Theory Consolidated Grant. - Standard Model Phenomenology and Beyond the Standard Model Phenomenology.

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

The main focus of Hamilton's research is to further develop precise computer simulations based on QCD calculations (so-called Monte Carlo techniques) for the large number of final state particles in collider physics processes. This will facilitate discovery and interpretation of new physics at the Large Hadron Collider (LHC). While precision simulations may not always be needed to claim a discovery, e.g. if new physics reveals itself as a heavy, easily resolved new particle, in many scenarios, such as supersymmetry, signals are expected to manifest as subtle distortions in the shapes of distributions. Hence, an accurate understanding of the Standard Model background, subject to all experimental cuts, is fundamental to claiming a discovery, or setting exclusion limits. Moreover, precise simulations are essential in attempting to determine what it is that has been found. The newly discovered 125 GeV mass Higgs-like boson is a prime example of this, and one for which simulations that Hamilton contributes to are being used to this end by the LHC Higgs working group. Research in the near future will focus on improved precision and theoretical rigour for the Monte Carlo generators used in simulations.

Thorne's work is complementary and in many senses similar. It involves the details of the initial state in particle collisions. At colliders which use hadrons, e.g. the LHC which uses protons, the beam is effectively made up of the hadronic constituents, quarks and gluons, generically known as partons. Hence, in order to make predictions for any reaction, both for Standard Model and new physics, one needs to know the precise partonic composition of the hadrons in terms of both the energy fraction of the hadron and the energy scale of the scattering process (e.g., the mass of a particle produced). Thorne is the lead member of the MSTW group that provides one of the standard sets of parton distribution functions (PDFs) used in both the experimental and theoretical analyses at the LHC and previous colliders. The technique is constantly being improved in terms of the theoretical basis, and more data are appearing which help constrain the PDFs further. Hence, Thorne's work will be based on improving PDF determination, providing updated PDFs for use at colliders and helping to determine the consequences of any changes in both central values and uncertainties. Both Hamilton and Thorne are involved in precision calculations at the LHC and will provide expertise in interpreting any deviations which could be the first sign of Beyond the Standard Model (BSM) Physics.

BSM phenomenology aims to uncover deeper laws and structures in nature than currently known. The work of Deppisch achieves this by taking experimental results (e.g. from the LHC) and comparing them with predictions derived from new theoretical ideas (e.g. the notion of more than three space dimensions). Neutrinos play a very important role as they are the least understood of all known matter particles. Their most mysterious property is their lightness; the exact value of the mass is unknown but it is at least a million times smaller than the next lightest particle, the electron. There is no agreed explanation for this huge discrepancy which goes at the heart of the fundamental question: What is mass? Even if the Higgs boson is confirmed by the LHC as the source of the mass of particles such as quarks, the lightness of neutrinos still remains a mystery, but we also expect that once we solve this, a large piece of the puzzle of nature will fall in our lap. The proposed research aims to determine the absolute neutrino mass as precisely and robustly as possible from a range of experimental results which are expected over the next years. In addition, the work will correlate physics phenomena at different experiments within a theoretical framework. This is necessary as no single experiment can probe all aspects of nature.

Planned Impact

We begin with the impact of the Standard Model research. The extraction of the MSTW parton distribution functions (PDFs) impacts in a variety of areas. PDFs are a major piece of information required for obtaining both the central values and uncertainties on the rates of particle production at colliders. Naturally, therefore, they impact on decisions concerning the energy at which colliders should be run, when breaks should be taken, and indeed, whether they should be continued or switched off. The MSTW PDFs were the single set used to determine the limits on Higgs boson masses and significance of excesses at the Tevatron collider at Fermilab, and to deduce what improvement in limits/signal significance could be reached with future running. Parton luminosity plots provided by the MSTW collaboration are one of the standard pieces of summary information used in meetings for future planning. Similar reasoning is true for the reaction rates for ultra-high-energy neutrinos or other cosmic rays, so PDFs will impact on the planning of large scale detectors for these. Additionally, the manner in which the proton is comprised of quarks and gluons is one of the fundamental results of particle physics. As such, the results of the MSTW analyses are likely to make their way into textbooks and popular science literature as a standard illustration of this particular aspect of physics. Indeed, Thorne is due (after some delays) to write an article describing this physics for the peer-reviewed version of Wikipedia, known as Scholarpedia, so the default online source for the account of this subject will be extremely directly influenced by the work, and will be periodically updated as important new results are found. Naturally, as with the PDFs, besides theoretical and phenomenological studies, Monte Carlo event generators have an important role to play in the planning and design of future experiments, and in determining the way in which existing experiments are commissioned and run. Indeed, prominent documents on these subjects, such as the ATLAS technical design report, are heavily comprised of simulation-based studies. The design and physics programs of current and future experiments, most notably the LHC, will therefore be directly influenced by the tools developed by Hamilton and collaborators, e.g. the Herwig++ and Powheg-Box packages. Hence, Standard Model work at UCL will impact upon decision making in large-scale science projects in both the UK and worldwide.

