Nobel laureates will be among the distinguished guests at a symposium at CERN1 on 16 September. The symposium will celebrate the double anniversary of major discoveries at CERN that underlie the modern theory of particles and forces. It will also look forward to future challenges and opportunities as the laboratory moves into a new arena for discovery with the construction of the Large Hadron Collider. The symposium will end with a panel discussion(*) on the future of particle physics, chaired by Carlo Rubbia.
Twenty years ago, in 1983, CERN announced the discovery of particles known as W and Z, a discovery that brought the laboratory its first Nobel Prize in 1984. Ten years previously, physicists at CERN had already found indirect evidence for the existence of the Z particle in the so-called “neutral currents”. The charged W and neutral Z particles carry one of Nature's fundamental forces, the weak force, which causes one form of radioactivity and enables stars to shine. These discoveries provided convincing evidence for the so-called electroweak theory, which unifies the weak force with the electromagnetic force, and which is a cornerstone of the modern Standard Model of particles and forces.
This brought modern physics closer to one of its main goals: to understand Nature's particles and forces in a single theoretical framework. James Clerk Maxwell took the first steps along this path in the 1860s, when he realised that electricity and magnetism were manifestations of the same phenomenon. It would be another hundred years before theorists succeeded in taking the next step, unifying Maxwell's electromagnetism with the weak force in a new electroweak theory.
An important step towards confirming electroweak unification came in 1973, when the late André Lagarrigue and colleagues working with the Gargamelle bubble chamber at CERN observed neutral currents - the neutral manifestation of the weak force that had been predicted by electroweak theory but never previously observed. Later that decade, Carlo Rubbia of CERN proposed turning the laboratory's most powerful particle accelerator into a particle collider, an idea that received the support of the then Directors General, John Adams and Léon Van Hove. By colliding counter-rotating proton and antiproton beams head on, enough energy would be concentrated to produce W and Z particles. This was made possible, in particular, through Simon van der Meer's invention of "stochastic cooling" to produce sufficiently dense antiproton beams. By 1981 the search for the W and Z particles was on. The observation of W particles by the UA1 and UA2 experiments was announced at CERN on 20 and 21 January 1983. The first observation of Z particles by UA1 followed soon after, with the announcement on 27 May.
In 1979, three of the theorists responsible for the electroweak theory, Sheldon Glashow, Abdus Salam and Steven Weinberg, were awarded the Nobel Prize. In 1984, Carlo Rubbia and Simon van der Meer shared the Prize for their part in the discovery of the W and Z particles. The discovery also owes much to the development of detector techniques, in particular by Georges Charpak at CERN, who was rewarded with the Nobel Prize in 1992. The results ushered in more than a decade of precision measurements at the Large Electron Positron collider, which tested the predictions of the Standard Model that could be calculated due to the work of theorists Gerard 't Hooft and Martinus Veltman, who shared the Nobel Prize in 1999.
In addition to reflecting on past findings, speakers at the September symposium will also talk about the future of CERN, including the Large Hadron Collider, set to switch on in 2007. By colliding particles at extremely high energies, the LHC should shed light on such questions as: Why do particles have mass? What is the nature of the dark matter in the Universe? Why did matter triumph over antimatter in the first moments of the universe, making our existence possible? What was the state of matter a few microsceconds after the Big Bang?
(*) The members of the a panel will be : CERN's Director General Luciano Maiani, together with Robert Aymar (Director General of CERN from 1 January 2004), Georges Charpak, Pierre Darriulat, Simon van der Meer, Lev Okun, Donald Perkins, Carlo Rubbia, Martinus Veltman, and Steven Weinberg.
The symposium will be open to the public, and will run from 9 a.m. to approximately 6 p.m.
The full programme and further information, photos, on the symposium are available here!