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HEP Seminars

01 Jun 2020

UCL HEP Seminars 2018

14-12-2018 : Alexander Deisting (RHUL)

Taking a Time Projection Chamber to high pressure

Time Projection Chambers (TPCs) have been employed with great success as tracking detectors and to provide particle ID, since they provide a large active volume and low momentum threshold for particle detection. We currently develop a high pressure TPC (HPTPC) which can operate at gas pressures of up to 5 barA. Increasing the pressure allows to increase the target mass inside the active volume, thus making a HPTPC a promising candidates to characterise neutrino beams at the next generation long baseline neutrino oscillation experiments such as DUNE or Hyper-K. Our HPTPC prototype features a gas amplification stage with three parallel meshes, charge readout at each mesh and an optical readout with four CCD cameras. The talk will focus on the hardware of the detector, its operation and the according challenges as well as some measured results. Possible future developments will be discussed as well.


07-12-2018 : Loredana Gastaldo (Heidelberg)

Metallic Magnetic Calorimeters for Neutrino Physics

The wish to understand properties of neutrinos has been driving very challenging experiments since the discovery of these elusive particles. In the early ’80, the development of low temperature detectors, operated at millikelvin temperatures, was strongly motivated by the possibility to enhance our knowledge on neutrino Physics. Even today, in the landscape of experiments investigating neutrino properties, low temperature detectors are still playing a very important role. This talk will describe the use of a particular type of low temperature detectors, metallic magnetic micro-calorimeters in experiments for the determination of the electron neutrino mass and for the search of neutrinoless double beta decay. Finally we will discuss other applications as search for keV sterile neutrinos or measurements of coherent neutrino nucleus scattering in which metallic magnetic micro-calorimeters could play a very important role.


30-11-2018 : Chris Stoughton (Fermilab)

Muon g-2 and other news

After 50 years of operation, Fermilab is still going strong. I will discuss the motivation, status, and prospects of the FNAL g-2 experiment. I'll place it in historical context, especially regarding Fermilab's future programs. I will end with a brief explanation of Fermilab's "smallest" experiment, the Holometer, which measures effect of Planck-scale physics.


16-11-2018 : Andi Chisholm (Birmingham)

Searching for Higgs boson decays to charm quark pairs with charm jet tagging at ATLAS

The Standard Model (SM) Higgs boson is expected to decay to a charm quark pair in around 3% of cases. While this number seems small, the success of the LHC Higgs boson measurement programme is such that this contribution represents one of the largest expected contributions to the total Higgs boson decay width for which we have no experimental evidence. Furthermore, all experimental evidence for Yukawa couplings is limited to the third generation fermions and the smallness of the SM charm quark Yukawa coupling makes it particularly sensitive to modifications from potential physics beyond the SM. I will describe a novel charm jet tagging algorithm recently commissioned by the ATLAS experiment and discuss how it can be employed to perform the first direct search for Higgs boson decays to charm quark pairs with the ATLAS experiment (Phys. Rev. Lett. 120 (2018) 211802, arXiv:1802.04329). Looking beyond this LHC Run 2 result, the prospects and projected sensitivity for this channel at the HL-LHC will also be discussed.


09-11-2018 : Jeanne Wilson (QMUL)

SNO+: Current Status and Prospects

The SNO+ experiment is a multi-purpose low energy neutrino experiment based in the SNOLAB deep underground facility in Canada. The experiment builds on the infrastructure of the successful SNO experiment, with liquid scintillator replacing the original heavy water detection medium. The main goal of SNO+ is to search for neutrino-less double beta decay of tellurium-130, which will be dissolved in the liquid scintillator. If observed, neutrino-less double beta decay would confirm the Majorana nature of neutrinos and provide information on absolute neutrino mass. Additionally, SNO+ plans to make measurements of reactor neutrinos, geo-neutrinos, solar neutrinos and will be sensitive to neutrinos from galactic supernovae. For the past year, SNO+ detector commissioning has involved collecting data with H2O as a detection medium, allowing observation of solar neutrinos with extremely low background and a search for invisible modes of nucleon decay, which will be presented in this talk.


02-11-2018 : Ioana Maris (ULB)

Current status and future of Ultra High Energy Cosmic Rays experiments

The Earth's atmosphere is constantly bombarded by ultra high energy cosmic rays (UHECRs). These particles carry the largest energies known to us: they can reach more than 10²⁰ eV. Their flux is very low, and thus very large detectors were built to be able to detect the secondary particles produced by UHECRs after entering the atmosphere. I will present the results of the forerunner experiments, Pierre Auger Observatory and Telescope Array, regarding the energy spectrum, mass composition and arrival directions. Even though a large progress has been made in the last 10 years, we still do not know where these particles are coming from. In the last part of this talk I will present the future plans to advance in the quest of the origin of UHECRs.


