UCL HEP Seminars 2017
15/12/2017 : Silvia Pascoli (Durham)
Going beyond the standard 3-neutrino mixing scenario
Although the standard 3 neutrino mixing scenario fits very well most existing data, the possibility that new effects, e.g. sterile neutrinos, NSI…, exist is still open. In this talk I will focus mainly on sterile neutrinos. They are neutral fermions which do not have Standard Model interactions but mix with light neutrinos. They constitute a minimal extension of the standard model. They have interesting signatures in cosmology and in laboratory searches. I will review the current situation, discussing the hints for their existence and their tests in neutrino oscillation, beam dump, SBN, DUNE and other experiments. I will conclude presenting a possible explanation of the MiniBooNE excess which is compatible with current data.
08/12/2017 : NOTE UNUSUAL TIME & PLACE: 3pm Massey: Mauricio Bustamante (Niels Bohr Institute)
Heaven-sent neutrino interactions from TeV to PeV
Neutrino interactions are vital to particle physics and astrophysics. Yet, so far, they had remained unprobed beyond neutrino energies of 350 GeV. Now, thanks to the discovery of high-energy astrophysical neutrinos by IceCube, we have measured neutrino-nucleon cross sections from a few TeV up to a few PeV. We did this by using the Earth itself as a target: neutrino interactions with matter inside the Earth imprint themselves on the distribution of neutrino arrival directions at the detector. When measuring high-energy particle interactions, the sky is the limit.
01/12/2017 : Anthony Hartin (UCL)
Strong field QED effects in the quantum vacuum generated by laser-electron interactions
When considered in a non-perturbative QFT, the interactions of intense lasers and relativistic charged particles lead to novel strong field QED effects amenable to experimental tests with available technology. I review the theory and simulation strategy necessary in order to design discovery experiments for these effects. The intense laser field is taken into account exactly in the bound Dirac equation whose solutions are required for different field configurations. The simulation strategy requires a PIC code combined with a monte-carlo of the quantum interactions. The workhorse process for such experiments is the trident process which I will also review.
24/11/2017 : Mitesh Patel (Imperial)
Anomalous measurements at the LHCb experiment
A number of measurements of B-meson decays made at the LHCb experiment give anomalies with respect to the predictions of the Standard Model. The status of the relevant measurements, the connections between them and their theoretical interpretation will be discussed, along with the prospects for the future.
17/11/2017 : Pontus Stenetorp (UCL)
DIS CDT seminar: Artificial Intelligence for Reading the Scientific Literature
We are currently experiencing an unprecedented increase of interest in applying Artificial Intelligence methods for various tasks. Spurred on advances using modern reincarnations of neural networks – Deep Learning – machine learning-based approaches have seen recent successes in complex games like Go, autonomous vehicles, and language-based question answering. In this talk I will present the current state of the art in Natural Language Processing (NLP) and its limitations. I will then relate this to previous and ongoing efforts in applying NLP-methods to the scientific literature – allowing scientists to cope with an ever increasing number of publications. Primarily I will cover ongoing work from the UCL Machine Reading group on text-based multi-step inference applied to the biomedical literature and a collaboration with the UCL Space & Climate Physics to track astronomical measurements in the astrophysics literature.
10/11/2017 : John LoSecco (Notre Dame)
The History of the Atmospheric Neutrino Anomaly
This talk covers the early days of particle astrophysics when it was slowly realized that the major background to proton decay, atmospheric neutrino interactions, were an important discovery in their own right.
03/11/2017 : Moritz Backes
Recent results from Supersymmetry Searches at ATLAS
This talk discusses a selection of the latest ATLAS results for searches for supersymmetric (SUSY) particles performed with pp collisions at a centre-of-mass energy of 13 TeV, using the full 2015 and 2016 dataset. Weak and strong production of SUSY particles in both R-Parity conserving and violating scenarios are considered assuming either prompt decays or longer-lived states.
