a
measure for the number of collisions achieved. Two collider experiments, CDF and
DZero, will present new results based on these datasets in the upcoming months.
"High luminosity is the name of the game for particle
accelerators," said DZero co-spokesperson Terry Wyatt, University of Manchester.
"We are in a great position to make some exciting discoveries with the data we
have.
With the prospect of doubling the dataset in 2006 and
again in 2007, and with 8,000 inverse picobarns expected by the end of Collider
Run II, there is huge future potential."
Following extensive upgrades, the high-energy Tevatron
collider racked up a series of records in 2005 (see footnote), doubling the
average peak luminosity
and raising the world record
for peak luminosity at a hadron collider to 17x10^31 inverse centimeter square
per second. A scheduled shutdown, from the end of February to the middle of
June, 2006, is expected to boost the Tevatron performance even further.
Particle physics at colliders is strikingly similar to
shooting pool (a.k.a. pocket billiards): the greater the number of collisions
created, the greater the likelihood of success. But while one billiard ball
classically colliding with another billiard ball always adds up to two billiard
balls, the near-light-speed quantum environment of E=mc2 changes the picture
completely for particle collisions.
"Imagine a car crash," said Steve Holmes, Associate
Director for Accelerators at Fermilab. "Two 2,500-pound Minis run into each
other and, instead of a fender rattling to the pavement, a 6,500-pound Hummer
pops out. The more collisions we produce, the better the chance we have of
finding something rare."
The Tevatron uses superconducting magnets to steer protons
and antiprotons around a 4-mile ring, creating collisions at the world record
energy of close to 2 trillion electron volts (TeV). The challenge in creating
the largest possible number of collisions is to produce as many antiprotons as
possible and to squeeze them across the smallest achievable area over the
longest possible span of time.
Tevatron luminosity depends on having roughly equal
numbers of protons and antiprotons in the colliding beams. Producing protons is
easy, by particle physics standards: remove the electrons from hydrogen
molecules, and you have single protons. Producing antiprotons is not easy, by
any standard:
colliding beams of protons with a fixed target made of
nickel, with every million collisions producing about 18 antiprotons.
Ultimately, Tevatron luminosity depends on the number of antiprotons available
for collisions.
"In the past 14 months, the peak production rate for
antiprotons has increased substantially, from 150 billion antiprotons per hour
to 200 billion," said Roger Dixon, head of the Fermilab Accelerator Division.
"We fully integrated the Recycler antiproton storage ring into our accelerator
operations, and we greatly increased the antiproton beam density by implementing
electron cooling."
Fermilab spent four years and $260 million to upgrade its
accelerators and detectors, from 1996 to 2000. When the lab started Tevatron
Collider Run II in March 2001, the progress on luminosity was sluggish. To
improve the performance, accelerator experts focused on increasing the
antiproton production rate; providing a third stage of antiproton cooling
(concentrating the beam using the new Recycler storage ring); and increasing the
transfer efficiency of antiprotons to the Tevatron. The result of these steps:
more collisions than ever before, and the best prospects for scientific
discoveries.
There is no time like the present for Fermilab to make big
news with its luminosity improvements. The Large Hadron Collider (LHC) at the
European laboratory
CERN will be turning on in 2007, with collisions at an
energy seven times higher than the Tevatron can produce. Boosting the Tevatron
luminosity enhances Fermilab’s chances for discoveries before the LHC creates a
significant number of collisions.
"We know that the LHC will assume the high-energy frontier
once it is operational, but we also know that discoveries are the best way to
position ourselves at the forefront of the field and help us to secure future
projects," says Fermilab Director Pier Oddone. "The Fermilab luminosity upgrades
will take us there."
Details on the luminosity upgrades as well as information
on the scientific goals of Collider Run II are available online
here>>.
Fermilab is a national laboratory funded by the Office of
Science of the U.S. Department of Energy, operated by Universities Research
Association, Inc.
Footnote: Between December 2004 and February 2006, the
average peak luminosity of the Tevatron collider doubled from 7x10^31
cm^(-2)sec^(-1) to 14x10^31 cm^(-2)sec^(-1). Two charts illustrating the series
of luminosity records set during this time period can be found
here>>.
