TRIUMF Event Information: In this presentation I will introduce the new ultracold neutron (UCN) facility which has been commissioned at TRIUMF on South UBC campus in 2017. UCN are free neutrons which move at very low speeds, thus they behave like a gas and can be stored and observed for macroscopic periods of time (order ~100s). This enables us to investigate their fundamental properties to unprecedented precision and challenge our current understanding of the underlying symmetries and interactions by probing the standard model of particle physics and beyond. In particular, the Japanese-Canadian TUCAN (TRIUMF UltraCold Advanced Neutron) collaboration aims at searching for a neutron electric dipole moment. Measuring or improving the sensitivity for this elusive quantity would help us understand why there is so much more matter in the universe than antimatter, which is the basis of our existence as human mankind. An imminent upgrade of TRIUMF’s UCN facility will not only allow TUCAN to do so competitively, but also prospectively enable UCN researchers to perform many other exciting experiments with impact on modern physics questions - adressing the field of low energy/high precision physics which is complementary to e.g. collider physics. I will give some further examples of such experiments as well as briefly highlight overlaps with related applied techniques which TUCAN and other UCN groups rely on such as: nuclear magnetic resonance, atomic physics, high precision magnetometry, neutron optics, superfluid helium cryo technology etc.   BIO During her Bachelor’s and Master’s degree studies, Beatrice Franke was involved in different experiments with ultracold neutrons which were based at TUM in München, Germany. She obtained her PhD from ETH Zürich, while being employed as doctoral student at PSI in Villigen, Switzerland, where she continued to perform research with ultracold neutrons. She developed specialized expertise in the observation and manipulation of magnetic fields with respect to their homogeneity and stability. Those are very important tools in high precision experiments, and additionally allowed her to search for and constrain exotic interactions mediated by axionlike particles. Later Beatrice moved on to a postdoctoral appointment at the MPQ in Garching, Germany, where she took part in laser spectroscopy of light muonic atoms. Such systems are highly sensitive to the structural properties of the nucleus to which the muon is bound. She studied the intricacies of these systems such as muon-specific quantum electro dynamics, nuclear polarizability, and geometry dependence of quantum interference in laser spectroscopy. Since now three years she holds an NSERC elegible research scientist position at TRIUMF, where she has switched her scientific focus back to ultracold neutrons. Currently mainly involved in the design of a next generation spectrometer for the search of a non-zero electric dipole moment of the neutron..   Event Location: Henning 318
Event Time: Wednesday, July 3, 2019 | 9:00 am - 11:00 am
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
Add to Calendar 2019-07-03T09:00:00 2019-07-03T11:00:00 Final PhD Oral Examination (Thesis Title: “Monte Carlo Modelling of Peripheral Dose and Risk of Secondary Malignancy in Flattening-Filter-Free and 10 MV Photon Beams for Paediatric Radiotherapy”) Event Information: Abstract: One of the most serious late side effects of cancer treatments is the development of a second malignant neoplasm (SMN). While the risk of SMN is influenced by many factors, radiation therapy (RT) during childhood and adolescence has been shown to be one of the most significant factors associated with the development of a second cancer. The work presented in this thesis aims at determining how to minimize the risk of RT-induced SMN without affecting the quality and efficacy of RT treatments. To properly assess dose to the entire body in patients, a Monte Carlo and measurements based model was developed. This model was used to determine the dose delivered to a cohort of pediatric patients by three different photon radiotherapy treatment modes: 6MV flattened, 6MV flattening-filter-free (FFF) and 10MV FFF. To establish the clinical significance of the dose difference between the three modes, the risk of SMN as calculated by four different risk models were assessed for whole lung irradiation (WLI), a treatment used to treat lung metastases in pediatric patients. The mixed Monte Carlo and measurements model was found to be accurate. The uncertainty on the dose was found to be below 9.4 % of the local dose. A comparison of the out-of-field dose delivered by the 6MV FFF and 10MV FFF beams relative to the 6MV flattened beam was presented. The data demonstrated dose reductions of 3.9% (95% CI[2.1,5.7]) and 9.8% (95% CI[8.0, 11.6]) at 5 cm from the planning treatment volume (PTV) and 21.9% (95% CI[13.7, 30.1]) and 25.6% ( 95% CI[17.6,33.6]) at 30 cm for 6MV FFF and 10 MV FFF beams respectively compared to the 6MV flattened beam. In pediatric patients who were treated with WLI, this dose reduction lead to a risk ratio of <0.90 and <0.95 for 10 MV FFF and 6MV FFF respectively compared to the 6MV flattened beam. In conclusion, the work presented in this thesis provides evidence that FFF beams, specifically 10MV FFF beams, deliver lower out-of-field dose than 6MV flattened beams. For WLI treatments, this dose reduction reduces the estimated risk of RT-induced thyroid cancers. Event Location: Room 203, Graduate Student Centre (6371 Crescent Road)
Event Time: Tuesday, June 25, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 318, Hennings Bldg.