27/10/2017 : Jens Dopke (RAL)
Reading charcoal: Using HEP detectors to decipher papirii
I will introduce the problem of reading ancient documents, in this particular project working on reconstruction of text from scrolls found in Herculanuem near Mt. Vesuvis. These are made from papyrus and have been written on using organic inks. After the eruption of Mt. Vesuvius in 79 AD, these been slow-cooked under exclusion of oxygen, and hence turned into lumps of charcoal. All attempts of unrolling these subjects have been destructive. First indications show that dark-field x-ray imaging allows to make the ink of these documents visible and there is good hope that this assumption holds for multi-layered documents that cannot be unrolled. I will introduce dark-field x-ray imaging, report on where we are with the project, what’s lacking at the moment and where we plan to get to within the next year(s).
20/10/2017 : Valerio Dao: NOTE: unusual time and location: 3pm Harrie Massey
Physics with Hbb at ATLAS
Since its discovery in 2012 the Higgs boson particle has opened new possibilities to further improve our understanding of the Standard Model physics landscape. Precise characterisation of its production and its properties could be used to indirectly probe for new physics effects and, at the same time, the decay of new particles could directly lead to signatures with a SM-like Higgs boson in the final state. The decay of the Higgs boson into a b-quark pair has, in this respect, a key role; while experimentally very challenging, the large branching ratio makes it the largest contributor to the total width of the Higgs boson and, thanks to the large rate, provides the best chance to see evidence for new phenomena that lead to deviations at high pT. Recently the ATLAS collaboration achieved an important milestone by obtaining the evidence for the H->bb decay in the associated production of the Higgs boson and a vector boson using Run2 data at 13 TeV. This seminar will mainly focus on this recent result discussing the experimental challenges that have been faced to extract the signal from a very large background. In addition, key examples of how H->bb signature could be used for directly searching for new physics effects will be given.
01/09/2017 : Evan Niner (Fermilab)
Deep Learning Applications of the NOvA Experiment
The NOvA experiment is a long-baseline neutrino oscillation experiment that uses two detectors separated by 809 kilometers to measure muon neutrino disappearance and electron neutrino appearance in the beam produced at Fermilab. These oscillation channels are sensitive to unknown parameters in neutrino oscillations including the mass hierarchy, θ23, and CP violation. In this talk I will focus on the development and application of deep learning algorithms to the task of event reconstruction and classification in NOvA. These algorithms, adapted from computer vision applications, resulted in a performance gain equivalent to a 30% increase in exposure in the 2016 analysis. I will also look at future deep learning applications.
12/07/2017 : Steven Prohira (Kansas University)
Radio interactions with particle-shower plasmas, with implications for high-energy astro-particle physics
The collision of a high-energy particle with stationary matter, such as ice, results in a shower of secondary particles. As these secondary particles traverse the interaction medium, cold ionization electrons are produced. For high enough primary particle energies, this cloud of ionization electrons is dense enough to form a tenuous plasma which may reflect radio-frequency (RF) energy. As such, RF scatter techniques have been proposed as a robust technology to remotely detect such high-energy particle interactions by illuminating a detection volume with RF energy and remotely monitoring the same volume for a reflected RF signal from a particle-shower plasma. Though the Telescope Array RADAR (TARA) experiment, the first dedicated attempt at the radio-scatter method, yielded no results, the intriguing lack of signal has caused renewed interest in the technique. Surprisingly, a dedicated laboratory measurement of RF scatter from particle-showers has never been performed at high (GeV) energies. This talk will discuss experimental results from TARA and will detail a laboratory measurement to take place at the End-Station facilities at SLAC to quantify the parameters of the particle-shower plasma. A high-energy electron beam will be fired into a large target to initiate a shower from which RF will be reflected. The observables from this measurement will be discussed, along with outlook.
23/06/2017 Prof. Tsutomu Yanagida (IPMU, U. of Tokyo)
The Origin of Matter in the Universe
Paul Dirac proposed the baryon symmetric universe in 1933. This proposal has become very attractive now since it seems that all pre -existing asymmetry would have been diluted if we had an inflationary stage in the early universe. However, if our universe began baryon symmetric, the tiny imbalance in numbers of baryons and anti-baryons which leads to our existence, must have been generated by some physical processes in the early universe. In my talk I will show why the small neutrino mass is a key for solving this long standing problem in understanding the universe we observe today.
