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Smashing success: accelerator gets cool upgrade.


A novel scheme for increasing the number of collisions in particle accelerators has boosted the performance of the world's highest-energy collider and promises to rev up others.

This scheme, called high-energy
1. Of or relating to elementary particles with energies exceeding hundreds of thousands of electron volts.
2. Yielding a large amount of energy upon undergoing chemical reaction.
3. Vigorous; dynamic.
 electron cooling, helped the Tevatron collider at Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab FERMILAB - Fermi National Accelerator Laboratory), physical science research center located near Batavia, Ill., est. 1968 as the National Accelerator Laboratory, renamed 1974 in honor of Enrico Fermi. It was built on the site of the former village of Weston. Universities Research Association operates it under contract to the U.S. Dept. of Energy. (Fermilab) in Batavia, Ill., last October to shatter the 23-year-old world record for particle-collision rates.

For decades, particle physicists have used electron cooling to control the properties of particles in low-energy accelerators, but they were daunted by the difficulty of high-energy cooling, comments beam-cooling specialist Fritz Caspers of the European Organization for Nuclear Research in Geneva. To finally develop and implement such a system is "a really great achievement," he says.

Accelerators must generate vast numbers of collisions to produce even a few of the exceedingly rare elementary particles
1. A knoblike body that appears on the luminal surfaces of mitochondrial cristae and is believed to be involved with the electron transport system.
2. Any of the subatomic particles that compose matter and energy, especially one hypothesized or regarded as an irreducible constituent of matter. Also called fundamental particle.
 sought by high-energy-physics researchers. In the Tevatron accelerator, discrete bunches of protons and antiprotons circulate in opposite directions around a 6-kilometer ring. They travel at nearly the speed of light. When these bunches cross paths at two locations in the ring, particles smash into each other and spawn sprays of other elementary particles elementary particles, the most basic physical constituents of the universe.

Basic Constituents of Matter



Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron. It turns out that protons and neutrons are made of varieties of a still smaller particle called the quark.
 that are recorded by huge detectors.

However, most protons and antiprotons zoom right past each other, explains physicist Sergei Nagaitsev, leader of electron cooling at Fermilab. That's largely because the antiproton bunches tend to be hot and therefore spread out. To pack antiprotons more tightly in each bunch, Nagaitsev and his colleagues created a separate electron accelerator that serves as the heart of the electron-cooling system. That accelerator ramps up electrons to the same velocity as that of the antiprotons and then injects the electrons into a ring. There, the two types of particles interact before the antiprotons enter the main ring and encounter the protons.

Because each electron weighs only a fraction of what an antiproton weighs, jostling among the particles tends to transfer energy to the electrons. Those energy transfers decrease random vibrations of the antiprotons, in effect cooling them, Nagaitsev explains. That, in turn, makes it possible to have more antiprotons in each bunch, increasing its density and the subsequent collision rate.

"The Fermilab work is particularly significant for us," says Ilan Ben-Zvi of Brookhaven National Laboratory Brookhaven National Laboratory, scientific research center, at Upton (town of Brookhaven), Long Island, N.Y. It was founded in 1947 by Associated Universities, a management corporation sponsored by nine eastern U.S. universities. The corporation ran the laboratory under a contract with the U.S. Dept. of Energy (DOE) until 1997, when safety problems led the DOE to replace it. Brookhaven conducts multidisciplinary scientific work, e.g. in Upton, N.Y. He and his team plan to build upon it to equip a giant accelerator there with even higher-energy electron cooling.

The Tevatron's surging collision rate increases the chances that the machine will yield important discoveries in coming years, Nagaitsev says. In the debris of future smashups, physicists will search for such long-hunted prizes as the Higgs boson boson: see elementary particles; Bose-Einstein statistics., thought to bestow mass on other particles, and supersymmetric particles, which are hypothetical sister particles to the particles already known (SN: 6/12/04, p. 371).

Many other tweaks to the Tevatron have contributed incrementally to its collision rate. However, electron cooling by itself has so far resulted in a roughly 50 percent increase in the Tevatron's instantaneous collision rate, Nagaitsev says. Another 50 percent boost might be possible with further improvements, he adds.

Nagaitsev and his colleagues describe their system in the Feb. 3 Physical Review Letters.
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Title Annotation:particle accelerators
Author:Weiss, P.
Publication:Science News
Geographic Code:1USA
Date:Feb 4, 2006
Words:513
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