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HEP Seminars

04 Feb 2023

UCL HEP Seminars 2022

: Matthew Mccullough (CERN)

The Higgs Boson Under a Microscope

What does the Higgs boson look like if you put it under a microscope? How does it move? Is it made up of smaller parts? Does it give itself mass? In this talk I will sketch a theoretical range of possible answers to these questions and, ultimately, how we might hope to answer them with the HL-LHC and future colliders.

: Giacomo Magni (Nikhef)

Evidence for intrinsic charm quarks in the proton

QCD, describes the proton in terms of quarks and gluons. The proton is a state of two up quarks and one down quark bound by gluons, but quantum theory predicts that in addition there is an infinite number of quark-antiquark pairs. Both light and heavy quarks, whose mass is respectively smaller or bigger than the mass of the proton, are revealed inside the proton in high-energy collisions. However, it is unclear whether heavy quarks also exist as a part of the proton wavefunction, which is determined by non-perturbative dynamics and accordingly unknown: so-called intrinsic heavy quarks. After a brief introduction how parton distribution functions (PDFs) can be extracted from high energy data, we provide a first evidence for intrinsic charm by exploiting a high-precision determination of the quark-gluon content of the nucleon based on machine learning and a large experimental dataset. We disentangle the intrinsic charm component from charm-anticharm pairs arising from high-energy radiation, showing a generally good agreement with models. Finally we show how these findings can be compared to recent data on Z-boson production with charm jets from the LHCb experiment.

: Andrew Stevens (UCL)

First results from LUX-ZEPLIN

The LUX-ZEPLIN (LZ) experiment is a dark matter detector centred on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. Results from LZ's first search for Weakly Interacting Massive Particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5 tonnes were recently published. A profile-likelihood analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon cross-sections for WIMP masses above 9 GeV/c2 . The most stringent limit is set at 30 GeV/c2 , excluding cross sections above 5.9 × 10−48 cm2 at the 90% confidence level. This talk will give an overview of the LZ detector, a description of the first results, and a brief look at the science program that is now accessible with the LZ experiment.

: Lydia Beresford (DESY)

Measuring tau g-2 using Pb+Pb collisions

The electromagnetic moments of the tau lepton are highly sensitive to new physics but are challenging to measure due to the short tau lifetime. Recently, the ATLAS and CMS Collaborations set the first new constraints on the tau magnetic moment (‘g-2’) in nearly two decades, using LHC heavy ion collisions as an intense source of photon collisions to observe photo-production of tau pairs in Pb+Pb collisions. In this seminar I will discuss these new results and I will also highlight exciting future prospects.

: Sonia Escribano Rodriguez (UCL)

Prompt gamma-ray imaging of nanoparticles for in vivo range verification in proton therapy

Proton therapy is an emerging modality for cancer treatment. It produces a better dose conformation, reducing the damage to the surrounding healthy structures and tissues. However, in vivo range verification is desirable to minimize beam delivery errors during the treatment. The most promising range verification technique is prompt gamma-ray imaging (PGI). In addition, the use of nanoparticles (NPs) in proton therapy has been developed in the past years, as particles with high atomic number produce an enhancement in the dose received by the tumor. The aim of the project is to investigate the feasibility of performing prompt gamma-ray imaging measurements using characteristic gamma rays emitted from a nanoparticles target. To test the proof of principle an in-house designed target, consisting of a solution of magnetite NPs (Fe3O4) diluted in water, was irradiated with a proton beam at different energies. Two different detection systems were placed perpendicular to the target to measure the prompt gamma-rays emitted from the NPs after the proton irradiation. The experimental results, obtained at KVI-CART and the University of Birmingham, are compared to a Geant4 Monte Carlo simulation.

