The beauty of matter

Text: Boris Hänßler

As yet, we do not know exactly what our universe is made of. The credit for part of what we do know goes to British researcher Brian Foster. Thanks to his work we understand more about the way protons are constructed and what forces are at work inside them. In Hamburg, the distinguished particle physicist is looking to usher in a new era in his discipline.

The world Brain Foster investigates is so tiny that we cannot even imagine it. He researches into quarks, the fundamental building blocks of our matter. Particle physicists have identified six quarks and their six antiparticles, aka antiquarks. Their structure and behaviour still pose any number of questions. It is completely unclear, for example, why quarks never occur singly, but always in pairs or groups – one of the major mysteries of modern physics.

As a Humboldt Professor for accelerator development and particle physics at the University of Hamburg Foster wants to discover the answer to this question, and others. “The next few years will see a new era in particle physics, and produce revolutionary results,” the British researcher believes. At the Hamburg research centre DESY he will analyse the data collected at the HERA accelerator up to 2007.

He will also work on the development of new technologies such as the International Linear Collider (ILC), a new 30 to 40 kilometre electron-positron accelerator being constructed at DESY in Hamburg – destined to be the largest in the world. It will help to open the door onto the elementary issues of matter, space and time. And quarks could be the key.

November Revolution in particle physics

It was only in the 20th century that physicists proved the existence of quarks. Atoms were thought to be the smallest units of matter until it was discovered that they were made up of electrons outside and protons and neutrons inside. In the 1960s, they were also robbed of their ‘elementary’ function when American physicist, Murray Gell-Mann, postulated even tinier particles, quarks, although he only came up with three at the time. He was awarded the Nobel Prize – not the last one to go to particle physicists. On 11 November 1974, researchers at Stanford University and the Massachusetts Institute of Technology announced the J/˜-Meson. This particle contained a fourth quark whose existence had been severely doubted until then. The Nobel Committee decided this discovery deserved a prize, too, and it has gone down in history as the ‘November Revolution’. “That was the day we first started to understand how particle physics really works,” says the Humboldt Professor.

And it was precisely on this day that the young graduate Foster arrived at the University of Oxford to be interviewed for a doctoral position. “The professors were so excited about the news that they could hardly bring themselves to talk to me,” he remembers. But Foster got the job and embarked on his career at a time when particle physics was about to change significantly. His experiments had a decisive influence on our understanding of the structure of protons and the forces at work in these particles.

Plumbing the ‘quark sea’

Nowadays we know that a proton is composed of two up quarks and a down quark. And then there are gluons which link the protons and neutrons in the nucleus of the atom. They are known as a ‘fundamental force’ – one of the four forces of the universe alongside gravitation, electromagnetism and radioactivity. Cavorting around in the protons next to the gluons are pairs of quarks-antiquarks. Physicists call it a ‘quark sea’. Interestingly, quarks always crop up in groups of three or as quark-antiquark pairs. If the link gets broken, a new one forms immediately – so far, no-one knows why. In the coming years in Hamburg, Foster hopes to solve this puzzle.

Brian Foster’s research brought him to the Hanseatic City at an early stage in his career as a member of the TASSO research group. In 1979, the group at DESY first proved the existence of gluons. “This was one of the central discoveries needed to put the standard model of particle physics on a sound scientific footing,” says Foster. He was certain that discoveries were dependent on the performance of the support apparatus: accelerators, detectors, analytic methods. So developing technologies became the second field in which the scientist made a name for himself. He designed a detection chamber for TASSO filled with gas, which made it easier to observe the particles because they reacted with the gas.

The first experiments with HERA, one of a new generation of accelerators, took place in Hamburg in 1992. At that time, HERA was the only storage ring in the world in which protons and electrons or their antiparticles could be made to collide. Foster’s team was able to measure the exact strength of the fundamental force: the closer together the quarks are, the less the force. And vice versa: the greater the distance, the stronger the force. To explain the reasons for this is one of the challenges to be met in future. But Brian Foster is convinced that with the new accelerator technologies he wants to develop at the University of Hamburg, he will be able to track down the causes.

And then? Will researchers discover even tinier particles? Or are quarks really made up of strings as string theorists suggest? Although Foster admits that this idea does have its charm, “I’m an agnostic. I produce data and analyse it.” Rather than adhering to one single theory, he believes that it is more important to keep an open mind.