Physicists are using supercomputers to simulate the forces that bind quarks inside protons and neutrons, aiming to predict particle behaviour with better than 1% precision. The Standard Model of particle physics is the most successful theory ever devised, but it is incomplete. Any crack in its predictions—a tiny mismatch between theory and experiment—could reveal entirely new forces or particles. The problem is that quarks are never seen alone; they are always locked inside composite particles called hadrons. To test the Standard Model, researchers must connect what they measure in experiments—like those at the Large Hadron Collider—to the fundamental properties of quarks. This project uses lattice quantum chromodynamics, a numerical method that simulates quark interactions on a four-dimensional grid of spacetime, to make those connections far more accurate than before. If successful, this work will sharpen the search for physics beyond the Standard Model. When LHC experiments measure rare decays of B mesons, theorists will know whether any discrepancy is a genuine signal of new physics or just a calculational error. This is fundamental science: it will not directly change a manufacturing process or a medical scan tomorrow. But past fundamental research into particle physics gave us the World Wide Web, medical imaging, and the transistors in every smartphone. A deeper understanding of nature’s basic forces is the raw material for future technologies no one has yet imagined.
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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.
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