2. Why is an accelerator needed for investigating matter?
3. What modifications has the accelerator gone since its appearance in 1928?
4. What other problems besides technical should be taken into account in the construction of an accelerator?
• Reproduce the passage in English or in Russian.
CLASSWORK
READING (20B)
• Read the passages carefully and say why this discovery is of interest to physicists.
A) THE TROPHIES THAT WILL BE HUNTED WITH THE NEW ACCELERATORS
However much has been learned in the past 50 years, it would be misleading to suggest that the present understanding of elementary particles is even approaching finality or completion. The status ofthe field is tantalizing rather than satisfying1; there is no shortage of questions to be answered. A first order
... is tantalizing rather than satisfying — скорее заставляет испытывать танталовы муки, чем приносит удовлетворение of business for the new accelerators will be filling in the blanks in the catalogue of hadrons, particularly those that incorporate top and bottom quarks in their structure. It is also important to find out whether the list of quarks and leptons ends with the six of each that are now known or whether more will be found at higher energies. In a sense six quarks and six leptons are already too many; all ofthe ordinary matter in the universe could be constructed out ofjust four elementary particles: the electron, the electron neutrino and the up and down quarks. The existence of the other leptons and quarks, which appear only in high-energy-physics experiments, is a puzzle.
Another puzzle is the failure of all attempts so far to detect a free quark. Various theoretical constructs have been offered, after the fact, to explain why quarks should be permanently confined to hadrons. The possibility remains, however, that a quark can be knocked loose from a hadron if enough energy is supplied. Future experimental programs are therefore certain to include quark searches.
B) NEW STATE OF MATTER CREATED AT CERN
At a special seminar on 10 February, spokespersons from the experiments on CERN's Heavy Ion programme presented compelling evidence for the existence of a new state of matter in which quarks instead of being bound up into more complex particles such as protons and neutrons are liberated to roam freely.
Theory predicts that this state must have existed at about 10 microseconds after the Big Bang, before the formation of matter as we know it today, but until now it had not been confirmed experimentally. Our understanding of how the universe was created, which was previously unverified theory for any point in time before the formation of ordinary atomic nuclei, about three minutes after the Big Bang, has with these results now been experimentally tested back to a point only a few microseconds after the Big Bang.
Professor Luciano Maiani, CERN Director General, said: "Thecombined data com'mgfrom the seven experiments on CERN's Heavy Ion programme have given a clear picture of a new state of matter. This result verifies an important prediction of the present theory offundemental forces between quarks. It is also an important step forward in the understanding of the early evolution of the universe. We now have evidence of a new stale of matter where quarks and gluons are not confined. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and later to CERN's Large Hadron Collider. "
The aim of CERN's Heavy Ion programme was to collide lead ions so as to create immensely high energy densities which would break down the forces which confined quarks inside more complex particles. A very high energy beam of lead ions (33 TeV) was accelerated in CERN's Super Proton Synchrotron (SPS) and crashed into targets inside the seven different experimental detectors. The collisions created temperatures over 100 000 times as hot as the centre of the sun, and energy densities twenty times that of ordinary nuclear matter, densities which have never before been reached in laboratory experiments. The collected data from the experiments gives compelling evidence that a new state of matter has been created. This state of matter found in heavy ion collisions at the SPS features many of the characteristics ofthe theoretically predicted quark-gluon plasma, the primordial soup in which quarks and gluons existed before they clumped together as the universe cooled down.
The project is an excellent example of collaboration in physics research. Scientists from institutes in over twenty countries have participated in the experiments. The programme has also allowed a productive partnership to develop between high energy physicists and nuclear physicists. More importantly, this step forward has been made possible by the collaboration between the individual experiments. The picture of quark-gluon plasma resembles a jigsaw puzzle, with many pieces provided by the different experiments. The data from any one experiment is not enough to give the full picture but the combined results from all experiments agree and fit. Whereas all attempts to explain them using established particle interactions have failed, many of the observations are consistent with the predicted signatures of a quark-gluon plasma.
The results from CERN present strong incentive forthe future planned experiments. While all ofthe pieces ofthe puzzle seem to fit with a quark-gluon plasma explanation, it is essential to study this newly produced matter at higher and lower temperature in order to fully characterize its properties and definitively confirm the quark gluon plasma interpretation.
CERN Press Releases 2000
HOMEWORK
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