Lattice QCD and the Standard Model of Particle Physics

We shall carry out calculations using Quantum ChromoDynamics to study the forces
that bind quarks into observable particles known as hadrons.

The key aim of this project is to improve our understanding of the Standard
Model including Quantum Chromodynamics (QCD) which describes how quarks are held
together inside nuclei. Quarks are never seen as free particles, so that
experimental information can only be obtained from the study of bound states of
quarks, known as hadrons. The aim is to solve QCD in the context of the
Standard model more accurately, so we can connect the fundamental properties of
quarks to the experimental information gained from hadrons, notably from the
Large Hadron Collider at CERN. Numerical methods known as lattice QCD are a
precision tool in this endeavour.

The Standard Model of particle physics unifies three forces of nature: the weak,
electromagnetic and strong forces. Except for gravity the Standard Model is
extraordinarily successful in accurately predicting the outcome of experiments
and includes the theory of electromagnetism, atomic physics, the forces that
bind nucleons in the nucleus and radioactive decay. At the LHC the Standard
Model is being tested to extreme levels and, in particular, in high energy
processes where any inadequacy of the model is most likely to be detected. This
centres partly on the existence or not of the Higgs particle but if there is any
physics "beyond the Standard Model" (BSM) a signal will be found in the
disagreement between experimental measurements of particular processes and
theoretical prediction based on the Standard Model alone. Any discrepancy is
likely to be small but must ultimately be resolved by new BSM physics. It is
crucial, therefore, to develop calculational techniques that can reliably and
accurately compute predictions for these processes.

We will use the new DiRAC phase-2 supercomputer and especially the Tightly
Coupled Cluster (TCC) part in the HPCs in Cambridge to carry out intensive
calculations using lattice QCD. In particular, some properties of particles
containing at least one heavy quark (in practice the b or c quark) are very
sensitive to the fine details of the Standard Model, and we have developed
special techniques for studying these properties on a space-time lattice. We are
part of the UKQCD national consortium and also of the HPQCD international
collaboration (www.physics.gla.ac.uk/HPQCD) and will use lattice techniques
which allow us to carry out ab-initio calculations with good control over
systematic and statistical errors enabling us in some cases to predict
observable quantities to within 1% total error.

For example, the properties of interest that are a stringent test of the
Standard Model are the decays of B mesons which are mesons containing one b
quark and one light, u or d, quark, and of Bs where the u or d quark is replaced
by a strange quark. These decays will be measured in the LHCb experiment at the
CERN LHC.

Our work brings together research done by many theorists and experimentalists to
carefully probe physics at high energies and to search for BSM physics.

Pathways to Impact are as agreed at a meeting on 21st November 2011