University of Edinburgh
Collider Physics
The next five years will be a decisive time for the future of fundamental physics. When data starts to flow from LHC it should soon become clear whether there is a Higgs boson, supersymmetry, a new strongly-coupled theory, or even extra dimensions; or whether we have to redouble our efforts to understand overwhelming backgrounds in order to uncover these novel phenomena. There will also be more data on bottom and top quarks than ever before, and thus new opportunities for uncovering clues for new physics in the flavour sector. This will be the Golden Age for our generation of physicists, and we don't intend to miss it.
Higgs Phenomenology
R.D. Ball, E. Gardi
The search for Higgs particles is one of the central issues at the Tevatron and at the LHC. Our research in this area is focussed on improving cross-section predictions for signal and background processes, needed to fully exploit the discovery potential of the LHC. Our studies include, for example, Higgs decay into two photons which is the main detection channel for a light Higgs Boson in the Standard Model.
Very often precise prediction require all-order resummation of the dominant radiative corrections owing to multiple soft gluon emission. Such resummed computations are available today only for simple inclusive cross sections. Our main goal is to develop means for resummation in a wider class of observables, ones that include jets and final state cuts as needed for the physics analysis at the LHC.
Additional work focusses on exploring the prospects for Higgs physics at future e+e- linear and photon colliders as well as the physics of heavy Higgs resonances which have to be treated using non-perturbative methods.
Infrared singularities in QCD amplitudes
R.D. Ball, E. Gardi, A.D. Kennedy
We are leading a major effort aimed at understanding the infrared singularities of QCD amplitudes. On-shell scattering amplitudes in massless gauge theories are characterised by soft and collinear singularities. Studying the structure of these singularities is important both from a theoretical perspective, and from the pragmatic one of collider phenomenology. Infrared singularities provide the key to soft-gluon resummation, which is essential for precise predictions. Another long-term goal is to develop a general procedure for combining real and virtual contributions at the multi-loop level.
Perturbative QCD: higher-order corrections and resummation
R.D. Ball, E. Gardi, A. Berera, J. Smillie
A detailed understanding of QCD processes at high-energy colliders is essential for reliable background estimates in new particle searches. There is an ever pressing demand for the calculation of next-to-next-to-leading-oder (NNLO) corrections and the resummation of large logarithmic corrections.
We are currently working on the calculation of radiative corrections to two-gluon induced processes. This include, in particular, two-loop computations of 2-> 2 scattering processes. Another important goal is to combine fixed-order calculations with a summation of soft and collinear gluon radiation.
Many high energy processes involve more than one hard scale, the paradigm for such processes being inclusive hard cross-sections at small x in deep inelastic scattering. Now that we know how to resum leading and next-to-leading small-x logarithms in DIS, we want to apply these resummations to predictions at hadronic colliders. Recently we have computed resummed cross-sections for Drell-Yan processes (including vector boson production), heavy quark production and Higgs production, and we hope soon to also resum inclusive jet cross-sections. There is an important interplay between high energy resummation and threshold (Sudakov) resummation which we aim to develop further. Phenomenological implications of both types of resummation will be developed through their inclusion in the NNPDF programme. We are also studying the implications of resummation on the scattering of ultra high energy cosmic rays.
Parton Distribution Functions
R.D. Ball, L. Del Debbio
As part of an international software development project, NNPDF, we have developed a neural-network method to parametrise Parton Distribution Functions, crucial for understanding physics at hadron colliders without systematic theoretical bias. We recently completed a determination of PDFs from DIS data, and inclusion of hadronic data will follow soon. We expect this work to provide a full set of global PDFs with realistic errors, in time for the first analyses of LHC data. Conversely, results from the LHC will be used to improve the determination of the PDFs. We plan improvements in the treatment of heavy quarks, the inclusion of threshold and Sudakov resummation, and high energy resummation. This is a major project with a long term future.