Being a part of fundamental research, the Standard Model and particularly the Beyond-the-Standard-Model (BSM) phenomenology research serves the purpose of deepening human knowledge of the fundamental properties of nature beyond the current understanding, and is therefore beneficial to the general public. Such fundamental research is especially attractive to young people, and can serve as a gateway to enter a career in science, technology, engineering or mathematics, areas that are vital to the economy. This effect will occur both indirectly by disseminating the research results of the project to the wider public, as well as directly by training students who may choose careers outside fundamental research. The specific BSM research proposed here is performed in collaboration with experimental colleagues of the neutrinoless double beta decay experiments SuperNEMO and SNO+ supported in the UK, and its aim is to clearly understand the impact of ongoing and future experiments on fundamental theories. It therefore helps in evaluating the benefit of experiments with regard to their costs, which is necessary for science policy-making agencies both at national and international level. Future experimental efforts are directly assessed by similarly determining the impact of planned or hypothetical experiments on the physics results that can be extracted. This will prove helpful as well for science policy-making agencies when deciding on the composition of future experimental efforts.

Publications

10 25 50
 
Description This grant involves work on parton distributions, which describe the manner in which the proton is made up of constituent quarks and gluons, generically known as partons. This is necessary to understand how the partons interact to form other particles when protons are collided at high energy, e.g. at the LHC (Large Hadron Collider) in CERN and any future hadron colliders. A lot of the work goes towards developments which will ultimately go into a new set of parton distributions, incorporating more LHC data in the constraints. There has also been investigations on the relationship between PDFs and the strong coupling constant and masses of the quarks, as well as the impact of final HERA collider data on constraining PDFs. Results from this and also so far from including new LHC data show good compatability with data, and in little change in the PDFs other than a slight reduction in their uncertainty. Also there has been work withother PDF groups to help understand differences in PDFs and the best ways to combine them in joint results. A new recommendation for combining PDFs has recently been published which is becoming fairly standard usage at the LHC, particularly for studies of the Higgs boson. More recent studies have also highlighted the necessity for understanding correlated systematic uncertainties at LHC experiments given the high statistical precision now being reached.

In the course of this grant we have also carried out work to further enhance what was already the world's most accurate Monte Carlo simulation of Higgs boson production in LHC collisions (co-developed by UCL, Milan and Oxford). This upgraded program is being intensively used to confront LHC measurements with Standard Model
theory, by experimentalists within the LHC collaborations. Significant progress has also been made in generalising the theoretical underpinnings of the latter simulation, such that they can be applied to a much wider range of LHC particle production processes.

Within non-Standard Model physics, among our main findings is the result that it is possible to rule out a large number of baryogenesis models by observing certain processes at the LHC or in radioactive decays. Baryogenesis models try to explain why there is so much matter in the Universe as we observe (we would otherwise expect it had annihilated with antimatter in the early Universe). These results provide a direct and highly model-independent connection between experiment and the matter-antimatter asymmetry puzzle which is very difficult to probe otherwise.