26-10-2018 : Eram Rizvi (QMUL)

Precision EW Measurements from ATLAS - sin^2\theta_eff

The phenomenal operation of the LHC in Run-1 has allowed high precision measurements to be attained for single vector boson production in pp collisions. A new measurement of the cross section for Z\gamma production at \sqrt{s}=8 TeV will be presented triple differentially in dilepton invariant mass, |y| and \cos\theta covering the region 46$<$m$<$200 GeV; 0$<|y|<$3.6; and -1$<$cos\theta$<$+1. The measurement is designed to be simultaneously sensitive to the proton PDFs and to the weak mixing angle. A precision of better than 0.5% in the region m ~ mZ (excluding luminosity uncertainty) is achieved. The value of sin^2\theta_eff is extracted using this cross section data, and also using the approach of scattering amplitude coefficients. An accuracy of ±36 x 10^{-5} is achieved reaching the combined CDF+D0 accuracy and approaching the LEP and SLD results.


19-10-2018 : Physics Gala

No seminar this week



12-10-2018 : Christoph Andreas Ternes (IFIC Valencia)

Status of 3-neutrino oscillations

In this talk I will present the current status of neutrino mixing angles and masses. I will explain how simulations are performed and give a brief introduction to the theory of neutrino oscillations. Afterwards I will discuss all the experiments included in the global fit, before going to the results of the combined analysis. There I will focus on the currently open problems, such as atmospheric octant, CP-violation and neutrino mass ordering.


14-06-2018 : Teppei Katori (QMUL)

Observation of a Significant Excess of Electron-Like Events in the MiniBooNE Short-Baseline Neutrino Experiment

The MiniBooNE experiment at Fermilab reports results from an analysis of electron neutrino (nue) appearance data from 1.3E21 protons on target (POT) in neutrino mode, an increase of approximately a factor of two over previously reported results (PRL110(2013)161801). A nue charged-current quasi-elastic (CCQE) event excess of 381.2 +/- 85.2 events (4.5sigma) is observed in the energy range 200 < EnuQE < 1250 MeV. Combining these data with the electron anti-neutrino (nuebar) appearance data from 1.1E21 POT in antineutrino mode, a total nue plus nuebar CCQE event excess of 460.5 +/- 95.8 events (4.8 sigma) is observed. If interpreted in a standard two-neutrino oscillation model (numu to nue), the best oscillation fit to the excess has a probability of 20.1% while the background-only fit has a chi2-probability of 5E-7 relative to the best fit. The MiniBooNE data are consistent in energy and magnitude with the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND), and the signicance of the combined LSND and MiniBooNE excesses is 6.1 sigma. All of the major backgrounds are constrained by in-situ event measurements, so non-oscillation explanations would need to invoke new anomalous background processes. Although the data are fit with a standard oscillation model, other models may provide better fits to the data. https://arxiv.org/abs/1805.12028


01-06-2018 : Justin Evans (Manchester)

A combined view of sterile-neutrino constraints from CMB and neutrino-oscillation measurements.

I will present a comparative analysis of constraints on sterile neutrinos from the Planck experiment and from current and future neutrino-oscilllation experiments, as reported in S. Bridle et al., Phys. Lett. B764, 322 (2017). In this paper, we, for the first time, expressed joint constraints on N_eff and m_eff^sterile from the CMB in the Δm^2, sin^2(2θ) parameter space used by oscillation experiments, and expressed constraints from oscillation experiments in the N_eff, m_eff^sterile cosmology parameter space. We focused on oscillation experiments that probed mixing of the muon flavour into a fourth mass state: MINOS, IceCube, and the SBN programme. I will then present new work in which we have looked at mixing of the electron flavour to allow comparison of CMB constraints with limits from the reactor experiments NEOS and Daya Bay. Finally, we allow both the electron and muon flavours to simultaneously mix with a fourth mass state, and compare CMB constraints to the numubar->nuebar appearance signals from LSND and MiniBooNE.


18-05-2018 : Anne Norrick (William&Mary)

Recent and upcoming Results from the MINERvA Experiment

The MINERvA experiment is a dedicated neutrino cross section experiment stationed in the Neutrinos from the Main Injector (NuMI) beam line at Fermi National Accelerator Laboratory in Batavia, IL, USA. Recent results from the MINERvA experiment, as well as upcoming results using a beam of increased energy and intensity and their impact on the field will be discussed.