16/06/2017 Sarah Bridle (Manchester)
Gastrophysics: Food security for astro/physicists
In this seminar I will describe my motivations for being interested in food research, and my belief that STFC researchers bring a lot of relevant skills to the challenges of providing food that consumers want. The STFC Food Network+ aims to bring STFC researchers and facilities together with food researchers and industry, through network meetings and funding for new projects. Some background about food: There is an impending perfect storm of pressure on our food production system, with increasing population and changing consumer tastes, in the face of rising temperatures and extreme weather events. Tim Gore, head of food policy and climate change for Oxfam, said “The main way that most people will experience climate change is through the impact on food: the food they eat, the price they pay for it, and the availability and choice that they have.”. Yet, at the same time, food production is a bigger contributor to climate change than transport. A 2014 Chatham House report states “Dietary change is essential if global warming is not to exceed 2C.”.
02/06/2017 : Edward Daw (Sheffield)
Axions and Axion-Like Particles
In recent years, searches for new physics beyond the standard model have focussed on the electroweak scale, using channels that are reachable in high energy accelerators and through induced interactions of hypothesised electroweak-scale relic particles (WIMPs) in tonne-scale direct search experiments. A second possibility which is scientifically just as well-motivated is that the dark matter consists of much lighter pseudoscalars, called axions, whose origin is in low energy quantum chromodynamics, whose coupling to ordinary matter is feeble because their low mass, and consequently their feeble couplings to other particles, renders them 'invisible' to ordinary accelerator searches. The same feeble couplings mean that axions have very long decay times, so that relic axions generated in the very early Universe may be the dark matter evidenced through its gravitational effects today. I shall survey the field of axion-sector experimental searches. Experiments that look directly for the axion itself attempt to induce dark matter axions to convert into microwave photons in closed electromagnetic resonators. Other experiments identify other by-products of the symmetry breaking mechanism that may have yielded axions; these other by-products are sometimes called ALPs (axion-like particles), and experiments to search for ALPs typically use a 'light shining through a wall' technique. Overall this is an exciting and growing field. I will also discuss some of my own work on axion searches with the ADMX experiment, aimed towards improvements in the sensitivity and search rate of such experiments by means of novel modifications to the resonant detector design.
26/05/2017 : Leigh Whitehead (CERN)
Sterile Neutrino searches with MINOS and MINOS+
Three-flavour neutrino oscillations have proved very successful in describing the observed neutrino oscillation data. However, there are also some anomalies, including the excesses of appeared electron neutrino interactions in LSND and MiniBooNE, and a sterile neutrino state at a larger mass-splitting scale can provide an explanation for these results. The MINOS/MINOS+ experiment was a long-baseline neutrino experiment in the US, collecting beam and atmospheric neutrino interactions from 2003 until 2016. MINOS was optimised for the study of muon neutrino disappearance in the NuMI beam at Fermilab. The continuation of the experiment with a medium energy beam configuration is called MINOS+. A sterile neutrino in MINOS/MINOS+ would appear as a modulation on the three-flavour oscillations. A search for sterile neutrinos has been performed using charged-current and neutral-current interactions in two detectors separated by a distance of 734km. The inclusion of two years of MINOS+ data and an improved fit method provides a much increased sensitivity over the previous MINOS result that was combined with Daya Bay.
19/05/2017 : Gabriel Facini (UCL)
Searches for new phenomena with the ATLAS detector
Many theories beyond the Standard Model (BSM) predict new phenomena accessible by the LHC which prevent the need of fine-tuning of the Higgs Boson mass or expand the gauge sectors of the SM or the nature of Dark Matter for example. Searches for new physics models are performed using the ATLAS experiment at the LHC focusing on exotic signatures that can be realized in serval BSM theories. The results reported use the pp collision data sample collected in 2015 and 2016 by the ATLAS detector at the LHC with a centre-of-mass energy of 13 TeV.
05/05/2017 : Christopher McCabe (GRAPPA)
Low energy signals in xenon detectors: from supernova neutrinos to light dark matter
One of the major achievements of the LUX collaboration was to accurately calibrate xenon dark matter direct detection experiments to sub-keV energies. This means that reliable predictions of low-energy signals can now be performed. In this talk, I’ll explore new low-energy signals from neutrinos and low-mass dark matter that could be measured with the forthcoming generation of multi-tonne xenon detectors. Based primarily on arXiv:1606.09243 and arXiv:1702.04730.
