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HEP Seminars & Vivas

30 Sep 2023

UCL HEP Seminars 2023

Saad Shaikh PhD Viva (D17, Physics)

Examiners: Ryan Nichol (UCL), Tony Price (Birmingham)

: Maxwell Chertok (University of California, Davis)

The High Luminosity LHC CMS Outer Tracker Upgrade

The venerable CMS silicon strip tracker has detected charged particles emanating from high energy LHC proton-proton collisions at increasingly higher energies since its debut in 2008. Data from this detector played a major role in the Higgs boson discovery in 2012, and is centrally used in virtually every data analysis. Radiation damaged and with a data readout too slow for inclusion in the Level-1 trigger, the tracker will be replaced for the upcoming High Luminosity LHC (HL-LHC) era. In this talk, I present the HL-LHC Outer Tracker upgrade, a complete replacement for the strip tracker using state-of-the-art components, materials, and electronics. I will focus on OT detector mechanics and the status of the detector production.

: Suchita Kulkarni (University of Graz)

Exploring strongly interacting dark matter

Understanding the laws governing the dark matter dynamics in the Universe is undoubtedly one of the pressing questions inastro-particle physics. While investigations have focused on elementary particles as potential dark matter candidates, an equally interesting possibility arises if dark matter is a composite particle instead. I will take an overview of construction of such dark matter theories by extending the Standard Model with new non-Abelian sectors. I will further illustrate the benefits of connecting these constructions with lattice calculations. I will sketch the avenues of progress and highlight some of the open questions in this direction. Finally, I will exemplify the experimental signatures and impact of dark matter phenomenology.

: Thomas Teubner (Liverpool)

The puzzles of g-2: a status update

In this talk we will review the status of g-2 of the muon. The main emphasis will be on the Standard Model prediction and in particular the determination of the hadronic contributions which are the limiting factor. Recent developments, the current state of the discrepancy between experiment and theory as well as future prospects to resolve the puzzles will be discussed.

: Tomas Gonzalo (KIT)

Global studies of beyond the Standard Model theories: dark matter and supersymmetry

Beyond the Standard Model (BSM) theories aim to explain some of the missing ingredients of the Standard Model, yet no clear evidence for any of them has been found so far. Furthermore, most of these models introduce many new parameters, and make strong predictions for a multitude of experimental searches in particle physics, astrophysics and cosmology. Therefore, contrasting these theories with experimental data requires smart strategies to sample complicated parameter spaces and perform rigorous combinations of experimental results from many sources. In this talk I will introduce GAMBIT, a tool developed to make statistical studies of BSM theories easy and fast, and allow the study of models with many parameters and multiple experimen- tal searches. I will also show the results of various global studies of dark matter and supersymmetric models, where I will focus on their survival status in light of recent data and also on highlighting potential strategies to explore the remaining unconstrained parameter regions.

: Peter Bradshaw (UCL)

Uncovering the Secrets of Symmetries

Symmetries form a foundational part of the modern particle physics programme, from the interactions between particles to the very structure of the space-time they inhabit. We traditionally construct physical models out of representations of a given set of symmetries, associating collections of these representations with primitive physical objects such as the fields of elementary particles. The formalism of representation theory is well-developed and understood mathematically, and physicists have no trouble using them to extract phenomenological predictions. However, the physical interpretation of a representation is often not straightforward and sometimes requires additional notions outside the domain of the symmetry; this is also true when considering the similarities and differences between the physical properties of two different representations. In this talk, we will begin to overcome these difficulties and reveal the hidden physical structures within a representation. First, we will consider the usual approach to representation theory and motivate a new approach in terms of associative algebras. We will then consider an example of such methods applied to the symmetry governing non-relativistic spin and naturally entail the identification of physical properties beyond spin eigenstates. Finally, we will explore the potential that further studies of this kind may have for the myriad symmetries of particle physics

: Asli Abdullahi (Fermilab)

Exotic $e^+e^-$ production at MicroBooNE

We present a phenomenological study of MicroBooNE’s ability to investigate $e^+e^-$ final states produced in dark photon mediated neutrino-upscattering—a beyond-Standard Model process proposed as a solution to the MiniBooNE anomaly. Utilising the similarities shared between the observable signatures of neutrino-induced $e^+e^-$ and single photons originating in the radiative decays of the $\Delta(1232)$ resonance, we consider MicroBooNE’s recent public data from its search for neutral current $\Delta(1232)$ radiative decays to test benchmark models of $e^+e^-$ production, and investigate MicroBooNE’s sensitivity to heavy neutrino models in which the neutrino sector is strongly coupled to a dark sector.