11-05-2018 : Jim Dobson (UCL)

Searching for dark matter with the LUX and LUX-ZEPLIN direct detection experiments

For the past decade liquid xenon time-projection chambers (TPCs) hidden deep underground have led the race to make a first direct detection of dark matter here on Earth. In this talk I’ll present the final results from the recently completed Large Underground Xenon (LUX) experiment as well as the status and physics reach of its successor, the 40 times as massive LUX-ZEPLIN experiment currently being constructed and due to start data taking in 2020.


04-05-2018 : Giuliana Galati (Naples)

Final results of the OPERA experiment on tau neutrino appearance in the CNGS beam

The OPERA experiment (Oscillation Project with Emulsion tRacking Apparatus) was designed to conclusively prove the muon neutrino into tau neutrino oscillation in appearance mode. In this talk the improved and final analysis of the full data sample, collected between 2008 and 2012, will be shown. The new analysis is based on a multivariate approach for event identification, fully exploiting the expected features of tau neutrino events, rather than on the sheer selection of candidate events by independent cuts on topological or kinematical parameters as in previous analyses. It is performed on candidate events preselected with looser cuts than those applied in the previous cut-based approach. Looser cuts increase the number of tau neutrino candidates, thus leading to a measurement of the oscillation parameters and of the tau neutrino properties with a reduced statistical uncertainty. For the first time ever, Delta m^2_{23} has been measured in appearance mode, tau neutrino CC cross-section has been measured with a negligible contamination from τ antineutrinos and tau neutrino lepton number has been observed. Moreover, given the higher discrimination power of the multivariate analysis, the significance of the tau neutrino appearance is increased.


27-04-2018 : Michela Massimi (Edinburgh)

Perspectival modeling at LHC

The goal of this paper is to address the philosophical problem of inconsistent models, and the challenge it poses for realism and perspectivism in philosophy of science. I analyse the argument, draw attention to some hidden premises behind it, and deflate them. Then I introduce the notion of “perspectival models” as a distinctive class of modeling practices, whose primary function is heuristic or exploratory. I illustrate perspectival modeling with two examples taken from contemporary high-energy physics at LHC, CERN (one from ATLAS concerning pMSSM-19 and one from the CMS experiment). These examples are designed to show how a plurality of seemingly incompatible models (once suitably understood) is in fact methodologically very important for scientific progress and for advancing knowledge in cutting-edge areas of scientific inquiry.


13-04-2018 : Stephen West (RHUL)

Dark Matter models

I will start by reviewing a range of non-standard dark matter models including models employing asymmetric dark matter and freeze-in. I will then go on to outline models of Nuclear Dark Matter, where the dark matter states are composite objects consisting of ``dark nucleons”. I will outline some of the novel features of this idea and how the composite nature can lead to interesting signatures in direct detection experiments.


06-04-2018 : Tuomas Rajala (UCL)

Detecting local scale interactions in highly multivariate point patterns

Highly multivariate point patterns, such as the location patterns of 300 different plant species in a rainforest, are the big data of point pattern statistics. One of the main data analysis goals is the detection of local scale interactions between different point types/species. This talk will discuss two approaches for detecting such interactions: A Monte Carlo framework based on pairwise non-parametric tests, and a multivariate Gibbs model technique relying on automatic variable selection.


22-03-2018 : Tianlu Yuan (UW-Madison)

IceCube: a nu-window into the Universe

The IceCube Neutrino Observatory, a cubic-kilometer in-ice detector at the South Pole, offers a unique window into the smallest and largest scales of our universe. Over the past several years, IceCube has detected the first high-energy neutrinos of astrophysical origin, measured atmospheric neutrino oscillations, and performed searches of neutrino sources throughout the sky. As more data is collected, a reduction of systematic uncertainties becomes ever more important for neutrino astronomy and neutrino property measurements in IceCube. These two paths are connected as, at the highest energies, the angular resolution of events without an observable muon is limited primarily by ice-property uncertainties. To pave the road forward, in this talk I will explore improvements to event reconstruction and systematic treatment in the high-energy starting event (HESE) analysis. I will discuss a new high-energy cross-section measurement using the HESE sample and a novel calculation of the atmospheric neutrino background. I will conclude with an outlook for the future with IceCube-Gen2.


