Theoretical Particle Physics Rolling Grant

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

Abstract

In order to reach the highest possible energies, the current particle colliders, the DESY electron-positron collider at Hamburg (which finished running in 2007, but from which data are continuing to appear) and the Tevatron proton-antiproton collider near Chicago, use protons as at least one of their colliding particles. Protons are particles which interact via the strong force, and are composite particles because the strong force binds the fundamental constituents, partons - which may be quarks or gluons. The collider due to turn on at CERN, the Large Hadron Collider (LHC), will be a proton-proton collider. The LHC will achieve the highest energies at a particle collider by a factor of more than 7, and will enable us to see if the missing particle within the Standard Model of particle physics, the Higgs boson, exists - as well as to detect the first signs of physics beyond the Standard Model, for example Supersymmetry, where each Standard Model particle has a supersymmetric partner. At low energies we think of the partons as being bound within the proton, but at very high energies the strong coupling becomes weaker, and the interactions of colliding protons can be thought of as interactions between the partons in each proton, which may be calculated as an expansion in the strong coupling constant. Hence, in order to understand the results of any hadron collider experiments one must first understand how the proton is made up out of its partonic constituents. To a certain degree this can be calculated, but the strong coupling makes some expansions badly defined, and some of the information must be determined by comparison with experimental data. Therefore, one must perform enough independent experiments, and use the theoretical calculations within the theory of the strong force (Quantum ChromoDynamics - QCD) as accurately as possible, to determine the composition of the proton in terms of the gluons and the six flavours of quark (up, down, strange, charm, bottom and top). This requires the use of data from a variety of experiments, and it must be checked that all pieces of data are consistent with the partons and the QCD theory, hence testing QCD to great accuracy, and measuring the strong coupling. Once a consistent set of parton distributions is determined, these partons may be used to predict any other process using the protons. This can be the production of beyond the Standard Model particles, or for Standard Model processes, where the latter often mask the former. The project proposed is to improve the determination of parton distributions and their consequences for collider physics. This will be achieved by incorporating new theoretical calculations, e.g. higher order in the coupling or more precise inclusion of heavy particle corrections, and also by the inclusion of data on new processes, both from the existing colliders and from the forthcoming LHC. These new theoretical developments and the new influx of data will mean we require a lot of effort to obtain the best partons. However, this is essential if the data are to be interpreted properly, and hence, if we are to increase our understanding of the Standard Model and also to search for the physics beyond it. It is very likely that any signal for new physics at the LHC will initially be ambiguous, since it could be due to an uncertainty in our understanding of the Standard Model, in particular strong interaction physics and parton distributions, and this has previously occurred at other hadron colliders. The group at UCL has the precise expertise to disentangle these possibilities due to both the experience in analysing numerous different types of data sets in comparison to predictions, and in developing improvements to the theoretical framework. In the case that a new signal is observed, the group will aim to help interpret precisely what it signifies, where again the ability to separate it out from the background will be vital.

Publications

10 25 50
 
Description This grant resulted in improvements to a new set of 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. Work mainly from this grant resulted in the improvement of a new set of parton distributions which incresead our knowledge of the proton and enabled much of the study at the LHC to proceed optimally.The improvements were primarilyt in the area of understanding of the role of the strong coupling of Quantum Chromodynamics and of the mass of heavt quarks (the charm and beauty quarks) in the theoretical understanding of the partons.

In this grant some work was also done specifically on the role of parton distributions and the strong interaction in producing Higgs particles. Also there was some work on how signs of lepton flavour violation (e.g. electrons converted to
muons) could be a sign of physics beyond the standard model and of help in understanding neutrinos.
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 parton distributions themselves, called MSTW2008, were improved by work in this grant, and these improvements have been used extensively at the LHC and other experiments, and by the theory community.
Sectors Education

URL https://mstwpdf.hepforge.org/
 
Description The description 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 parton distributions themselves, called MSTW2008, and the improvements made within this grant, have been used extensively at the LHC and other experiments, and by the theory community. The specific resulst on Higgs physics impacted the manner in which the Higgs particle was searched for at the LHC and Tevatron, and the additional work on lepton flavour violation influenced plans and studies in neutrino and beyond the standard model physics.
First Year Of Impact 2010
Sector Education
Impact Types Societal

 
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 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 An ongoing 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 An ongoing 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 An ongoing 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 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