New fundamental particle discovered: the anti-xi-minus
The discovery of the xi-minus antiparticle, a positively charged xi and one of the few hitherto undiscovered "strange particles", was reported simultaneously in the Physical Review Letters of 15 March by physicists working at CERN and at the Brookhaven National Laboratory.
Thus one of the two remaining question marks on the list of so-called "elementary" particles can now be replaced by factual evidence. As professor Weisskopf [then director-general of CERN] has commented: "This is an important discovery. In filling a gap in the theoretical knowledge of fundamental physics, it allows physicists the world over to base more firmly their investigations on one of the great riddles of our time: what is matter made of and why is it so?"
The elementary particles now number 30. At the end of the list the heaviest are the xi particles, which are also called cascade particles. They have either a negative or zero electric charge and a mass of about 2580 times that of the electron, one of the fundamental blocks of nature, which is taken as the unit of particle mass. The xis are thus listed by physicists as heavy particles, or baryons, in one of four classes of particles. They decay in 10-10 s (one tenth of a thousandth of a millionth of a second), each into a lambda particle and a pion. It is the antiparticle of the negative xi (a positively charged xi) that has now been discovered.
In the CERN experiment that led to the discovery, 85,000 pictures were taken just before last Christmas in the 81 cm hydrogen bubble chamber. This apparatus was built by a group of engineers from the Department "Saturne" of the Centre d'Études Nucléaires de Saclay, France, and physicists from the Laboratoire de Physique, École Polytechnique, Paris. It was installed at CERN near the largest European accelerator, the 28,000 million electronvolt proton synchrotron. The accelerated protons hitting a target produced secondary particles, from which antiprotons with an energy slightly above 3 GeV were selected and transported in a 100 m long channel to the bubble chamber, by means of an electrostatic separator, magnetic lenses and magnets.
About 15 European physicists can be considered as responsible for the discovery made at CERN. They decided to credit not their own personal contribution but the co-operative effort of the CERN European enterprise, coupled with the work of the Paris École Polytechnique and Department Saturne of Saclay.
• Taken from CERN Courier March 1962 p4.
US government approves Project M
For the record, we would like to report that "Project M" (for Monster!) has received US government approval, and the first moves are being made in the construction of what will be the largest and most expensive research instrument of its kind in the world.
This is the 20 GeV electron linear accelerator, to be built at Stanford University, California, financed by the US Atomic Energy Commission. It will accelerate electrons inside a straight vacuum tube 2 miles (3 km) long, in a concrete tunnel buried under 11 m of earth. Every 12 m, radio waves will be fed into the tube from a total of 240 large klystron oscillators to provide the energy to speed up the electrons to 99.999999% the speed of light. Proposed experiments include studies of the processes induced by high-energy electrons, studies of nuclear-particle structure, experiments with secondary particle beams produced by the high-intensity electron beam, a test of the basic theory of electromagnetism, maybe even the study of new particles and other phenomena as yet unknown. It is planned eventually to raise the maximum energy to 40-45 GeV by feeding power from 1 klystron every 3 m.
•Taken from CERN Courier March 1962 p9.
Editor's note
In 1962 CERN Courier reported on the discovery of the anti-xi-minus, while just over 40 years later experiments are beginning to discover what seem to be exotic relatives of the xi, the so-called pentaquarks. The discovery of new particles is a continuing theme in particle physics, with the discovery of the W and Z particles being one of CERN's major achievements.