28/04/2017 : Tommi Tenkanen (QMUL)
Observational properties of feebly interacting dark matter
Can dark matter properties be constrained if dark matter particles interact only feebly with the Standard Model fields? The answer is yes. By studying both cosmological and astrophysical constraints, we show that stringent constraints on dark matter properties can be derived even in case the dark matter sector is practically uncoupled from the Standard Model sector. By taking the Higgs portal model as a representative example, we study in detail scenarios where the hidden sector does not thermalize with the Standard Model sector and, among other things, derive a lower bound on dark matter self-interaction strength.
21/04/2017 : Jonas Lindert (IPPP Durham)
High-precision predictions for V+jet production
In LHC searches for Dark Matter one of the dominant systematic uncertainties arises from the determination of the irreducible Z(->vv)+jet background. The modelling of this background relies on accurate measurements of V+jet production processes with visible final states and their extrapolation to the signal region via a global fit based on high-precision Standard Model predictions for pp->W+jets, pp->Z+jets and pp->gamma+jets including higher-order QCD and EW corrections. I will present such predictions with a focus on the mandatory determination of robust estimates of remaining theoretical uncertanties at the percent level and their correlation amongst processes.
07/04/2017 Luise Skinnari(Cornell)
Track-triggering at CMS for the High-Luminosity LHC
The high luminosity upgrade of the LHC, scheduled for 2024-2025, will increase the luminosity by a factor of 10 beyond the original LHC design. The resulting large datasets will allow precise measurements of Higgs properties, searches for rare processes, and much more. To cope with the challenging environment from the high luminosity, significant upgrades will be required for the LHC experiments. A key upgrade of the CMS detector is to incorporate tracking information in the hardware-based trigger. We are exploring different strategies for performing the hardware-based track finding, including a fully FPGA-based approach. I will give an overview of the CMS track trigger upgrade, describe its expected performance, and show results from developments of a hardware demonstrator system.
31/03/2017 Andreas Warburton (McGill/[UCL])
Searches for New Physics on the Intensity Frontier: The Belle II Experiment
The Belle II collaboration comprises over 600 physicists from 23 countries building a detector on the high-luminosity SuperKEKB electron-positron collider in Japan. The detector, a successor to the successful BaBar and Belle experiments, has capabilities complementary to efforts with similar goals at the LHC and is the latest experimental tool in the now three-decade-long B-factory era. I will outline the prospects for discoveries of new physics at Belle II and discuss the latest status and schedule of the accelerator and detector upgrades, currently in progress.
24/03/2017 : Jose No (KCL)
Beyond simplified models for dark matter searches @LHC: Making a case for the pseudoscalar portal
The Higgs sector is a well-motivated portal to dark matter (DM). I discuss scalar/pseudoscalar portal models for DM, as a powerful tool to exploit the complementarity between LHC searches and direct/indirect DM detection experiments, and their connection to Higgs physics. I then analyze the shortcomings of so-called "simplified DM models" in this context, highlighting the key physics these models fail to capture and its impact on LHC searches.
10/03/2017 Mark Lancaster (UCL)
The Fermilab Mu2e Experiment
In the SM the only mechanism to violate charged lepton flavour conservation is via neutrino oscillations which results in a branching rate for neutrinoless muon interactions of order 10^-50. As such any observation of a neutrinoless muon interaction would be evidence of new physics. In this talk I will describe the Fermilab Mu2e experiment that is seeking to detect the neutrinoless conversion of a muon to an electron in the field of a nucleus using 10^20 muons with a branching ratio sensitivity down to 6x10^-17 : a factor of 10^4 better than the previous limit which allows the experiment to probe new physics mass scales up to 8000 TeV, well beyond that probed by direct searches at the LHC.