: Sinead Farrington (Edinburgh)

Precision at the LHC

Precision at the LHC will continue to challenge theoretical calculations and tools. In this seminar I will discuss some of the LHC’s precision measurements in recent years, trends in them, and will shamelessly seek audience input to a workshop being organised later this year on the topic of legacy precision at the HL-LHC; what to work towards and how to achieve it.

: Sukanya Sinha (Manchester)

Not a jet all the way - an exploration of strongly interacting dark sector in ATLAS and beyond

As classic WIMP-based signatures for dark matter at the LHC have found no compelling evidence, several phenomenological studies have raised the possibility of accessing a strongly-interacting dark sector through new collider-event topologies. If dark hadrons exist, their evolution and hadronization procedure are currently little constrained. They could decay promptly and result in QCD-like jet structures, even though the original decaying particles are dark sector ones; they could behave as semi-visible jets (SVJ); or they could behave as completely detector-stable hadrons. ATLAS and CMS have recently come up with the first results, but this is only the beginning. In this talk, I will discuss the public results of the first t-channel ATLAS search for semi-visible jets, and the multiple pioneering studies we have performed on SVJ, covering three published or soon to be published papers. Finally, although not related to SVJ, I will cover our published work about an innovative search for dark photons in events with a top quark and a lepton jet

: David Yallup (Cambridge)

Evidence is all you need: Nested Sampling for particle physics

The Bayesian vs. Frequentist debate has raged for many years in particle physics, with the battle lines largely drawn and a set of established techniques falling firmly in favour of frequentist thinking. The same is largely true on the cosmology side of the fence, where the dominant paradigm is decidedly Bayesian. This is a curious fact that is worth considering, how have two adjacent fields that are so similar in ultimate goals and theoretical basis ended up at loggerheads when it comes to inference? To try and unravel some of this mystery, this talk will discuss the ‘Rosetta Stone’ of inference tasks in particle physics – searching for bumps in smoothly falling spectra at colliders. I will aim to extract the signal (the higgs) from the noise (the diphoton background), however in doing so I will really be attempting to extract the signal (why we use Nested Sampling so much in Cosmology) from the noise (the Bayesian vs. Frequentist debate). An “evidence based” approach (powered by Nested Sampling) affords unique perspectives on some long standing inference problems for High Energy Physics.

: Seb Jones (UCL)

The QTNM collaboration: a project for absolute neutrino mass measurement

The observation of neutrino oscillations provides proof of non-zero neutrino masses, something which was not predicted in the minimal Standard Model. However, these same neutrino oscillation experiments do not provide information on the absolute scale of the neutrino masses, which remain unknown. The neutrino masses are most directly accessed through those experiments which measure the shape of the beta-decay energy spectrum. In particular, a technique known as Cyclotron Radiation Emission Spectroscopy (CRES) offers the opportunity to measure neutrino masses lower than the current upper mass limit of 0.8 eV/c^2 achieved by the KATRIN collaboration. The Quantum Technologies for Neutrino Mass (QTNM) collaboration aims to utilise CRES, along with recent breakthroughs in quantum technologies, to build a demonstrator apparatus for measuring the neutrino mass. It is hoped that this demonstrator will make significant contributions towards an experiment with a neutrino mass sensitivity of O(10 meV). I will present an overview of the principles of neutrino mass measurement as well as the QTNM collaboration.

: Dieter Roehrich (Bergen)

Proton-CT - imaging with protons in particle therapy

A novel imaging modality using protons promises to overcome some limitations of particle therapy. Being able to position the Bragg peak accurately inside the tumor is a major advantage of charged particles, but incomplete knowledge about a crucial tissue property, the stopping power, limits its precision. A proton/helium-CT scanner provides direct information about the stopping power and has the potential to reduce range uncertainties significantly. A (clinical) prototype of a proton-CT has been designed and is being constructed in Bergen. The latest developments in Monolithic Active Pixel Sensors (MAPS) technology allow the fabrication of an extremely high granularity, large area silicon/absorber sandwich calorimeter with 41 sensitive layers of MAPS. A complete CT reconstruction of a simulated anthropomorphic paediatric head phantom shows that the concept of a single-sided detector setup and realistic pencil beam parameters gives a spatial uncertainty and a stopping power resolution sufficient for proton therapy treatment planning. The expected performance based on simulations, first beam test results and the status of the construction will be presented.