Add to Calendar 2019-06-25T14:00:00 2019-06-25T16:00:00 Departmental Oral Examination (Thesis Title: "Search for New High-Mass Phenomena in Events with Two Muons using the ATLAS Detector at the Large Hadron Collider") Event Information: Abstract: Although elementary particles and their interactions are extremely well modeled by the Standard Model of particle physics, some experimental measurements cannot be explained entirely by this theory. Many extensions of the Standard Model predict the existence of new phenomena at high energies. In particular, new resonance models and contact interaction models leading to dimuon final states are numerous. This dissertation presents a search for new high-mass phenomena in events with two muons using the ATLAS detector at the Large Hadron Collider. The search results are found to be consistent with the Standard Model background prediction. Interpretations both in the context of resonant and non-resonant new physics models are carried out. In particular, lower limits on the mass of hypothetical Z' bosons are set between 4.0 TeV for the Z'SSM model and 3.3 TeV for the Z'ψ model, and lower limits on the contact interaction energy scale Λ are set between 18 TeV and 30 TeV, depending on the chiral structure of the contact interaction. In addition to data analysis at the energy frontier, the performance of muon reconstruction and identification within the ATLAS experiment is detailed. More precisely, calculations of muon trigger scale factors for high-pΤ muons using events containing a leptonically decaying W boson and jets are presented. A new muon identification working point is also investigated. Finally, as the ATLAS experiment enters its second long shutdown, the first layer of the endcap regions of the muon spectrometer will be replaced with the New Small Wheels (NSWs) in order to improve both the triggering and tracking capabilities of the ATLAS detector. One of the two main technologies used in the NSW is small-strip Thin Gap Chambers (sTGCs). Work carried out with the sTGC collaboration, which aims to characterize and integrate the NSW into the ATLAS detector in the coming years, is described. Particularly, results of various test beam campaigns carried out at Fermilab and at CERN are presented. Position resolution measurements of less than 50μm are obtained. Measurements using the latest electronics readout chain of the sTGC detectors under realistic conditions are also presented. Event Location: Room 318, Hennings Bldg.
Event Time: Friday, June 21, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 318, Hennings Bldg.
