# Research at Glasgow

At Glasgow we perform world class research on the fundamental particles and their interactions. We are principally interested in phenomena that can be probed at current and next generation particle colliders, such as the Large Hadron Collider. We use our current model of particle physics, the Standard Model, to make predictions that can be tested by our experimental coleagues. We also examine models of exotic new physics beyond the Standard Model.

In particular, we focus on the behaviour of the strong force as described by Quantum Chromodynamics, both in perturbation theory and on the lattice; the physics of the Higgs boson; and models beyond the Standard Model such as supersymmetry, extra dimensions and little Higgs. Click on the links to the left for more details on individual topics, or continue below to read a basic introduction to the Standard Model.

# The Standard Model

The Standard Model of particle physics is at present our best theory for explaining how the universe works on a fundamental level. It describes the interactions of the fundamental particles via three of the four fundamental forces.

The particles themselves are divided into two
groups, *bosons* and *fermions*. The fermions (spin-half
particles) are "matter" particles that makes up the elements
around us, and are further divided into *quarks*
and *leptons*. The quarks are the constituents of the proton
and neutron, while the electron is an example of a lepton. The
bosons are sometimes refered to as the "force carriers" and are
responsible for the forces between particles. A force carrier is
exchanged between two particles, transfering momentum and
providing a force. The final particle is the Higgs boson, which is beleived to be
intimately linked to why particles have mass. The Higgs
boson is the only Standard model particle which has not been seen
in experiments. See the diagram for a summary of these particles.

The three forces described by the Standard Model are:

**Electromagnetism:**This force effects particle which have electric charge, such as the electron, and is responsible for both electricity and magnetism. In the Standard Model it is described by the theory of Quantum ElectroDynamics (QED), where the force is passed from one particle to another by exchanging a photon (a particle of light).

**The strong nuclear force:**This force is felt by particles which have "color" charge. It is responsible for holding together three quarks to form a proton or neutron. The proton consists of two up quarks and a down quark, while the neutron is two down quarks with an up quark. This force is mediated by the exchange of*gluons*and is described by the theory of Quantum ChromoDynamics (QCD).

**The weak nuclear force:**This force is not so apparent in everyday life as the other three. It is manifest in beta decays, for example, where a neatron decays to a proton, electron and neutrino. It is mediated by the exhange of W and Z bosons. This force is unusal because the W and Z bosons are rather heavy, making them difficult to produce and the force very short range. It is believed that the Higgs boson is linked to their mass, as explained by the Higgs mechanism of Electroweak Symmetry breaking, but this has not yet been experimentally confirmed.

The remaining force, the force of Gravity is absent from the Standard Model. It is much much weaker than the other three, and is not relevant to the interactions of particles at low energies.

# High Energy Colliders

In order to experimentally investigate these forces, machines have been built that accelerate particles to ever-higher energies and then collide them together. Such high-energy colliders are able to produce the fundamental particles and study their interactions, testing the Standard Model. Until recently, the highest energy achieved was at the Tevatron collider at Fermilab (just outside Chicago, USA), which accelerates protons and anti-protons to energies of almost 1000 times their rest mass.

These energies were surpassed when the Large Hadron Collider (LHC) (at CERN in Geneva, Switzerland) began operation in 2009. Data was initially taken at a total energy of 7 TeV. Now the collider is being upgraded and will soon turn on at energies or 13 TeV, possibly increasing to 14 TeV. With such an increase in energy, it is hoped that the LHC will help solve various problems that have arisen with the SM.

In particular, on July 4 2012, CERN announced the discovery of the Higgs boson which confirms the mechanism for providing masses to the fundamental particles and is the last particle of the SM to tbe found. Although the Higgs boson decays almost instantaneously, it can be detected by observing its decay into other SM particles. This means that its dicovery and the search for furth new particles depend heavily on theoretical predictions in order to disentangle signals for new physics from large backgrounds predicted by the SM.

# Recent student theses

- António Morais, 2013, supervisor Dr D. Miller

Grand Unification Phenomenology at the LHC and Beyond

- Daniel Coumbe, 2013, supervisor Dr J. Laiho

Exploring a Formulation of Lattice Quantum Gravity

- Gordon Donald, 2013, supervisor Prof. C. Davies

Semileptonic and radiative meson decays from lattice QCD with improved staggered fermions

- Iain Kendall, 2010, supervisor Prof. C. Davies

Lattice QCD studies of Upsilon physics

- Luo Rui, 2010, supervisor Dr D. Miller

Neutrino masses and Baryogenesis via Leptogenesis in the Exceptional Supersymmetric Standard Model

- Peter Ahron, PhD, 2008, supervisor Dr David J. Miller

Aspects of Electroweak Symmetry Breaking in Physics Beyond the Standard Model

- David Thomson, PhD, 2008, supervisor Prof. C. Froggatt

Low Energy Consequences of some Non-standard Higgs Models

- Ian Allison, PhD, 2006, supervisor Prof. C. Davies

Dynamical lattice QCD determinations for heavy quark physics

- Greig Cowan, PhD, 2005, supervisor Dr M. Alford

Single-Colour and Single-Flavour Colour Superconductivity

- Jack Cheyne, PhD, 2005, supervisor Dr M. Alford

Colour Superconductivity and steps beyond the mean field approximation

- Alan Gray, PhD, 2003, supervisor Prof. C. Davies

Upsilon Spectroscopy and Leptonic Decays using Fully Unquenched Lattice QCD

won Ogden prize 2004 for best UK PhD in particle physics phenomenology

- Josef Dubicki, PhD, 2002, supervisor Prof. C. Froggatt

Renormalization Group Study of Four Generation Models

- Laurence Marcantonio, PhD, 2001, supervisor Prof. C. Davies

Unquenched Lattice Upsilon Spectroscopy

- Alessandro Tiesi, PhD, supervisors Prof. C. Froggatt and Dr. A. Davies

Higgs boson masses in a Non-Minimal Supersymmetric Model

- Gordon Aird, PhD, 2000, supervisor Dr. A. Watt

Modelling the Induced Magnetic Signature of Naval Vessels

- Alessandro Usai, PhD, 2000, supervisor Dr. A. Davies

Spontaneous CP violation in the Next-to-Minimal Supersymmetric Standard Model

- Mark Gibson, PhD, 1999, supervisor Prof. C. Froggatt

The Scalar and Neutrino Sectors of the Anti-Grand Unification Theory and Related Abelian Models

- Nektarios Psycharis, PhD, 1999, supervisor Dr. I. Barbour

Analysis of the Lee-Yang Zeros in Lattice Compact QED with Scalars and Fermions in 3D and in Lattice Non-Compact QED in 4D

- Gordon Jenkins, PhD, 1997, supervisor Dr. A. Davies

Electroweak Baryogenesis in Two Higgs Models

- Mark Campbell, MSc (by research), 1997, supervisor Dr. S. Collins

A Study of D-State Upsilon Spectroscopy Using Lattice QCD

- Paul McCallum, PhD, 1997, supervisor Dr. C. Davies

Upsilon Spectroscopy using Lattice QCD

- Susan Morrison, PhD, 1997, supervisor Dr. I. Barbour,

Lattice QCD at Finite Baryon Density with an Implementation of Dynamical Fermions