Carlo Rubbia - Experimental Physics Career

Experimental Physics Career

In 1976, he suggested adapting CERN's Super Proton Synchrotron (SPS) to collide protons and antiprotons in the same ring and the world's first antiproton factory was built. The collider started running in 1981 and, in early 1983, an international team of more than 100 physicists headed by Rubbia and known as the UA1 Collaboration, detected the intermediate vector bosons, the W and Z bosons, which had become a cornerstone of modern theories of elementary particle physics long before this direct observation. They are believed to carry the weak force that causes radioactive decay in the atomic nucleus and controls the combustion of the Sun, just as photons, massless particles of light, carry the electromagnetic force which causes most physical and biochemical reactions. It is also believed that the weak force has played a fundamental role in the nucleosynthesis of the elements, as studied in cosmology and the big bang. These particles have a mass almost 100 times greater than the proton. In 1984 Carlo Rubbia and Simon van der Meer were awarded the Nobel Prize "for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction"

To achieve energies high enough to create these particles, Rubbia, together with David Cline and Peter McIntyre, proposed a radically new particle accelerator design. They proposed to use a beam of protons and a beam of antiprotons, their antimatter twins, counter rotating in the vacuum pipe of the accelerator and colliding head-on. As a result, scientists had to develop a number of techniques for creating and handling intense beams of antiprotons.

In addition to the observation of the intermediate vector mesons, the CERN proton-antiproton collider dominated the scene of high energy physics from its first operation in 1981 until its close in 2002, when the Tevatron at Fermilab took over this role. An entirely new phenomenology of high energy collisions has resulted, in which strong interaction phenomena are dominated by the exchange of the quanta of the strong force, the gluons, particles which are similar to the intermediate vector bosons, although, like the photons, they are apparently massless. Instead, the W and Z particles are among the heaviest particles so far produced in a particle accelerator.

Together, these discoveries provide strong evidence that theoretical physicists are on the right track in their efforts to describe Nature at its most basic level through the so-called "Standard Model". The data on the intermediate vector bosons confirm the predictions included in the "electroweak" theory, which gained the 1979 Nobel Prize for Physics to Steven Weinberg, Sheldon Glashow and Abdus Salam. The "electroweak" theory attempts to unite two of the four forces of nature—the weak and the electromagnetic forces—under the same set of equations. It provides the basis for work on the long-standing dream of the theoretical physicists, a "unified field theory", encompassing also the strong force which binds together the atomic nucleus, and ultimately, gravity.

In 1970 Rubbia was appointed Higgins Professor of Physics at Harvard University, where he spent one semester per year for 18 years, while continuing his research activities at CERN. In 1989, he was appointed Director-General of the CERN Laboratory.

Rubbia has also been one of the leaders in a collaboration effort deep in the Gran Sasso Laboratory, designed to detect any sign of decay of the proton. The experiment seeks evidence that would disprove the conventional belief that matter is stable. The most widely accepted version of the unified field theories predicts that protons do not last forever, but gradually decay into energy after an average lifetime of at least 1032 years. The same experiment, known as ICARUS and based on a new technique of electronic detection of ionizing events in ultra-pure liquid argon, is aiming at the direct detection of the neutrinos emitted from the Sun, a first rudimentary neutrino telescope to explore neutrino signals of cosmic nature.

Carlo Rubbia further proposed the concept of an energy amplifier, a novel and safe way of producing nuclear energy exploiting present-day accelerator technologies, which is actively being studied worldwide in order to incinerate high activity waste from nuclear reactors, and produce energy from natural thorium and depleted uranium. The energy resources potentially deriving from these fuels will be practically unlimited and comparable to those from fusion.