Add to Calendar 2019-06-21T14:00:00 2019-06-21T16:00:00 Departmental Oral Examination (Thesis Title: "Search for the production of Higgs bosons in association with top quarks and decaying into bottom quark pairs with the ATLAS detector") Event Information: Abstract: The Standard Model of particle physics (SM) describes mass generation of fundamental particles via the Brout-Englert-Higgs mechanism. It predicts Yukawa interactions between the Higgs boson and fermions, with interaction strengths proportional to the fermion masses. The largest Yukawa coupling is that of the top quark, and its value has implications in particle physics and beyond. As the SM is not a complete theory of nature, detailed measurements of its predictions are a mandatory step towards improving the understanding of nature. This dissertation presents a search for Higgs boson production in association with a top quark pair, a process directly sensitive to the top quark Yukawa coupling. The search uses 36.1 fb−1 of data at √s = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider (LHC) in 2015 and 2016. It is designed for Higgs boson decays to bottom quarks, and decays of the top quark pair resulting in one or two electrons or muons. The discrimination between the signal Higgs boson production process and background processes, dominated by the production of top quark pairs, is performed with multivariate analysis techniques. The matrix element method is used and optimized for this search. Possible machine learning extensions of the method are investigated to help overcome its large computational demand. The obtained ratio of the measured cross-section for the signal Higgs boson production process to the prediction of the SM is µ = 0.84 (+0.64, −0.61). The expected sensitivity of an extension of the search, using 139.0 fb−1 of data collected between 2015–2018, is 3.3σ. Data collected between 2016–2018 is also used in a measurement of the ATLAS muon trigger system efficiency. A statistical combination of searches for Higgs bosons produced in association with top quark pairs is performed, including the search for Higgs boson decays to bottom quarks and additional final states. The combination results in the observation of this Higgs boson production process with an observed significance of 5.4σ, compared to an expected sensitivity of 5.5σ. It experimentally establishes Yukawa interactions in the SM. Event Location: Room 318, Hennings Bldg.
Event Time: Thursday, June 20, 2019 | 12:30 pm - 2:30 pm
Event Location:
Room 301, Hennings Building
Add to Calendar 2019-06-20T12:30:00 2019-06-20T14:30:00 Final PhD Oral Examination (Thesis Title: “Dirac Materials and the Response to Elastic Lattice Deformation”) Event Information: Abstract: Dirac materials have formed a thriving and prosperous direction in modern condensed matter physics. Their bulk bands can linearly attach at discrete points or along curves, leading to arc or drumhead surface states. The candidate Dirac materials are exemplified by Dirac/Weyl semimetals, Dirac/Weyl superconductors, and Dirac/Weyl magnets. Owing to the relativistic band structure, these materials have unique responses to the applied elastic crystalline lattice deformation, which can induce pseudo-magnetic and pseudo-electric fields near the band crossings and produce transport distinguished from that caused by ordinary magnetic and electric fields. In this dissertation, I will demonstrate exotic transport due to the strain-induced gauge field in Weyl semimetals, Weyl superconductors, and Weyl ferromagnets. I will first elucidate that a simple bend deformation can induce a pseudo-magnetic field that can give rise to the Shubnikov-de Haas oscillation in Weyl semimetals. Then I will elaborate that strain can Landau quantize charge neutral Bogoliubov quasiparticles as well and result in thermal conductivity quantum oscillation in Weyl superconductors. Lastly, I will consider the strain-induced gauge field beyond the fermionic paradigm and explain various quantum anomalies of magnons in Weyl ferromagnets. Event Location: Room 301, Hennings Building
Event Time: Wednesday, June 19, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 309, Hennings Bldg.
Add to Calendar 2019-06-19T13:00:00 2019-06-19T15:00:00 Departmental Oral Examination (Thesis Title: "Studies of atmospheric properties for optical ground-based Astronomy and methods for laser guide star adaptive optics performance increase") Event Information: Abstract: Ground-based Astronomy suffers from wavefront distortion by the turbulent atmosphere, preventing telescopes to reach diffraction-limited resolution. Modern large telescopes and next generation extremely-large telescopes use or will use adaptive optics systems with laser guide stars to correct for atmospheric wavefront distortion. The first part of the thesis deals with astronomical site testing and the second part with methods for adaptive optics system improvement. Meteorological data for 15 observatory sites have been studied. Monthly averages of cloud cover, wind speed at 200 hPa, precipitable water vapour, vertical wind velocity and aerosol index have been compared for the sites. The longterm evolution over 45 years of these five atmopsheric quantities was investigated. Site testing campaigns aim at the characterization of potential telescope sites in terms of optical turbulence. Using scintillometers, ground layer turbulence profiles can be measured. For an assessment of sites long-term statistics are needed. Two campaigns for daytime and nighttime turbulence profiling have been started and preliminary results will be shown. Methods for increasing adaptive optics system performance are being studied. Polarization modulation of the adaptive optics laser might be a method for laser guide star return flux enhancement. An experiment has been carried out at the Roque de la Muchachos Observatory on La Palma. As a byproduct of the experiment the Larmor frequency of mesospheric sodium was measured and the magnetic field strength in the mesosphere was determined. Adaptive optics system could benefit from an estimate of the mesospheric sodium density profile. Sodium density profiles can be retrieved by partial amplitude modulation with pseudo-random binary sequences of continuous-wave lasers. Results for an experiment at the Large Zenith Telescope in Maple Ridge and a feasibility study of this method for extremely-large telescopes will be presented. Event Location: Room 309, Hennings Bldg.
