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HEP Seminars

09 Apr 2020

UCL HEP Seminars 2015

11/12/2015 Dr. Juan Rojo (Oxford)

Reduction strategies for the combination of PDF sets and the PDF4LHC15 recommendations

We discuss recently developed strategies for the statistical combination of PDF sets. These methods allow to combine the predictions of many different PDF sets into a single combined set, in terms of optimized sets of Hessian eigenvectors or Monte Carlo replicas. These combination strategies have been used for the implementation of the 2015 PDF4LHC recommendations, required for the estimation of the total PDF+alphas uncertainties for LHC cross-sections at Run II. We discuss the improvements as compared to the 2011 PDF4LHC prescription, and the impact of the new prescription on precision measurements at Run II.

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04/12/2015 Dr. Sofiane Boucenna (Frascati)

Common Frameworks for DM and Baryogenesis

The nature of dark matter (DM) and the origin of the baryon asymmetry of the Universe (BAU) are two enduring mysteries in particle physics and cosmology. Many approaches have been developed to tackle them simultaneously leading to diverse models and paradigms, such as Asymmetric dark matter (ADM). In the first part of the talk I will give a (brief) overview of what has been done so far, highlighting the important concepts of these constructions. Then, in the second part, I will present a new framework relating the weakly interacting massive particles paradigm to ADM in a minimal and model-independent way.

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27/11/2015 Frank Tackmann (DESY)

XCone: N-jettiness as an Exclusive Cone Jet Algorithm

I will discuss a new jet algorithm XCone, which is based on minimizing the event shape N-jettiness and has several attractive features. It is exclusive and always returns a given fixed number of jets. Well-separated jets are conical and practically identical to anti-kT jets of the same size. Overlapping jets are automatically partitioned by nearest-neighbor. In this way, XCone allows to smoothly transition between the resolved regime where all jets are well separated and the boosted regime where they overlap. It also inherits the theoretical factorization properties of the underlying N- jettiness variable. I will show examples of its application for dijet resonances, Higgs decays to bottom quarks, and all-hadronic top pairs.

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20/11/2015 Katharine Leney (UCL)

Searching for Di-Higgs→bbττ at ATLAS

Several models for new physics predict TeV scale resonances that decay to pairs of Higgs bosons. This talk will review the ATLAS search for pair-produced Higgs bosons decaying to bbττ final states using 20 fb-1 proton-proton collision data with √s = 8 TeV and present the combination of all Run 1 ATLAS di-Higgs searches. I will also review the prospects for di-Higgs searches in the bbττ channel for Run 2 and beyond.

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13/11/2015 Geoff Hall (Imperial)

Tracking and trigger upgrades of CMS

CMS will upgrade its trigger during the forthcoming 13 TeV run to maintain performance under increasingly challenging pileup conditions due to the success of the LHC machine in delivering high luminosity collisions. In the longer term, a new tracker is proposed for installation around 2023, which will for the first time provide data to be used in the L1 trigger. LHC data taking is expected to continue until well into the 2030 decade. The motives for these developments and progress towards them will be explained.

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06/11/2015 Sarah Malik (Imperial)

Review of the status and future prospects of dark matter searches at colliders

Understanding the nature of dark matter is one of the most compelling, long standing questions in physics. Reports of possible dark matter signals from several direct detection experiments have further highlighted the need for independent verification from non-astrophysical experiments, such as colliders. I will review the results of searches for dark matter at CMS in Run 1 of the LHC, what we can expect in Run 2 and beyond, as well as recent developments in dark matter phenomenology.

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30/10/2015 Doug Cowen (Penn State)

High Energy Atmospheric Neutrino Appearance and Disappearance with IceCube

The IceCube neutrino observatory, buried deep in the ice at the South Pole, has detected neutrinos that span over five orders of magnitude in energy. Fulfilling one of its original stated goals of discovering cosmological ultrahigh energy neutrinos, its large instrumented volume also provides us with a surprisingly powerful instrument for studying neutrino oscillations with an unprecedented statistical sample of energetic atmospheric neutrinos. In this presentation we will describe the IceCube detector and focus on its current and future atmospheric neutrino oscillation measurements with DeepCore, IceCube's low-energy in-fill array. We will also describe a new proposed low-energy extension, the Precision IceCube Next Generation Upgrade (PINGU), highlighting its ability to measure one of the remaining fundamental unknowns in particle physics, the neutrino mass hierarchy.

