Seminars And Colloquia This Week

Accurate characterization of gravitational wave signals from binary black hole (BBH) mergers require efficient models for the waveform and remnant quantities. While we have accurate models for quasi-circular BBH mergers, modelling eccentric binaries is still in its nascent stage. Using both numerical relativity (NR) and black hole perturbation theory (BHPT), we study the phenomenology of eccentric BBH waveforms. We present convincing evidence that the waveform phenomenology in eccentric BBH mergers is significantly simpler than previously thought. We find that the eccentric modulations in the amplitudes and frequencies in different spherical harmonic modes are all related and can be modeled using a single time series modulation. Using this universal eccentric modulation, we provide a model named gwNRHME to seamlessly convert a multi-modal (i.e with several spherical harmonic modes) quasi-circular waveform into multi-modal eccentric waveform if the quadrupolar eccentric waveform is known. This reduces the modelling complexity of eccentric BBH mergers drastically as we now have to model only a single eccentric modulation time-series instead of modelling the effect of eccentricity in all modes. We use gwNRHME to include eccentricity in current NR surrogate waveform models for quasi-circular mergers. Additionally, we discuss efforts in building dedicated surrogate models for eccentric BBH mergers using both NR and BHPT.

In the first half of this talk, I present a search for new subatomic particles by looking for localized excesses in the dijet mass distribution of low-dijet-mass events produced in association with a high transverse momentum initial stated radiated photon. The search uses 140 fb$^{-1}$ of data collected by the ATLAS experiment between 2015 and 2018 at a center-of-mass energy of 13 TeV. Two variants are presented: one which makes no jet flavor requirements and one which requires both jets to be enriched in jets originating from b-quarks. In the absence of a statistically significant excess in the dijet invariant mass spectrum in either channel, limits were set on the production cross-section for a benchmark Z’ model and on generic beyond the Standard Model scenarios that produce Gaussian-shaped signals with a width of up to $15\%$ of the resonance mass in the dijet invariant mass spectrum. The analysis improves the sensitivity on the coupling of the Z’ to quarks by up to $50\%$ compared to previously published results. 

The future HL-LHC is expected to deliver an integrated luminosity of $3000$ fb$^{-1}$ during its operation, increasing the sensitivity to new physics that could elucidate the interaction between dark matter and matter or explain the underlying mechanism of electroweak symmetry breaking. The high instantaneous luminosity creates multiple proton-proton interactions per proton beam crossing that poses significant challenges for object and event reconstruction algorithms, particularly for tracking algorithms used in trigger selections. On online system known as the Event Filter implements a track reconstruction chain and reduces the data rate from 40 MHz to 10kHz. I present a new method for data preparation as part of track reconstruction and a novel application of the pattern recognition on FPGAs used in the online trigger to efficiently identify track candidates within the future ATLAS Inner Tracker. This algorithm is found to significantly reduce the number of fake candidates found, making the process of track fitting less computationally intensive. 

NOνA is a long-baseline neutrino oscillation experiment with two highly segmented liquid-scintillator detectors: a near detector at Fermilab and a much larger far detector in Ash River, Minnesota. The far detector is at the surface with little overburden.  It has been running with nearly continuous livetime since 2014.  The enormous surface area of 4200 m² of the far detector and its surface location make it ideal for sensitive searches for intermediate- to high-mass magnetic monopoles 10⁶-10¹⁸ GeV, as well as other exotic highly ionizing, subliminal particles. This search implements a unique data-driven trigger.  We describe how the enormous cosmic-ray muon rate is defeated to allow a background-free search to be obtained and compare our sensitivity to previous results.

The transition of many materials of interest for the condensed matter community, particularly in energy-related applications, from crystalline materials to heterostructures and complex architectures, where different compounds are combined, stacked, interfaced and twisted in different ways, has forced the experimental techniques to evolve accordingly. Angle-resolved photoemission (ARPES), which has been for decades a spectroscopy of reference for accessing the low energy excitations in solids, had to implement a number of updates to keep pace with the progress made in materials fabrication. This talk will discuss some of the latest trends in ARPES, how it has advanced and to where it is moving in order to remain an invaluable tool for studying the electronic properties of materials.

The pyramids of ancient Egypt and of pre-Hispanic Mesoamerica have fascinated people since the cultures that built them vanished into the annals of history.  How were they built?  What were they used for?  Are there unknown internal substructures, perhaps hidden chambers that have yet to be discovered?  Using the detector technology we developed for a particle physics experiment at Fermilab, we intend to perform non-invasive searches for hidden structures at the Great Pyramid of Khufu, in Egypt, and at the Temple of Kukulkán at Chichén Itzá.  The apparatus will detect cosmic-ray muons produced high in the atmosphere that course through the pyramids to produce a tomographic image of their interiors. I will review the status of both projects, describe in detail the technique we intend to use, present recent simulation results and detector prototype results.