Event Time: Wednesday, June 19, 2019 | 12:30 pm - 2:30 pm
Event Location:
188 - Brimacombe 2355 E Mall, Vancouver, BC V6T 1Z4
Add to Calendar 2019-06-19T12:30:00 2019-06-19T14:30:00 Final PhD Oral Examination (Thesis Title: “Realizing High-Energy Physics in Topological Semimetals”) Event Information: Abstract: The discovery of topological phases of matter has brought high-energy and condensed matter communities together by giving us shared interests and challenges. One fruitful outcome is the broadened range of possibilities to realize high-energy physics in table-top experiments. My collaborators and I have found scenarios in which influential high-energy ideas emerge in solid-state systems built from topological semimetals – gapless topological phases which have drawn intense research efforts in recent years. This Thesis details our proposals for realizing Majorana fermions, Adler-Bell-Jackiw anomaly, and holographic black holes in superconductor-Weyl-semimetal heterostructures, mechanically strained Weyl semimetal nanowires/films, and graphene flakes subject to strong magnetic fields, respectively. By analyzing the effects of realistic experimental conditions, we will demonstrate that our proposals are experimentally tangible with existing technologies. Event Location: 188 - Brimacombe 2355 E Mall, Vancouver, BC V6T 1Z4
Event Time: Friday, June 7, 2019 | 12:00 pm - 2:00 pm
Event Location:
Room 309, Hennings Bldg
Add to Calendar 2019-06-07T12:00:00 2019-06-07T14:00:00 Departmental Oral Examination (Thesis Title: "Energy, Entropy and Spacetime: Lessons from Semiclassical Black Holes") Event Information: Thesis Abstract: This doctoral thesis explores semiclassical effects on black hole physics. Semiclassical theory refers as the application of quantum field theory in curved, classical background geometries, which respond to the expectation value of the regularised stress-energy tensor of the quantum matter. Among the original findings, I develop a few useful techniques to help regularising the stress-energy tensor in two dimensions; and their application to a model of stellar collapse to analyse the importance of quantum mechanical effects in the collapse itself. I found an explicit example showing that the behaviour of the late-times Hawking radiation does not depend on the details of the collapse and argued that any quantum mechanical effect is negligible for the collapse of an astrophysical object (whose mass is comparable to the solar mass). In the realm of black hole thermodynamics, I proved its first law for stationary black holes, proposed a definition for the entropy in piecewise stationary black holes which I showed to obey the generalised second law of thermodynamics. After also discussing its zeroth law, it becomes clear that this set of laws are originated in the semiclassical approach and it is made clear which hypothesis are necessary for these laws to hold. The derivation of these laws also point towards the long-standing question of the interpretation of the Bekenstein-Hawking entropy as accounting from the information perspective. Event Location: Room 309, Hennings Bldg
Event Time: Thursday, June 6, 2019 | 2:00 pm - 3:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-06-06T14:00:00 2019-06-06T15:30:00 CM Seminar: Kondo Blockade and Generative Hamiltonian Learning for molecular electronics Event Information: Abstract:  When nanoscale components are incorporated into external circuits, electronic transport can exhibit striking quantum phenomena with no classical analogue. Molecular junctions, in which a single molecule bridges the gap in a nanowire, constitute a particularly rich set of systems, demonstrating both strong correlation effects such as Coulomb blockade and Kondo, as well as quantum interference arising from orbital complexity. In this seminar, I discuss a general strategy for understanding the fundamental physics of such systems, which involves mapping complex microscopic