We have also interpreted many of the hints of new physics at the LHC that have been seen in 2014-16, in the light of models that incorporate a mechanism to explain why neutrinos are so light. In this regard, our work has been at the forefront connecting the latest LHC results with the distant neutrino sector. Furthermore, we have discovered two novel scenarios that can potentially connect the origin of the neutrino masses with the origin of Dark Matter, and we also started a program to use Dark Matter experiments as constraints on neutrino properties.

Starting a program on the interface between nuclear and particle physics, we were first to comprehensively determine the constraints on neutrinoless double beta decay from standard nuclear beta decays. Neutrinoless double beta decay is an exotic, hypothetical radioactive nuclear decay that has immense importance for searches for physics beyond the Standard Model.
Exploitation Route The determination of parton distributions is always improving, so we, and others have developed the work in this grant to take things further and improve our understanding of partons. The developments on parton distributions within this grant, have been used extensively at the LHC and other experiments, and by the theory community.
The work within the grant recently culminated in the release of a new set of PDFs. This was the first major update by our group since the MSTW2008 set. This new set is becoming very widely used. The MSTW2008 set resulted in one of the most cited papers in particle physics of the past few years, and there are already well over 500 citations
for this new set of PDFs, and it is being used in a multitude of studies at the LHC.

The findings relating to the work on Monte Carlo event simulation are being taken forward by applying the new general formalism developed there to other particle production processes at the LHC (besides that of the Higgs boson). Specifically, this work is now being carried forward by senior staff members in the CERN theoretical physics group and elsewhere. The latter developments are readily applicable to so-called `Standard Candle' LHC processes like W and Z gauge boson production, yielding increased precision in the description of these processes, which are also typically troublesome backgrounds in searches for new particles. More generally, and more broadly speaking, the findings resulting from this work are manifested in free, publicly availble, computer programs, which are, in some cases, being heavily used by experimental physicists in interpreting LHC data.

In BSM physics, several colleagues have expressed an interest to attempt to use our general approach of falsifying classes of scenarios using observations rather than analyzing each scenario one by one. More specifically, several groups are exploring extensions of our work to find more precise criteria. We have collaborated and interacted with several colleagues outside this working group which have been exploring our findings in novel directions, and they will continue to do so.

On a similar but broader front, our recent review of neutrino mass models and their phenomenology at the LHC has already collected over 120 citations at the time of writing. It provides a comprehensive update on the various model parameter limits which has been used as a basis for several follow-up analyses and summaries of our findings were presented in several conference plenary talks by other speakers.

Our comprehensive analysis of the apparent reduction of the axial vector coupling in nuclear beta decays, together with a leading nuclear physics theory group, has important consequences for searches for 0vbb. It is being used by experimental groups to assess the sensitivity of current and future 0vbb experiments.
Sectors Education

URL http://www.hep.ucl.ac.uk/mmht/index.shtml
 
Description The determination of parton distributions is always improving, so within this grant we have taken things further and improved our understanding of partons. The developments on parton distributions within this grant, have been used extensively at the LHC and other experiments, and by the theory community. The updated set of PDFs, MMHT2014, have garnered over 500 citations so far. Some of our developments in PDF studies have impacted the updated studies by other groups. The work on comparing and combining PDFs is also widely used at the LHC as there is an increasing desire to utilise the results from a variety of the best groups in as useful a manner as possible. A recent new recommendation for combining PDFs is being used as a standard reference in LHC studies, particularly for studies of the recently discovered Higgs Boson, and has garnered over 350 citations. The Monte Carlo simulations co-developed by the UCL group are very widely used by LHC experimentalists. Arguably the two most important applications are, i) confrontation of experimental measurements with Standard Model theoretical predictions, most prominently our NNLO state-of-the-art simulation of Higgs boson production, and ii) the experimental calibration of jets, which are ubiquituous in essentially all LHC collisions. Our analyses of various LHC excesses in 2014-16 have collected over 260 citations. This includes the first interpretation of the CMS eejj excess. Altogether, our findings have motivated several follow-up analyses. Summaries of our findings were presented in several conference plenary talks by other speakers. Our work has been in the context of models that incorporate mechanisms to explain the lightness of neutrinos, and our results are at the forefront of connecting LHC data with the neutrino puzzle. Our findings that models of baryogenesis can be falsified from observing lepton number violating processes at the LHC or neutrinoless double beta (0vbb) decay provide a strong model-agnostic connection between experiment and the puzzle of matter-antimatter asymmetry. They have for example been used by experimental collaborations searching for 0vbb to further strengthen their physics case. Summaries of our findings were presented in several conference plenary talks by other speakers. More specifically, our work on a possible connection of the Dark Matter and neutrino masses has motivated a recent PhD graduate to apply for a fellowship at UCL with a research proposal that plans to extend our work. Starting a research program on the applicability of techniques used in particle theory on recent approaches to artificial intelligence (deep machine learning), our initial results have already been used to improve algorithms for large crowd simulations for the company eurosimtec GmbH.
First Year Of Impact 2014
Sector Education
Impact Types Societal