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23/10/2015 Gavin Hesketh (UCL) UNUSUAL PLACE/TIME
16.15 Auditorium XLG2 | Christopher Ingold Building

Life after the Higgs: Where next for particle physics?

The Large Hadron Collider, the world's largest particle accelerator, recently restarted after a 2 year break. Smashing protons together at almost twice the energies previously achieved, the data taken next few years may reveal more about the fundamental building blocks of the universe. But, with the discovery of the Higgs Boson in 2012, the theory of these building blocks, the Standard Model, was "completed". So what could we hope to learn next, either at the LHC or elsewhere? http://events.ucl.ac.uk/event/event:hbc-icokdek5-siapwd/life-after-the-higgs-where-next-for-particle-physics

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16/10/2015 Louis Lyons (Oxford/Imperial)

“Statistical Issues in Searches for New Physics

Given the cost, both financial and even more importantly in terms of human effort, in building High Energy Physics accelerators and detectors and running them, it is important to use good statistical techniques in analysing data. This talk covers some of the statistical issues that arise in searches for New Physics. They include topics such as:

  • Blind analyses
  • Significance
  • Should we insist on the 5 sigma criterion for discovery claims?
  • $P(A|B)$ is not the same as $P(B|A)$.
  • The meaning of $p$-values.
  • Example of a problematic likelihood.
  • What is Wilks' Theorem and when does it not apply?
  • How should we deal with the `Look Elsewhere Effect'?
  • Dealing with systematics such as background parametrisation.
  • Coverage: What is it and does my method have the correct coverage?
  • Combining results, and combining $p$-values
  • The use of $p_0$ v $p_1$ plots.
This is an extended version of a talk given at the LHCP2014 Conference in New York in June 2014.

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09/10/2015 Linda Cremonesi (UCL)

Neutrino interactions at the T2K near detector complex

The T2K long-baseline neutrino oscillation experiment observed electron neutrino appearance in 2011 and reported the first results of a search for electron anti-neutrino appearance in 2015. Systematic uncertainties relating to the models of neutrino interactions on atomic nuclei are increasingly problematic as the precision of oscillation measurements improves. Interaction cross-section measurements are therefore vital for the correct interpretation of neutrino data, and consequently reducing the uncertainties on the oscillation measurements. The near detector complex of T2K, with scintillating tracking detectors on-axis (INGRID) and a magnetised fine-grained tracking system off-axis (ND280), offers a unique opportunity to study neutrino interactions in the region of 0.6~1GeV. In this seminar I will report the latest cross-section measurements performed at ND280 and INGRID, which include muon neutrino charged current interactions on different targets (scintillator or water) and with various final states (inclusive, zero pion, one pion and coherent pion production). I will illustrate the value of this data and the difficulties that still remain.

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27/08/2015 Foteini Oikonomou (Penn State)

Note: Unsual time/date 2pm:
A multi-messenger quest for the sources of the highest energy cosmic rays

The sources of cosmic rays with energy exceeding 10^18 electron volts remain unknown, despite decades of observations. The discovery of the sources of these fascinating cosmic messengers, termed ultra-high energy cosmic rays (UHECRs), will unravel the workings of the Universe's most violent accelerators. I will discuss the constraints imposed by UHECR observations on their sources, focusing on the arrival direction distribution of the UHECRs detected at the Pierre Auger observatory. Constraints on the sources of UHECRs are also imposed by observations of the secondary particles (gamma-rays and neutrinos) that UHECRs produce during their propagation in the intergalactic medium. By way of illustration, I will present models of UHECR emission in blazars, and discuss the detectability of the signatures of such (hadronic) processes in blazar gamma-ray spectra. Finally, I will present the current status of experimental efforts to pin down the origin of UHECRs, by detecting UHECR, neutrino, and electromagnetic transient emission, through real-time coincidence searches, within a global, multi-messenger, alert network.

