Experimenting with 40 Trillion Electron-Volts: It Takes Hundred of Physicists Several Years to Design Experimental Detectors for the Superconducting Super Collider

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Experimenting With 40 Trillion Electron-Volts

With much of the emphasis recently on the competition among 25 states to be the site of the proposed Superconducting Super Collider (SN: 9/12/87, p. 167), the ambitious physics of the project tends to get lost. But to anyone involved in particle physics, the SSC involves a fantastic amount of energy, and physicists' eyes tend to gleam as they talk about what they will do with it--or rather, what nature will do with it while they watch. Each head-on collision of two protons in the SSC would provide 40 trillion electron-volts (40 GeV) of energy. That's 40,000 times the mass of a proton.

For several years now, particle physicists have gathered for a couple of weeks each summer to work out their ideas on how to design the equipment that will record the results of those collisions, and gradually the designs are beginning to jell. This year's Workshop on Experiments, Detectors and Experimental Areas for the Super Collider, held at the University of California at Berkeley, produced drawings of large pieces of experimental equipment that seem to be settling into basic categories.

The installations the experimenters discuss are large and complicated. As Roger Cashmore of the Fermi National Accelerator Laboratory in Batavia, Ill., points out, it takes about five years to build one of these detectors. If construction of the SSC goes forward on schedule, completion is expected in 1996. Therefore, in a couple of years physicists will have to develop these concepts into plans out of which hardware can be made.

They are not there yet, but scientists are standing at blackboards drawing up arrangements of different elements they think they need. As they do, they get sardonic comments from the audience:

"Amazing,' says one observer, "how they plan to levitate a heavy magnet like that!'

"They intend it to be superconducting,' says another, pushing in the needle a little farther.

Yes, they intend it to be superconducting, but no, they do not intend to levitate many tons of magnet by the Meissner effect. (A piece of metal in a superconducting state will expel a magnetic field from within itself. As has been demonstrated recently in television news reports of the new high-temperature super-conductors, the repulsion so generated will levitate a small object.) As Cashmore points out, "These things don't just float in midair.' There is a lot of engineering design to be done, and that could require tradeoffs with characteristics important to the data-taking. Particularly, the supports for heavy items like magnets could invade and degrade the hermeticity, the self-contained and sealed-off character, that experimental physicists desire in elements of the detecting equipment.

The physicists want the detectors to be able to identify the stable and the fairly long-lived radioactive particles that come out of the proton-proton collisions and determine the energies they carry and the size and direction of their momenta. Most of the unknown particles they seek will be too short-lived to make much direct impression on the detectors, so the presence of any of them will be revealed by the identity and behavior of its decay products. The name of the game is by their fruits shall ye know them.

The list of things they want to look for is fairly long. All these things are apparently heavier than particles now known and so require more energy for their production. Some of the things on the list would contribute to a rounding out and deeper understanding of the present "standard model,' which contains successful theories of two important parts of particle physics. Others pertain to attempts to go beyond the standard model to unite its elements with explanations of phenomena not now included and produce a more comprehensive theory. Finally, some theoretical exercises seek to go below the standard model to see whether there is a level of reality and structure below the most basic one now contemplated by the standard model. …