16-03-2018 : Seth Zenz (Imperial)

Understanding the Higgs Boson: Where We Are, Where We're Going, and How To Get There

In 2012, the ATLAS and CMS experiments at the CERN Large Hadron Collider discovered a new particle. With analysis of data through 2016 now largely completed, we know more precisely than ever that this particle is highly consistent with the Standard Model (SM) Higgs boson. But is the SM realized exactly, or do some differences in the Higgs boson's properties provide a window into new physics? During the 2020's and 2030's, the High Luminosity LHC will supply a large enough dataset to answer this question with very precise and fine grained measurements. I will outline the current understanding of the Higgs boson, the plans for long-term studies at the LHC, and the measurements we can make now to build up our knowledge in the medium-term and prepare better for the long program ahead.


09-03-2018 : Kate Pachal (SFU)

Searches for new low-mass resonances in jetty events at ATLAS

"Searches for beyond-standard-model particles in dijet invariant masses have been a been a key feature of physics programs across 30 years of collider experiments. As no new particles at high masses have yet been discovered, some analyses have moved from pushing this final state towards higher and higher scales in favour of searching for small cross section or small branching ratio signals at lower masses. This is ideal for searching for dark matter mediator candidates, where the dijet channel can be a powerful constraint. Low masses pose a serious challenge for searches in fully hadronic final states because of the trigger prescales which make dataset accumulation difficult in this regime. Two ways around this constraint have been explored in Run II: first, the analysis can be performed with minimal event information at the level of the trigger. This poses a lot of unique technical challenges because of the need for a custom jet calibration. Second, the analysis can search for dijet resonances produced in association with an object which can be used for triggering: a higher-pT jet or a photon. This seminar will discuss the most recent public results for both analysis methods."


POSTPONED!!! 02-03-2018 : Kate Pachal (SFU)

POSTPONED!!! Searches for new low-mass resonances in jetty events at ATLAS

"Searches for beyond-standard-model particles in dijet invariant masses have been a been a key feature of physics programs across 30 years of collider experiments. As no new particles at high masses have yet been discovered, some analyses have moved from pushing this final state towards higher and higher scales in favour of searching for small cross section or small branching ratio signals at lower masses. This is ideal for searching for dark matter mediator candidates, where the dijet channel can be a powerful constraint. Low masses pose a serious challenge for searches in fully hadronic final states because of the trigger prescales which make dataset accumulation difficult in this regime. Two ways around this constraint have been explored in Run II: first, the analysis can be performed with minimal event information at the level of the trigger. This poses a lot of unique technical challenges because of the need for a custom jet calibration. Second, the analysis can search for dijet resonances produced in association with an object which can be used for triggering: a higher-pT jet or a photon. This seminar will discuss the most recent public results for both analysis methods."


23-02-2018 : Francesco Coradeschi (Cambridge)

Precision physic at colliders: introducing reSolve, a transverse momentum resummation tool

Since the early days of the Large Hadron Collider (LHC), a large part of the experimental effort was focused on direct searches for signals of New Physics. It is however important (and increasingly so, given the absence of any direct detection so far) to also explore alternative strategies, and foremost among these is precision physics. Traditionally, hadron machines such as the LHC were not considered particularly well-suited to precision studies, but experimental collaborations at CERN have already provided us with excellent measurements which exceed our best theoretical predictions precision-wise, and can only be expected to get better as the LHC continues its run. It is crucial for the theoretical community to keep up with this trend, especially considering that most realistic, still viable, extensions of the Standard Model (SM) are compatible with only small deviations from SM predictions, at LHC energies, for arbitrary observables. The transverse momentum spectrum is a particularly interesting observable for the precision program: in general processes, a majority of events is produced at relatively soft transverse momentum scales, and the physical behaviour at these soft scales is an highly nontrival prediction of perturbative QCD (and thus of the SM) which requires a resummation of logarithmically-enhanced contributions to all orders in the strong coupling \alpha_s. In this talk, I will introduce the new tool reSolve, a Monte Carlo differential cross-section and parton-level event generator whose main new feature is to add transverse momentum resummation to a general class of inclusive processes at hadron colliders. reSolve uses the impact parameter formalism, which is particularly well-suited to general studies. During the talk I will briefly review transverse momentum resummation in general, the peculiarities of its implementation in reSolve, and conclude commenting some of the possible phenomenological applications and future developments.