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19/06/2015 : Diego Aristizabal (Université de Liège)

Neutrino masses beyond the tree level

The standard approach to Majorana neutrino masses relies on the type-I seesaw, where neutrino masses are induced through tree level exchange of heavy right-handed neutrinos. Other scenarios, however, are possible and they typically offer testable predictions and in some cases even connections with dark matter. In this talk, after reviewing some well-known loop-induced neutrino mass models, I will discuss a generic approach for two-loop-induced neutrino masses. Finally, I will comment on some possible "generic" accelerator tests of these scenarios.

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12/06/2015 : Alex Martyniuk (UCL)

Search for diboson resonances at ATLAS using boson-tagged jets

With the advent of 13TeV proton-proton collisions at the LHC it is natural to trawl through this data searching for new resonances with the highest possible masses. Do we have any clues of what we might expect in this new energy regime? An ATLAS paper released in the dying moments of LHC Run-1* offers us a possible direction. This paper describes a search for a heavy resonance (either a W’ or Kaluza-Klein Graviton) decaying into a diboson pair, leading to highly boosted hadronic jets. By exploiting jet substructure techniques to pick the signal out of the dominant QCD backgrounds the analysis can take advantage of the high branching fraction enjoyed by the fully hadronic decay channel. In this seminar I will describe the jet-substructure techniques explored by the analysis, present the results of the analysis of the 20fb^-1 of 8TeV ATLAS data and finally look to the prospects with the new collision data.

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05/06/2015 : Yue-Lin Sming Tsai (IPMU)

Singlet Majorana fermion dark matter: LHC14 and ILC

Exploring a dark matter (DM) candidate using an effective field theory (EFT) framework is a popular approach. However, since the central energy of LHC is going to be 14 TeV and future ILC experiment could also reach 1 TeV, the EFT is not valid any more. In this talk, I will first review our previous work, 1407.1859, then show how we conservatively estimate the power LHC&ILC on EFT by comparing with the UV completed model.

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29/05/2015 Ben Cooper/David Wardrope (UCL)

Searching for new physics with di-Higgs to 4b final states at ATLAS.

It is not often these days that a completely new channel is developed to search for evidence of new physics at the LHC. When Run-1 of the LHC began, the general consensus was that, compared to final states containing leptons, fully hadronic final states would not be competitive in the search for new physics, because the enormous QCD backgrounds would be overwhelming. In this seminar we will tell the story of how this notion was reversed for Higgs pair production, present the latest Run-1 results of the di-Higgs to 4b searches by ATLAS and CMS, and give the prospects for exploiting this channel in the future, including the potential for dramatically extending the physics reach of the HL-LHC.

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22/05/2015, Leigh Whitehead (UCL) NOTE UNUSUAL TIME: 12.30 !!!

The CHIPS Experiment

CHIPS (Cherenkov Detectors In mine PitS) is an R&D project aiming to blaze the trail towards affordable megaton scale neutrino detectors whilst contributing to the world knowledge on the neutrino mass hierarchy and delta_cp. The first step on the way to this goal was the deployment of CHIPS-M, a small prototype in an open mine pit in northern Minnesota, exposed by the NuMI beam from Fermilab. The second 10 kton prototype, CHIPS-10, is in the design process and is due for deployment in the summer of 2016. CHIPS-10 combined with NOvA and T2K will give over three sigma sensitivity to the mass hierarchy and delta_cp. I will give an overview of the experiment, show the first data from CHIPS-M, and discuss the design of CHIPS-10 and our plans for the future.

15/05/2015, Josef Pradler (HEPHY Vienna)

Dark Vectors in Cosmology and Experiment

More often than not, astrophysical probes are superior to direct laboratory tests when it comes to light, very weekly interacting particles, and it takes clever strategies and/or ultra-pure experimental setups for direct tests to be competitive. In this talk, I will highlight this competition on the example of dark photons. When they are dark matter, direct detection probes can be superior to stellar constraints. When they decay, cosmology offers unique sensitivity through BBN and CMB.

