Particle Physics Phenomenology

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

Abstract

The particles called hadrons - e.g. the proton and neutron, of which atomic nuclei are composed - are actually made up of strongly interacting quarks and gluons (partons). A scattering process for a hadron is characterised in terms of two variables, x, the fraction of the momentum of the hadron carried by the parton and the energy scale of the process. Hadron interactions are described in terms of individual parton interactions and summed to give the total interaction rate. Parton interactions are calculable as an expansion in the QCD coupling constant, which becomes weaker at high energies. The make-up of the hadron in terms of partons cannot be directly calculated, but the variation with the energy scale can be if the scale is high enough for the coupling to be small. Hence one requires input parton distributions at low scales, which have to be extracted from experiment, then results of subsequent experiments with initial state hadrons can be predicted. A study of partons increases our knowledge of the proton and is an excellent test of QCD, and is also essential in searches for new particles. Much of current experimental particle physics involves hadron colliders, in particular the LHC at CERN which will hopefully for discover the final particle of the Standard Model, the Higgs boson, and also new physics. Understanding the LHC results to high accuracy and being able to disentangle the signs of new physics necessarily requires detailed knowledge of parton distributions and QCD interactions. One of the main parts of this project is obtaining partons from existing data and using theory, and developing the required theory. As well as finding the best parton distributions it is important to understand the uncertainties, both experimental and theoretical, on the processes calculated using partons at colliders, and this will be done at UCL. The theoretical uncertainty is the more difficult task, requiring a good understanding of the wide range of corrections that may be applicable to standard perturbative QCD. As the LHC obtains more data it will be compared to the theory, simultaneously improving our understanding of QCD and leading to improved predictions. At some point discrepancies between predictions and measurements will require a very detailed investigation of the significance of the discrepancy and the likelihood of it being a signal of new physics. One of the main candidates is the Higgs boson, and understanding partons will be instrumental in deciding if the Higgs boson has been discovered, and if so, determining its properties. Neutrinos are an all present yet elusive part of the Universe: More than fifty trillion neutrinos produced in the Sun pass through one's body per second without leaving a trace. They play an important role in most of the phenomena in the Universe, from the energy production in stars and supernova explosions to the general structure of galaxies. As such they currently provide the only solid departure from what is considered the Standard Model of particle physics and an explanation of their properties forms a crucial part of new theories that aim to understand the fundamental structure of nature. Because of their tiny masses, neutrino properties will be hard to detect at the LHC, but in new physics models there is often an interplay between predictions of neutrino properties and observations at the LHC. Given the role of neutrinos as a 'missing link' in our understanding and the potential of the LHC to provide completely new insights, this project aims to exploit the interplay between these two physics aspects to probe the fundamental laws of nature. The project therefore directly addresses the following question: What can we learn about fundamental models by combining LHC and neutrino data? Ultimately, it therefore aims to help in the understanding of the fundamental physics of nature.

Planned Impact

Both areas of Research at UCL have potential impact which will be summarised in turn. Let us begin with the Standard Model research. The extraction of the MSTW parton distribution functions, which quantitatively describe the manner in which the proton is made up of its constituent quarks and gluons, is led by Thorne. This has a variety of different areas of impact. Since it is one of the major pieces of information which goes into obtaining both the most likely values and the uncertainty on the rates of production of particles, both known and hypothesised, at particle colliders it has an impact on decisions on the energy at which these colliders should be run, when breaks should be taken, and indeed, whether colliders should be continued or switched off. As an example, the MSTW parton distribution functions were the single set which were used over the past two years to determine the limits on Higgs boson masses at the Tevatron collider at Fermilab, and to deduce what improvement in limits, or significance on signal could be found in the future. Similar reasoning is true for the reaction rates for ultra-high-energy neutrinos or other cosmic rays, so will impact on the considerations in planning the large scale detectors for these. Hence, the work at UCL will impact upon the nature of decision making in large-scale science projects, in particular the LHC in the next few years, in both the UK and worldwide.
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Additionally, the manner in which the proton (and neutron) are made up from quarks and gluons, and hence the details of the strong interaction force are also one of the fundamental questions of particle physics. As such the results of the MSTW analyses are likely to make their way into textbooks and the popular science literature as the best illustration of this particular, but rather fundamental aspect of physics. Indeed, Thorne is due to write the 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. The BSM physics research led by Deppisch also has significant potential impact. While neutrinos physics aspects have proven to be a major source of new discoveries, the public is not sufficiently aware of their importance. As neutrinos encompass a wide range of aspects such as particle physics, astrophysics and cosmology, they have the potential to play a key role in the public appreciation of physics research. There is the intention to undertake several measures to publicly communicate the research results in particular, and promote neutrino physics in general. This will include: (i) creation of a public internet blog, which will regularly inform on relevant physics developments; (ii) participation in university events such as open days, along with the creation of information materials; (iii) work with schools, offering class materials and presentations; (iv) collaboration on public outreach with H. Paes (U. of Dortmund), who will publish a popular science book on neutrino physics next year, which, in part, is based on past research with Deppisch. In addition, UCL has a wide range of training courses on public communication, and the intention is to use these to the fullest to enhance skills in public outreach. The planned development of a general software package for particle physics analysis by Deppisch is largely motivated by the desire to systematically assess the sensitivity and discriminative power of existing and planned experimental efforts with respect to fundamental physics searches. Such an assessment is a crucial step of the scientific decision making and steering process. As such it is expected to have an important impact in helping to influence recommendations for future particle physics efforts. This is especially topical given the current economic climate and funding situation, and would help to optimally distribute resources.

