About the Nobel Prize in Physics 1984
Carlo Rubbia Simon van der Meer
17 October 1984
The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 1984 jointly to Professor Carlo Rubbia, CERN, Geneva, Switzerland and Dr Simon Van der Meer, CERN, Geneva, Switzerland, for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction.
Carlo Rubbia and Simon Van der
Meer have been awarded this year's Nobel Prize in Physics for
"their decisive contributions to the large project, which led to
the discovery of the field particles W and Z, communicators of
weak interaction". Weak interaction is one of four fundamental
force fields in the universe. It operates deep inside matter
where quarks and leptones reside. Examples of weak processes are
radioactive 6-decays and also the nuclear processes in the sun
which control its power.
One expected on theoretical grounds that the weak interaction is
communicated by extremely heavy hypothetical particles, W and Z.
In 1976 Carlo Rubbia presented an idea to convert an existent
large accelerator into a storage ring for protons and
antiprotons. The W and Z particles could then be produced in
violent head-on collisions between the stored particles. Simon
Van der Meer had invented an ingenious method for dense packing
and storage of protons, now applied for antiprotons. Rubbia's
idea and Van der Meer's invention were combined in a large
project and the first collisions in the CERN superaccelerator
were observed in 1981. The discovery of the W and Z were
announced in 1983 by Rubbia and collaborating large teams of
scientists, basing the evidence on signals from detectors,
specially designed for this task.
The project at CERN, the European nuclear research organization
in Geneva, is the largest that has ever appeared in the context
of a Nobel Prize. Two persons in the project are outstanding -
Carlo Rubbia, who had and developed the idea, and Simon Van der
Meer, whose invention made it feasible.
Weak Interaction
The discovery of the heavy field particles W and Z culminates 50
years of scientific investigations of the nature of the weak
interaction. A milestone along the road of development was passed
by the discoveries of W and Z at CERN in 1983.
Weak interaction is one of four fundamental force fields in the
universe. It operates at the deepest level of matter, that of
quarks and leptons. Examples are radioactive ß-decays. The
power of the sum is also controlled by weak processes.
What roles are played by W and Z ?
The surplus energy in ß-decay radiates in the form of
electron and neutrino pairs. These pairs were assumed to be
created directly when neutrons were transformed into protons.
This was in 1934.
Now, 50 years later, we know that the pair creation is a two-step
process. In the first intermediate step the communicator
W- is emitted (in the example of neutron decay). In
other processes a W+ is emitted, in yet others a
Z0. In the final step - somewhat further away in time
and space - the W disappears and transfers energy etc. to the
electron neutrino pair. The distance in space and time is so
extremely short that the W has been hidden. The same holds for
Z0. In 1983 they were for the first time displayed in
the open.
Relation to electrical forces
The idea of introducing communicators in interactions is an old
one in physics. It is used in the modern treatment of electrical
forces. Two charged bodies interact at a distance by exchanging
photons, as if they were throwing balls to each other.
Beams of free photons from light, radio waves etc. The Nobel Prize in Physics in 1979 was
awarded to Sheldon Glashow, Abdus Salam and Steven Weinberg for
their mathematical theory of weak interaction. It not only solved
some difficulties with the direct process but was based on an
intimate unity between weak and electromagnetic interactions.
Besides the two heavy charged communicators W+ and
W- , the theory contains two neutral communicators -
one heavy, the other massless. The massless one is the photon.
The heavy Z0 represents something completely new. The
first time a process was observed, caused by the hidden
Z0, was in 1973 at CERN by an international team,
using the French-built Gargamelle bubble chamber.
The large project at CERN
One could not be certain that the communicators existed as long
as they remained hidden. To be convincing, they have to be
produced in free form. New research fields will then be opened
up. The existence of radio waves was discovered almost one
hundred years ago by Heinrich Hertz. The W and Z have been
produced and detected at CERN with evidence for their existence
as convincing as the one for radio waves by Hertz
The project started in 1976. At that time, energy was nowhere in
the world available in sufficient concentration for the creation
of the W or the Z.
Carlo Rubbia presented a new idea, proposed by him and two
American colleagues during an international conference in physics
in 1976. Rubbia brought the idea to CERN. Committing himself
intensely, exploiting his deep knowledge in broad areas and with
catching enthusiasm he succeeded in convincing the CERN
management that the project might well be feasible. The method
requires a copious supply of antiprotons (antimatter). Provided
this problem could be solved, W and Z could be created in frontal
collisions between antiprotons and protons in the new
superaccelerator, SPS, at CERN. The probability of a successful
collision could be estimated. In order to produce about ten
communicator particles, about a billion collisions have to occur.
To do that on a reasonable time scale the number of antiprotons
circulating in the SPS must be enormous, several hundred
billions.
Antiprotons do not exist in nature. They can be created in
batches in collisions at another of CERN's accelerators. However,
only a tiny fraction of one per cent of the required number of
antiprotons will be obtained in each batch. Almost insurmountable
difficulties are encountered when one tries to collect and
densely pack hundreds of thousands of batches of fresh
antiprotons.
Simon Van der Meer had some years earlier invented an ingenious
method for the dense packing or protons which are circulating in
an orbit in a vacuum chamber, guided by magnetic fields. The
method is rather sophisticated. Even experts found it hard to
believe in the possibility. The method was successfully tested at
CERN. It was finetuned for use on the current of antiprotons. Van
der Meer and his coworkers finally succeeded in increasing the
current of antiprotons several hundred thousands times using a
facility specially built for production, storage and dense
packing. The first collisions in SPS were made in the summer of
1981. The experiments started in November of the same year. The
hunt for expected and unexpected phenomena was on, and still
continues.
The few expected W's and Z's had to be found and measured in
detail. Measuring apparatus for this purpose was not readily
available. Carlo Rubbia gathered a group of scientists around
himself for the task of designing and constructing an enormously
large detector. It was adapted for the difficult task of catching
the communicators and measuring their properties. Another team of
scientists also took part in the successful hunt with their
detector specially built for this task.
Scientists and engineers in their hundreds have participated in
various phases of these large-scale projects for many years. They
come from laboratories in many countries, mainly member states of
CERN, and from CERN itself.
The CERN project is the largest which has appeared in connection
with a Nobel Prize. Two people are outstanding: Carlo Rubbia, who
had and developed the idea, and Simon Van der Meer, whose
invention made it feasible.