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30/04/2015 note: unusual DATE: Alain Blondel (Geneva)

CERN: the next 60 years and 100 kilometers

CERN is hosting the design study of Future Circular Colliders fitting in a new tunnel of 100km circumference around Geneva. A possible first step is the "Electroweak Factory", a high luminosity electron-positron (lepton) collider covering the energy range from the Z pole to above the top threshold, for the study of several TeraZ, okuW, MegaHiggs and Megatops. The tunnel would fit, as ultimate goal, a 100 TeV pp collider. The project will be described with special attention to the electron machine. The combination of the two machines offers a remarkable potential for discoveries, from a blend of precision measurements, high statistics, high energies and sensitivity to very small couplings. In particular the search for sterile right-handed neutrinos (aka neutral heavy leptons), with mass up to the Z mass, will be shown to reach couplings as small as predicted by the see-saw limit.

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17/04/2015 Deepak Kar (Glasgow/TBC)

All about showering at the LHSea!

Improving the parton shower model in Monte Carlo generators is important for precision measurements as well as for searches at the LHC. ATLAS and CMS performed many interesting measurements sensitive to to non-perturbative QCD effects and compared the results with existing MC models and tunes, and clear discrepancies and new features have been observed in many cases. All these data are being used in improving the modelling. Also, many jet substructure techniques depend on modelling the shower accurately, and I will briefly discuss one such technique, called shower deconstruction, and the promising results it yields.

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10/04/2015 Cheryl Patrick (NorthWestern)

Neutrino-nucleus interactions at MINERvA

Fermilab's MINERvA experiment is designed to make precision measurements of neutrino scattering cross sections on a variety of materials. After introducing the MINERvA detector, I will explain why these measurements are so important to the current neutrino program. I will then describe several recently published results that are already being used by the neutrino community to improve their modelling of neutrino interactions, focusing particularly on the quasi-elastic analysis. There will also be a chance to look at interesting analyses that will be published in the coming months, and at the plans for MINERvA's longer-term future.

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27/03/2015 UCL HEP Students

IOP practise talks

Note unusual start time: 2pm

20/03/2015 Phillip Litchfield (UCL)

The AlCap experiment // A tour of muon physics from NuFact

The AlCap experiment is a joint project between the COMET and Mu2e collaborations. Both experiments intend to look for the lepton-flavour violating conversion μ+A→e+A, using tertiary muons from high-power pulsed proton beams. In these experiments the products of ordinary muon capture in the muon stopping target are an important concern, both in terms of hit rates in tracking detectors and radiation damage to equipment. The goal of the AlCap experiment is to provide precision measurements of the products of nuclear capture on Aluminium, which is the favoured target material for both COMET and Mu2e. The results will be used for optimising the design of both conversion experiments, and as input to their simulations. Time allowing, I will also present a (necessarily brief) tour of active and planned muon experiments, as presented at NuFact. The muon is something of a special case. Although we know there are three generations of Standard Model particles, the world around us is essentially built up from the first generation. The low mass and correspondingly long lifetime of the muon means that is one of very few higher-generation particles that can be manipulated for study, and as such provides a complimentary window to the standard 'brute force' approach of bringing first-generation particles together at ever higher energies and intensities. I will give a very brief summary of the muon projects discussed at NuFact 2014.

13/03/2015 Jennifer Jentzsch (Dortmund)

Quality assurance measurements during the ATLAS Insertable B-Layer production and integration

The ATLAS Detector is one of the four big particle physics experiments at CERN's LHC. Its inner tracking system consisted of a 3-Layer silicon Pixel Detector (~ 80M readout channels) in the first run (2010-2012) and has been upgraded by an additional layer over the last two years. The Insertable B-Layer (IBL) adds ~12M readout channels for improved vertexing, tracking robustness and b-tagging performance for the upcoming runs before the high luminosity of the LHC will take place. The active part of the detector is roughly 66cm long and consists of 14 parylene coated carbon foam support structures, so-called staves, at an average distance of 33.25mm away from the beam. The IBL includes new sensor and readout chip designs finding their first application in high energy physics experiments. Production accompanying measurements as well as preliminary results after integration into the ATLAS Detector, right before the start of the second LHC run, will be presented and discussed.