 
Description Chinese Scholarship Council Studentship
Amount £64,000 (GBP)
Organisation Chinese Scholarshop Council 
Sector Academic/University
Country China
Start 10/2016 
End 09/2020
 
Description Exchanges
Amount £12,000 (GBP)
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 03/2017 
End 02/2019
 
Description Impact Accelerator Award
Amount £5,000 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 10/2015 
End 12/2015
 
Description Royal Society International Exchanges
Amount £6,000 (GBP)
Funding ID IE130084 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 12/2013 
End 12/2014
 
Description STFC Support for Short Courses and Summer Schools
Amount £70,000 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 03/2017 
End 09/2017
 
Description UCL Studentship
Amount £50,000 (GBP)
Organisation University College London 
Sector Academic/University
Country United Kingdom
Start 10/2014 
End 09/2017
 
Description Visiting Professorship
Amount £5,000 (GBP)
Organisation Physical Research Laboratory 
Sector Academic/University
Country India
Start 02/2016 
End 03/2016
 
Description Exploring the Terauniverse with the LHC, Astrophysics, and Cosmology 
Organisation European Organization for Nuclear Research (CERN)
Country Switzerland 
Sector Public 
PI Contribution One of the nodes for this ERC grant
Collaborator Contribution The other nodes. CERN is the central node.
Impact A continuous interaction, and two 2-year RA positions and a PhD student for UCL
Start Year 2011
 
Description Exploring the Terauniverse with the LHC, Astrophysics, and Cosmology 
Organisation Imperial College London
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution One of the nodes for this ERC grant
Collaborator Contribution The other nodes. CERN is the central node.
Impact A continuous interaction, and two 2-year RA positions and a PhD student for UCL
Start Year 2011
 
Description Exploring the Terauniverse with the LHC, Astrophysics, and Cosmology 
Organisation King's College London
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution One of the nodes for this ERC grant
Collaborator Contribution The other nodes. CERN is the central node.
Impact A continuous interaction, and two 2-year RA positions and a PhD student for UCL
Start Year 2011
 
Description MSTW/MMHT 
Organisation Durham University
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution The main coordinater and one of the most active working participants in a four-person collaboration.
Collaborator Contribution Part of a four person collaboration on a project.
Impact Publications of MSTW parton distributions which are a default in analyses at the LHC and Tevatron particle colliders.
Start Year 2006
 
Description MSTW/MMHT 
Organisation European Organization for Nuclear Research (CERN)
Department Theoretical Physics Unit
Country Switzerland 
Sector Academic/University 
PI Contribution The main coordinater and one of the most active working participants in a four-person collaboration.
Collaborator Contribution Part of a four person collaboration on a project.
Impact Publications of MSTW parton distributions which are a default in analyses at the LHC and Tevatron particle colliders.
Start Year 2006
 
Description MSTW/MMHT 
Organisation University of Cambridge
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution The main coordinater and one of the most active working participants in a four-person collaboration.
Collaborator Contribution Part of a four person collaboration on a project.
Impact Publications of MSTW parton distributions which are a default in analyses at the LHC and Tevatron particle colliders.
Start Year 2006
 
Description Models with and without Lepton and Baryon Number Violation 
Organisation Physical Research Laboratory
Country India 
Sector Academic/University 
PI Contribution Development of models and performing calculations
Collaborator Contribution Development of models and performing calculations
Impact Several publications
Start Year 2013
 