03/03/2017 Fady Bishara (Oxford)
The next frontier for Higgs couplings
The LHC experiments have, so far, measured many of the Higgs couplings and found excellent agreement with the minimally-realized electroweak symmetry breaking (EWSB) mechanism in the Standard Model. Nevertheless, there are important couplings that are currently out of reach which test the nature of EWSB and fermion mass generation. This talk will focus on two of them: the charm Yukawa and the hhVV couplings. A measurement of the first would confirm that the 125 GeV Higgs which gives mass to third generation fermions also gives mass the second generation. To this end, I will describe recent ideas to probe the charm Yukawa coupling in particular by using Higgs differential distributions. In the second case, deviations of the hhVV coupling from the SM would signal non-linearity and herald new physics at higher energies. As I will show, double Higgs production in VBF at the LHC can provide such a test at the 20% level by the end of the high luminosity run while a percent level constraint can be obtained at a future circular collider.
10/02/2017 Mercedes Paniccia (Geneva)
The Alpha Magnetic Spectrometer on the International Space Station: the era of precision cosmic-ray physics
The Alpha Magnetic Spectrometer (AMS) is the most powerful and sensitive cosmic-ray detector ever deployed in space to produce a complete inventory of charged particles and nuclei in cosmic rays near Earth in the energy range from GeV to few TeVs. Its physics goals are the study of cosmic-ray properties, indirect search for Dark Matter and direct search for primordial antimatter. The improvement in accuracy over previous measurements is made possible through its long duration time in space, large acceptance, built in redundant systems and its thorough pre-flight calibration in the CERN test beam. These features enable AMS to analyse the data to an accuracy of ~1%. Since its installation on the International Space Station in May 2011, AMS has collected more than 90 billion cosmic-ray events and has produced precision measurements of electron, positron, proton, antiproton, He and light nuclei fluxes and of their ratios in cosmic rays of energy ranging from GeV to few TeVs. The percent precision of the AMS results challenges the current understanding of the origin and of the acceleration and propagation mechanisms of cosmic rays in the galaxy and thereby requires new theories to be developed by the physics and astrophysics community. In this talk, after a brief introduction to cosmic-ray physics, I will present the latest AMS results based on its first five years of data taking, pointing out their implication for cosmic-ray modelling and for Dark Matter searches.
27/01/2017 : Jan Kretzschmar (Liverpool)
Precision W and Z cross-sections and the first measurement of the W boson mass at ATLAS
The Large Hadron Collider has produced more W and Z bosons than any other collider before. The large samples of leptonic bosons decays provide a unique opportunity for precision studies of the strong interaction and the electroweak interaction. These studies are facilitated by the high experimental precision achieved in these measurements after a careful detector calibration. New cross-section measurements allow novel insights into the proton structure. Specifically, strong constraints of the poorly known strange-quark distribution are demonstrated in a NNLO QCD analysis. The mass of the W boson is a key parameter in the global electroweak fit to test the overall consistency of the Standard Model. The first complete W-boson mass measurement at the LHC is presented, which requires an extraordinary control over both experimental and theoretical effects.
20/01/2017 Jon Butterworth (UCL)
Making measurements and constraining new physics at the LHC
Particle-level differential measurements made in fiducial regions of phase-space at colliders have a high degree of model-independence. These measurements can therefore be compared to BSM physics implemented in Monte Carlo generators in a very generic way, allowing a wider array of final states to be considered than is typically the case. A new method providing general consistency constraints for Beyond-the-Standard-Model (BSM) theories, using measurements at particle colliders, is presented.
09/01/2017 Jordan Myslik (LBNL) NOTE: UNUSUAL DATE/PLACE!!! Physics E7
The MAJORANA DEMONSTRATOR
Abstract: The MAJORANA DEMONSTRATOR is an experiment searching for neutrinoless double-beta decays of germanium-76. This lepton-number-violating process is connected to the nature, absolute scale, and hierarchy of the neutrino masses. The MAJORANA DEMONSTRATOR consists of two modular arrays of natural and 76Ge-enriched germanium detectors totalling 44.1 kg, located on the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota. While seeking to demonstrate backgrounds low enough to justify a tonne-scale experiment and the feasibility of its construction, the MAJORANA DEMONSTRATOR's ultra-low backgrounds and excellent energy resolution also allow it to probe additional physics beyond the Standard Model. This talk will discuss the physics and the design elements of the MAJORANA DEMONSTRATOR, its results to date, and its future prospects, along with the plans for a future 1 tonne germanium-76 neutrinoless double-beta decay experiment.