models for the junction onto simpler generalized impurity problems that can be treated exactly. I highlight the limitations of the standard perturbative approaches, and introduce a new method for deriving effective models via machine learning techniques. The consequences for experimentally measurable quantum transport in molecular junctions are explored, including so-called "Kondo blockade". [1] Nature Communications, 8, 15210 (2017) Bio: Prof. Andrew Mitchell is a condensed matter theorist working on strongly correlated electron systems in the context of nanoelectronics, including quantum dot devices and molecular electronics. He obtained his PhD from Oxford University in 2010, and had postdoctoral fellowships at Cologne, Oxford, and Utrecht, before taking up a permanent position in theoretical physics at University College in Dublin, Ireland.   Event Location: BRIM 311
Event Time: Wednesday, June 5, 2019 | 3:00 pm - 4:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-06-05T15:00:00 2019-06-05T16:30:00 CM Seminar: From MEMS to Gravitational Wave Detectors: modeling energy dissipation in oxyde glasses at the atomic scale Event Information: Abstract: How are sound waves attenuated when they travel in a medium? How to damp most efficiently the vibrations due to an earthquake? Inversely, how to build a stable resonator? or avoid loosing energy when a laser beam rebounds on a mirror in a gravitational wave detector, the process which currently limits the precision of these very large interferometers. In order to answer these questions, we need to understand how mechanical energy is dissipated in materials. This process is complex and originates from distinct sources depending on the frequency of the deformation and the ratio between its wavelength and the characteristic length scales of the medium. The situation is particularly complex in disordered solids, which show a hierarchy of length scales. In this talk, we will discuss energy dissipation in oxide glasses and in particular silica, which is both a model glass and a technological glass used in many applications, including MEMS and optical coatings.  We will show how atomistic modeling can address both the very low (~ MHz) and very high (~ THz) frequency regimes, using different approaches. At low frequencies, dissipation is controlled by the thermally activated relaxation of local bi-stable regions, two-level systems, whose properties can be measured by sampling the potential energy landscape of the glass. By way of contrast, at high frequencies, the glass dynamics becomes harmonic and can be described using a normal mode analysis. We will see that in silica, which forms a tetrahedral network without coordination defects, dissipation and viscoelastic effects at both low and high frequencies are due to the vibration and reorientation of the Si-O-Si bonds between tetrahedra. Biography: David Rodney graduated from Ecole Paris Mines and University of Orsay. After a PhD at the Polytechnic Institute of Grenoble, he became a lecturer at SIMaP lab at INP Grenoble. From 2008 to 2009 he was a visiting professor at MIT in the department of "Material Science and Engineering". IUF junior in 2009, he joined the UCB Lyon 1 and ILM in teams Model ization of Condensed Matter and Interfaces and SOPRANO. Currently David works on the simulation of the mechanical properties of solids.   Event Location: BRIM 311
Event Time: Friday, May 17, 2019 | 2:00 pm - 3:30 pm
Event Location:
MACLEOD 418, 2335 Engineering Lane
Add to Calendar 2019-05-17T14:00:00 2019-05-17T15:30:00 CM Seminar: Vector beams, high harmonic generation and THz solenoidal magnetic fields Event Information: Abstract:  We use intense vector beams to generate high harmonics or to create solenoidal currents in solids or gases.  We create circularly polarized harmonics and we predict THz magnetic fields reaching the scale that is only available at user facilities. Event Location: MACLEOD 418, 2335 Engineering Lane