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.

Standard Model 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

Aerial view of CERN and surroundings

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.

The Standard Model
Click to enlarge

Recent student theses