: Rafael Teixeira De Lima (SLAC)

Exploring Di-Higgs production with beauty quarks and Machine Learning

The Standard Model of particle physics dictates how our universe works. Decades of experimental research have probed it in details. In the last 10 years, the final piece of the puzzle, the Higgs boson, has been discovered and studied to great precision. However, one area of the Standard Model remains a mystery: the Higgs potential. Determining the parameters of the Higgs potential can have significant implications in the nature of the electroweak symmetry breaking (the process by which fundamental particles acquire mass) and the history of the universe. In this talk, I will explore how we study the Higgs potential at the Large Hadron Collider (LHC) through the search for events where two Higgs bosons are produced (Di-Higgs). In particular, I will describe how the ATLAS experiment at the LHC conducts this search via the Higgs decays to beauty quarks. This search is only possible through the use of different Machine Learning algorithms, which will also be discussed.

: Kevin Lesko (LBL)

Low Background Assay & Cleanliness Requirements for Future Rare-Search Experiments

I will review low background assay for fixed contaminants and surface cleanliness efforts from SNO, LUX, and LZ. Future large-scale rare-search experiments such as a G3 LXe or Neutrinoless Double-beta Decay may benefit from these experiences and lessons-learned. The challenges of large scale, underground construction efforts, and increasingly lower acceptable levels of fixed contamination are examined.

: Robin G. Stuart

Searching For Shackleton’s Vessel Endurance – in the numbers

On 21 November 1915 Sir Ernest Shackleton’s vessel Endurance was crushed by ice in the Weddell Sea and sank at a position given as 68°39¢30²S 52°26¢30²W. Close examination of the sextant sights recorded in Captain Frank Worsley’s original logbooks showed, however, that the location of the wreck would be offset from this position. The navigational methods and calculations that Worsley used to fix the position will be discussed as well as the reanalysis of the observations using modern techniques. Lunar occultation timings, performed in the southern winter of 1915 to rate the chronometers for longitude, were reduced using JPL ephemerides for the Moon and Hipparcos star positions and yield results that are significantly different from those obtained from tables in the Nautical Almanac of the time. Various factors are at play but when taken together they predicted that the wreck should lie to the south and likely to the east of the recorded position.

: Chris Hays (Oxford)

High-precision measurement of the W boson mass with the CDF II detector

The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After the observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 TeV centre-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. The measured value is in tension with the prediction of the model.

: Louie Corpe (CERN)

The search for exotic long-lived particles: illuminating a blind spot of the LHC programme

Exotic long-lived particles (LLPs) occur in many well-motivated extensions to the Standard Model (SM) of particle physics, and could explain the nature of Dark Matter (DM). However, LLPs could have been missed by the traditional LHC search programme to date due to their non-standard energy deposition patterns, which would often be thrown away as noise by standard reconstruction techniques. LLP signatures could be hiding in the “Blind Spot” of LHC searches! This talk will include a general motivation for LLP searches, and highlight the sort of signatures which are expected at CMS and ATLAS, as well as the unusual background which must be mastered. Recent examples of LLP results from the ATLAS collaboration will be used to highlight some of the novel techniques which are employed in these searches. Finally, prospects for the development of the LLP programme at CERN in coming years will be presented.

: IoP Practice Talks — E7/Zoom

IoP Practice Talks

Practice Talks for IoP Conference.

: Sean Mee (Graz)

On the construction of theories of composite dark matter

The dark matter remains one of the most famous unanswered questions in physics today. Despite the popular weakly interacting massive particle (WIMP) paradigm, a new class of theories posits that dark matter could be described as the lightest bound state in a QCD-like confining hidden sector. We discuss the construction of theories which describe the interactions of these states with other interesting bound states of the hidden sector, with a particular focus on pseudoreal symmetry groups. We highlight the key differences between such theories and the more familiar SM QCD. We present some results for the low-energy quantities describing the spectrum of these composite theories (masses and decay constants). Finally, we discuss the simplest portals which could allow us to look for such sectors at colliders and elsewhere, the associated symmetry breaking patterns and the potential phenomenological consequences.

: Prof. David Waters — Harrie Massey LT

XXXI Elizabeth Spreadbury Lecture: The Mystery of Neutrino Mass

We don't know the mass of the most abundant fermion in the universe. We suspect that the origin of neutrino masses might be quite different from those of other fundamental particles. The talk will begin with a review of what we know about neutrino mass and its generation. We will present experiments, some of which are UCL-led, that aim to determine the nature of neutrino mass. A crude neutrino mass measurement will be attempted during the lecture itself, before presenting a perspective on how this field may develop over the next few years.