Publications

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Aguilar-Saavedra J (2012) Flavor in heavy neutrino searches at the LHC in Physical Review D

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Ball R (2013) Parton distribution benchmarking with LHC data in Journal of High Energy Physics

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Bertuzzo E (2017) Dark matter and exotic neutrino interactions in direct detection searches in Journal of High Energy Physics

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Butterworth J (2016) PDF4LHC recommendations for LHC Run II in Journal of Physics G: Nuclear and Particle Physics

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De Roeck A (2011) Structure functions in Progress in Particle and Nuclear Physics

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Deppisch F (2015) Neutrinos and LHC Physics in Acta Physica Polonica B

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Deppisch F (2015) Non-Standard Mechanisms for Neutrinoless Double Beta Decay in Physics Procedia

 
Description This grant involved a lot of 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. A lot of the work went towards developments which resulted in a new set of parton distributions, which appeared at the end of 2014. These MMHT2014 PDFs replaced the MSTW2008 parton distributions, which have been extensivley used at the LHC, including playing a central role in the discovery of the Higgs Boson. This grant has led to improvements in the theoretical framework in which the partons are extracted, particularly in the treatment of heavy quarks, the mathematical form of functions used to parameterise the partons, and in understanding the uncertainties on the distribution functions. There have also been investigations of the impact of the first LHC data to constrain PDFs, and work with other PDF groups to help understand differences in PDFs and the best ways to combine them in joint results.

Neutrinos are very difficult to detect but play an important role in most of the phenomena in the Universe, from the energy production in stars and supernova explosions to the general structure of galaxies. As such they currently provide the only solid departure from what is considered the Standard Model of particle physics and an explanation of their properties forms a crucial part of new theories that aim to understand the fundamental structure of nature. Because of their tiny masses, neutrino properties will be hard to detect at the LHC, but in new physics models there is often an interplay between predictions of neutrino properties and observations at the LHC. Using the role of neutrinos as a 'missing link' in our understanding and the potential of the LHC to provide completely new insights, the work within this grant has exploited the interplay between these two physics aspects to probe the fundamental laws of nature. The work has directly addressed the following question: What can we learn about fundamental models by combining LHC and neutrino data? Specifically, we have studied how observations of so called lepton flavour and number violating processes at the LHC can act as a crucial discriminator to distinguish between different models of neutrino masses. Most importantly, we have demonstrated that such searches at the LHC are complementary to searches for neutrinoless double beta decay, a nuclear process especially sensitive to the nature and size of neutrino masses. More generally, we have shown that the LHC can successfully search for lepton flavour violation, which provides crucial information on how the Standard Model can be extended. With the more obvious signs of beyond the Standard model physics at the LHC being elusive, more subtle tests such as these become ever more important. We also suggested a model that can explain a recent hint at the LHC for new physics. Another key finding was the demonstration that the observation of lepton number violating processes at the LHC would rule out a large class of models of baryogenesis (the mechanism explaining why we see matter in the universe). This is highly general statement that provides a deep connection between LHC physics, neutrino masses and the cosmology of the early universe.
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 culminatiated in the release of a new set of PDFs, the MMHT2014 PDFs. This was the first major update by our group since the MSTW2008 set. This new set is very widely used, and will probably be similar to the MSTW2008 set which resulted in one of the most cited papers in particle physics of the past few years.

The results on neutrino physics and Beyond the Standard Model Physics will aid in further theoretical developments and the planning of searches at the LHC and the planning for future neutrino experiments. Specifically, our findings on lepton flavour and number violation at the LHC provide a motivation to put a focus on these classes of processes in future LHC searches. Once new data from the LHC and from upcoming neutrino experiments will become available, the findings of our research will inform the next steps in determining new physics scenarios. The results also have implications on research and planning in cosmology and dark matter physics.
Sectors Education

URL https://mstwpdf.hepforge.org/
 
Description 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. 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. The results on neutrino physics and Beyond the Standard Model Physics have contributed to the theoretical developments and the planning of searches at the LHC and the planning for future neutrino experiments. Specifically, our findings on neutrinoless double beta decay have informed the experimental programme of the upcoming experiments SuperNEMO and SNO+.
First Year Of Impact 2011
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 IPPP Associateship
Amount £4,000 (GBP)
Organisation Durham University 
Department Institute for Particle Physics Phenomenology (IPPP)
Sector Academic/University
Country United Kingdom
Start 09/2011 
End 08/2012
 
Description IPPP Associateship
Amount £4,000 (GBP)
Organisation Durham University 
Department Institute for Particle Physics Phenomenology (IPPP)
Sector Academic/University
Country United Kingdom
Start 09/2012 
End 08/2013
 
Description IPPP Research Associateship
Amount £14,000 (GBP)
Organisation Durham University 
Department Institute for Particle Physics Phenomenology (IPPP)
Sector Academic/University
Country United Kingdom
Start 10/2009 
End 09/2013
 
Description IPPP Research Associateship
Amount £3,000 (GBP)
Organisation Durham University 
Department Institute for Particle Physics Phenomenology (IPPP)
Sector Academic/University
Country United Kingdom
Start 10/2013 
End 09/2014
 
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 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 Probing New Physics with SNO+ 
Organisation Queen Mary University of London
Country United Kingdom 
Sector Academic/University 
PI Contribution Providing theoretical guidance and input to the research project
Collaborator Contribution Development of experimental and analysis techniques to search for new physics at the upcoming neutrino experiment SNO+
Impact Influence on design of SNO+ experiment and its planned running and analysis
Start Year 2012
 
Description Probing New Physics with SNO+ 
Organisation University of Sussex
Country United Kingdom 
Sector Academic/University 
PI Contribution Providing theoretical guidance and input to the research project
Collaborator Contribution Development of experimental and analysis techniques to search for new physics at the upcoming neutrino experiment SNO+
Impact Influence on design of SNO+ experiment and its planned running and analysis
Start Year 2012
 
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 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