Description PDF4LHC 
Organisation Deutsches Electronen-Synchrotron (DESY)
Country Germany 
Sector Academic/University 
PI Contribution I am a member of the steering committee and one of the main contributors to a working group on PDFs for the LHC
Collaborator Contribution Many other collaborators about 5 of whom are also steering committee members and main contributors.
Impact Numerous PDF4LHC reports and recommendations for using PDFs at the LHC which are widely adopted by the experiments.
Start Year 2008
 
Description PDF4LHC 
Organisation European Organization for Nuclear Research (CERN)
Country Switzerland 
Sector Public 
PI Contribution I am a member of the steering committee and one of the main contributors to a working group on PDFs for the LHC
Collaborator Contribution Many other collaborators about 5 of whom are also steering committee members and main contributors.
Impact Numerous PDF4LHC reports and recommendations for using PDFs at the LHC which are widely adopted by the experiments.
Start Year 2008
 
Description PDF4LHC 
Organisation Michigan State University
Country United States 
Sector Academic/University 
PI Contribution I am a member of the steering committee and one of the main contributors to a working group on PDFs for the LHC
Collaborator Contribution Many other collaborators about 5 of whom are also steering committee members and main contributors.
Impact Numerous PDF4LHC reports and recommendations for using PDFs at the LHC which are widely adopted by the experiments.
Start Year 2008
 
Description PDF4LHC 
Organisation National Institute for Nuclear Physics
Country Italy 
Sector Academic/University 
PI Contribution I am a member of the steering committee and one of the main contributors to a working group on PDFs for the LHC
Collaborator Contribution Many other collaborators about 5 of whom are also steering committee members and main contributors.
Impact Numerous PDF4LHC reports and recommendations for using PDFs at the LHC which are widely adopted by the experiments.
Start Year 2008
 
Description PDF4LHC 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution I am a member of the steering committee and one of the main contributors to a working group on PDFs for the LHC
Collaborator Contribution Many other collaborators about 5 of whom are also steering committee members and main contributors.
Impact Numerous PDF4LHC reports and recommendations for using PDFs at the LHC which are widely adopted by the experiments.
Start Year 2008
 
Description Quenching of Nuclear Matrix Element Operators 
Organisation Yale University
Department Department of Physics
Country United States 
Sector Academic/University 
PI Contribution Particle Physics expertise
Collaborator Contribution Nuclear Physics expertise
Impact Particle and Nuclear Physics
Start Year 2017
 
Description South-East Particle Theory Alliance 
Organisation Royal Holloway, University of London
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution Joint Research
Collaborator Contribution Joint Research
Impact N/A
Start Year 2017
 
Description South-East Particle Theory Alliance 
Organisation University of Sussex
Country United Kingdom 
Sector Academic/University 
PI Contribution Joint Research
Collaborator Contribution Joint Research
Impact N/A
Start Year 2017
 
Description Systematic Treatment of Effective Operators in Neutrinoless Double Beta Decay 
Organisation University of Jyvaskyla
Country Finland 
Sector Academic/University 
PI Contribution The collaboration was initiated by me and I am responsible for the particle physics part of the collaboration. I am also doing the the major part of the analysis required for the project work.
Collaborator Contribution Prof. Suhonen (partner) provides the computational framework for calculating the nuclear matrix element of the process considered. He consults on the nuclear physics details to inform the analysis.
Impact First paper expected to be published by the end of the year 2014
Start Year 2013
 
Description Open Day and Panel Discussion (India) 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Participated in 4 day long open-day event at PRL Ahmedabad India, especially in two panel discussion and Q&A sessions on physics research and teaching addressing about 400 school students, undergrad students, the general public and media, which sparked questions and discussions afterwards
Year(s) Of Engagement Activity 2016
 
Description Outreach Talk North London Collegiate School 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact talk sparked questions and discussion afterwards; motivated students to apply at UCL

Asked to participate in South England wide teachers' education event
Year(s) Of Engagement Activity 2014