: Nicola McConkey (Manchester)

Latest results from MicroBooNE and the outlook for the SBN programme

The MicroBooNE experiment is a liquid argon neutrino detector making groundbreaking neutrino physics measurements in the BNB and NuMI beamlines at Fermilab. I will present the latest results from new physics searches and neutrino cross-section measurements with MicroBooNE, and the outlook for the future, with a particular view to the physics potential of the Short Baseline Neutrino programme at Fermilab.

: Inwook Kim (LANL)

Results from Baksan Experiment on Sterile Transitions (BEST)

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos, ƞe, observed in previous gallium-based radiochemical measurements with high intensity neutrino sources, commonly referred to as the gallium anomaly. Based on the Gallium-Germanium Neutrino Telescope (GGNT) of the SAGE experiment, the BEST setup is comprised of two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Any deficits in the 71Ge production rates in the two zones, as well as the differences between them, would be an indication of nonstandard neutrino properties at this short scale. From July 5th to October 23rd 2019, the two-zone target was exposed to the mainly monoenergetic 51Cr neutrino source ten times with 20 independent 71Ge extractions from the two Ga targets. The 71Ge decay rates were measured from July 2019 to March 2020 to determine the total production rate from the neutrino source. At the end of the experiment, the counting systems were calibrated using 71Ge isotope data taken in November 2020. We report the results from the BEST sterile neutrino oscillation experiment. 4σ deviations from unity were observed for the ratio of the measured 71Ge production rate to the predicted rate from the known cross section in both zones and confirm the previously reported Ga anomaly. If interpreted in the context of neutrino oscillations, the deficits give best fit oscillation parameters of Δm2 = 3.3+∞-2.3 ~eV2 and sin2 2θ = 0.42+0.15-0.17, consistent with νe → νs oscillations governed by a surprisingly large mixing angle.

: Veronique Boisvert (RHUL)

The Climate Emergency: can Particle Physics ever be sustainable?

We live in a climate emergency and consequently all countries are putting in place measures to reduce their carbon emissions in order to reach a so-called “net zero emissions” by 2050. All aspects of economic life will be affected by such measures, including particle physics research. I will present some examples of sources of carbon emissions within the field of particle physics. This will include emissions associated with building and running accelerators, detector operations, high-performance computing and activities associated with our research life like travel. I will also present solutions being developed for addressing this in the near and long term as well as recommendations for the field.

: Alexander Booth (Queen Mary)

Latest 3-flavour Oscillation Results form the NOvA Experiment

NOvA is a long-baseline neutrino oscillation experiment searching for electron neutrino appearance and muon neutrino disappearance. To do this, NOvA uses the NuMI beam at Fermi National Accelerator Laboratory along with two functionally identical detectors, separated by a baseline of 809 km. A near detector, which is close to the point of neutrino production, provides a measurement of initial beam energy spectra and flavour composition. The spectra are then extrapolated to a far detector and compared to data to look for oscillations. The experiment is able to constrain several parameters of the PMNS matrix and is sensitive to the neutrino mass hierarchy. This seminar presents a 3 flavour oscillation analysis of 6 years of NuMI data collected by the NOvA far detector corresponding to a 14 ktonne equivalent exposure of 3.60\times 10^{20}$ and 2.50\times 10^{20}$ protons on target, in neutrino and antineutrino beam modes respectively. The analysis, shown for the first time at the International Conference on Neutrino Physics and Astrophysics in 2020, builds on previous results with a new simulation, updated reconstruction and roughly 50\% more neutrino data.

: Sunny Vagnozzi (Cambridge)

Terrestrial, cosmological, and astrophysical direct detection of dark energy

Most of the efforts in searching for dark energy, the component responsible for the accelerated expansion of the Universe, have focused on its gravitational signatures and in particular on constraining its equation of state: however, there is a lot to be learned about dark energy by getting off the beaten track. I will argue that non-gravitational interactions of dark energy with visible matter are natural and somewhat unavoidable, and lead to the possibility of direct