16-02-2018 : Nassim Bozorgnia (Durham)

The dark halo of Milky Way-like galaxies

One of the major sources of uncertainty in the interpretation of dark matter direct and indirect detection data is due to the unknown astrophysical distribution of dark matter in the halo of our Galaxy. Realistic numerical simulations of galaxy formation including baryons have recently become possible, and provide important information on the properties of the dark matter halo. I will discuss the dark matter density and velocity distribution of Milky Way-like galaxies obtained from high resolution hydrodynamical simulations. To make reliable predictions for direct and indirect detection searches, we identify simulated galaxies which satisfy the Milky Way observational constraints. Using the dark matter distribution extracted from the selected Milky Way-like galaxies, I will present an analysis of current direct detection data, and discuss the implications for the dark matter interpretation of the Fermi GeV excess.


09-02-2018 : Stefan Guindon (CERN)

Recent ATLAS Results in the search for ttH production

The observation of the production of ttH is an important test of the top Yukawa coupling of the Higgs boson, and one of the main goals of Run-2 of the Large Hadron Collider. It remains one of the most important characteristics of the Higgs boson which has yet to be directly observed. Many models of new physics beyond the Standard Model predict significant deviations of this coupling, which would be directly observable via the measurement of ttH production. The new ATLAS searches for ttH associated production at centre-of-mass energies of 13 TeV will be presented. The search targets several Higgs boson decays, including final states with multiple b-quarks, multileptons, and two photons.


02-02-2018 : Yiannis Andreopoulos (UCL)

Deep Learning from Compressed Spatio-Temporal Representations of Data

Deep learning has allowed for (and incentivised) researchers to look at data volumes and processing tasks that have previously only been hypothesized. While the first-generation of deep supervised learning achieved significant advances over shallow learning methods, it is increasingly becoming obvious that many approaches were naive in their design and we are only scratching the surface of what is possible. The notion of strong supervision (i.e., the use of labels during training) is impractical and easy to fool by adversarial examples and, perhaps most importantly, operating with uncompressed samples (e.g., input image pixels of video or audio) does not scale. For instance, data generated from visual sensing in Internet-of-Things (IoT) application contexts will occupy more than 82% of all IP traffic by 2021, with one million minutes of video crossing the network every second [Cisco VNI Report, Jun. 2017]. This fact, in conjunction with the rapidly-increasing video resolutions and video format inflation (from standard to super-high definition, 3D, multiview, etc.), makes the scale-up of deep learning towards big video datasets unsustainable. To address this issue, we propose to go beyond the pixel representations and design advanced deep learning architectures for classification and retrieval systems that directly ingest compressed spatio-temporal activity bitstreams produced by: (i) mainstream video coders and (ii) neuromorphic vision sensing cameras. By exploiting the compressed nature of our inputs, our approach can deliver 100-fold increase in processing speed with comparable classification or retrieval accuracy to state-of-the-art pixel-domain systems and has the potential to be extended to self-supervised deep learning. The talk will explain the key steps of our approach and can motivate researchers to think carefully about the sensing and supervision modalities of their problems prior to embarking on the use of deep learning tools for data analysis. Related paper: https://arxiv.org/abs/1710.05112


26-01-2018 : Jonathan Davis (Kings)

CNO Neutrino Grand Prix: The race to solve the solar metallicity problem

Several next-generation experiments aim to make the first measurement of the neutrino flux from the Carbon-Nitrogen-Oxygen (CNO) solar fusion cycle. This will provide crucial new information for models of the Sun, which currently are not able to consistently explain both helioseismology data and the abundance of metal elements, such as carbon, in the solar photosphere. The solution to this solar metallicity problem may involve new models of solar diffusion or even the capture of light dark matter by the Sun. I look at how soon electronic-recoil experiments such as SNO+, Borexino and Argo will measure the CNO neutrino flux, and the challenges this involves. I also consider experiments looking for nuclear-recoils from CNO neutrinos, which requires sensitivity to very low energies, and discuss how the same technology is also key to direct searches for sub-GeV mass dark matter.


19-01-2018 : Chris Backhouse (UCL)

New results from NOvA

The phenomenon of neutrino oscillations, which implies that neutrinos are not massless as we had previously believed, raises a wealth of new and intriguing questions. What is the ordering of the neutrino mass states? Might neutrino oscillations violate matter/antimatter symmetry? What structure, if any, does the neutrino mixing matrix have? The NOvA experiment directly addresses these questions by measuring the changes undergone by a powerful neutrino beam over an 810 km baseline, from its source at Fermilab, Illinois to a huge 14 kton detector in Ash River, Minnesota. I will give a brief overview of neutrino oscillations, then present updated NOvA measurements of the disappearance of muon neutrinos and their transformation into electron neutrinos, the implications of these results, and prospects for the future.