Quark, strangeness, and charm

Quarks are strange and equally charming, but all attempts to observe them in isolation would be in vain. Now, particle physicists are embarking on a new attempt to solve the mysteries of quarks with the completion of the three most powerful supercomputers ever applied to this problem. One of these is housed at the University of Edinburgh and will be used by the UK Quantum Chromodynamics (UKQCD) group of scientists from seven British universities.

UKQCD is a collaboration of particle physicists from the Universities of Edinburgh, Southampton, Swansea, Liverpool, Glasgow, Oxford and Cambridge and was formed in 1989 to simulate and study the behaviour of matter at the sub-atomic levels in the colourful field of quantum chromodynamics. It has since its founding, exploited a series of novel architecture computers for QCD simulations, becoming an internationally leading team. With the completion of the Edinburgh computer, the UKQCD scientists can probe the properties of quarks ever more closely.

Chris Sachrajda

Chris Sachrajda

Quarks are the fundamental particles that make up 99.9% of ordinary matter acting as the building blocks of hadrons, of which the best known are protons and neutrons. Quarks have proved impossible to separate, preferring to exist in colour-neutral groups of two or three. For quarks, colour is a property akin to electrical charge, rather than anything to do with the colours we see with our eyes. This indivisibility means that we know little about the basic properties of quarks. For instance, what are their precise masses? Why are there six different types? And, why are they so strongly bound together?

It is the strong nuclear force that binds quarks, a term that belies its weakness at the incredibly short distances between quarks themselves. But, try to separate any two (or three) quarks and this force begins to live up to its name. As such, much that particle physicists know about quarks is down to pure simulation.

Richard Kenway

Richard Kenway

The UKQCD computer is the first of three similar machines and has been operating since January 2005. The second computer was inaugurated in May 2005 at the RIKEN Brookhaven Research Center in Brookhaven National Laboratory in the USA. The third is part of the US Department of Energy Program in High Energy and Nuclear Physics, and is also installed at Brookhaven where it is currently undergoing testing.

UKQCD team member Chris Sachrajda of the University of Southampton explains the relevance of the machine. The QCDOC [QCD-on-a-chip] machine at Edinburgh, combined with new theoretical techniques which we have been developing, provides us with the opportunity to study the Strong Force to unprecedented precision, he says. This will enable us to extract detailed information about the fundamental constituents of nature, by combining our calculations with experimental data from the major accelerator laboratories. Southampton’s QCDgrid node will help the researchers there run simulations and exploit the emerging data.

The computers are built with processing chips specifically designed for the purpose, known as QCD-on-a-chip, or QCDOC for short. A little slower than the microprocessor in your laptop, the QCDOC chip was designed to consume a tenth of the electrical power, so that tens of thousands of them could be put into a single machine. The computers were designed and built jointly by the University of Edinburgh, Columbia University (USA), the RIKEN Brookhaven Research Center (USA) and IBM.

Each QCDOC machine operates at a speed of 10 Teraflops, or 10 trillion (i.e. million million) floating point operations per second. By comparison, a regular desktop computer operates at a few Gigaflops (a thousand million floating point operations per second), whilst IBM’s BlueGene, a close relative of QCDOC and the fastest computer in the world, operates at over 100 Teraflops.

We are certainly very excited by our new machine and the opportunities it affords, Edinburgh’s Chris Maynard told Spotlight. Richard Kenway, who led UK participation in the QCDOC Project, echoed the sentiment. After five years building this machine, it’s exhilarating to be able to compute in days things which take everybody else months, he says. Now we are about to run QCDOC for months to do the most realistic QCD simulation yet. It’s like standing on the shore of a new continent after a long voyage, we’ve chosen our path of exploration, but we don’t know what we’re going to find.

Further reading

http://phys.columbia.edu/~cqft/qcdoc/qcdoc.htm
Chris Sachrajda

http://www.phys.soton.ac.uk/staff/index.php?staff=cts
Richard Kenway

http://www.nesc.ac.uk/nesc/staff/rdkenway.html
RIKEN BNL Research Center

http://www.bnl.gov/riken/
Theorists get to grips with the strong force (PDF article)

http://www.physics.gla.ac.uk/lattice_EU_network/physics_world.pdf

Suggested searches

quarks
quantum chromodynamics
particle physics