11/03/2015 : Jenny Thomas : 4pm Harrie Massey LT

XXV Spreadbury Lecture : Neutrino Oscillations At Work

The observation that the three types of neutrino flavour oscillate among themselves led to the realisation that neutrinos have a very small but non-zero mass. This is extremely important because the supremely successful Standard Model of particle physics had expected, and indeed needed, the neutrinos to have exactly zero mass. Since the discovery of neutrino oscillations over the last 15 years, the parameters of the oscillations have been sufficiently well measured to turn neutrino oscillations into a tool for learning more about the elusive neutrino. I will explain the concept of neutrino oscillations, and report on the recent results from around the world and the new challenges now facing researchers trying to infer the remaining unknown neutrino properties. I will talk briefly about an exciting new project on the horizon for the very near future.

06/03/2015 Freya Blekman (Brussels)

Exploring new physics in the Top quark sector using Beyond-Two-Generations Quarks with the Compact Muon Solenoid

In many models of physics beyond the Standard model the coupling of new physics to third generation quarks is enhanced or signatures are expected that mimic top production. I will present a review of mostly non-MSSM-inspired searches for new physics beyond the standard model in final states containing top quarks or bottom quarks performed by the CMS experiment. Many of these techniques used have solid roots in precision measurements of the standard model, and applying these techniques from measurements to searches has opened a rich and varied searches program in the CMS experiment. Examples include searches for heavy gauge bosons, excited quarks, sequential and vector-like top quark partners. The analyses span a range of final states, from multi-leptonic to entirely hadronic, and many use convoluted analysis techniques to reconstruct the highly boosted final states that are created in these topologies. I will focus on the recent results, using data collected with the CMS experiment in proton-proton collisions at the LHC at a centre-of-mass energy of 8 TeV.

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27/02/2015 Anastasia Basharina-Freshville (UCL)

Calorimetry for Cancer Proton Therapy - Can We Help?

Proton therapy is an advanced form of radiotherapy that provides significantly improved cancer treatment to patients. In Summer 2015 UCLH will commence the building of a 250 MeV proton beam treatment centre. Challenges currently exist in the field of proton therapy, such as the requirements of precise measurements of the beam energy and spread. We address some of these challenges using a calorimeter module designed for the SuperNEMO experiment, which we have tested at the only currently running proton treatment beam in the UK at the Clatterbridge Centre for Oncology.

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20/02/2015 Andrea Banfi (Sussex)

A general method for final-state resummations in QCD

We present a novel method that makes it possible to resum event-shape distributions and jet rates at NNLL accuracy. We present results for suitable observables in e+e- annihilation and discuss the generalisation of the method to hadron-hadron collisions and higher logarithmic accuracy.

13/02/2015 : Adam Gibson (UCL)

Tracking emissions during proton therapy

Proton radiotherapy uses a beam of protons at up to 250 MeV to deliver a dose of ionising radiation to the body, usually with the intention to cure cancer. The physics of proton interactions with tissue provides a particular advantage: most of the energy is deposited in the Bragg peak, meaning that deeper tissues are largely spared a substantial radiation dose. This reduces the likelihood of side effects, which include an increased risk of cancer later in life. Medical imaging provides excellent knowledge of the internal anatomy of the body, allowing the dose distribution to be precisely predicted. However, patient movement, weight loss and shrinkage of the tumour mean that imaging is not always sufficient to determine the dose distribution delivered. In this talk, I will discuss the physical interactions of the proton beam with tissue, particularly concentrating on the possibility of measuring x-ray, gamma, optical and acoustic emissions so as to predict in real time the distribution of radiation dose to the body.

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30/01/2015 Simon Bevan/John Loizides

From Particles to Electronic Trading

We will give a detailed overview of the exciting world of FX electronic trading (eFX), detailing the cutting edge technology and mathematics that drive the modern markets. Throughout we will highlight how the skills developed during our stint in HEP translated directly into eFX and why particle physicists are still in such demand.

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