Seven years after the idea was first proposed by
Berkeley Lab Deputy Director Pier Oddone, the B-Factory, a $177-million particle
accelerator facility unlike any other before it, was officially dedicated on Oct. 26 at
the Stanford Linear Accelerator Center (SLAC). The project is a collaboration between
SLAC, Berkeley Lab and the Lawrence Livermore National Laboratory.
Energy Secretary Bill Richardson, whose department funded the B-Factory's construction,
joined approximately 800 other persons who came from around the world to help celebrate
the dedication.
"The B-Factory will help examine one of nature's great secrets: why matter exists
in the Universe," said the Secretary. "I congratulate the three laboratories
involved for once again demonstrating why our national laboratories are the crown jewels
of this nation."
Other participants at the dedication ceremony included Congresswomen Anna Eshoo and Zoe
Lofgren, Martha Krebs, head of DOE's Office of Energy Research (soon to be the Office of
Science), Berkeley Lab Director Charles Shank, SLAC Director Burton Richter, Livermore
Director Bruce Tartar, DOE's Oakland Operations Manager James Turner, and Stanford
University Provost Condoleezza Rice.
"B-Factory" is the popular name given to the conversion of SLAC's PEP
collider (Positron-Electron Project) into PEP-II, an "asymmetric" collider in
which the two colliding beams of particles are not of equal energies. The collider's
mission is to produce copious quantities (with factory-like reliability) of B
mesons--sub-atomic particles containing a "bottom" quark, the fifth of the six
quarks believed to be fundamental constituents of matter.
Measuring the lifetime of a B meson and a B-bar meson--the B meson's antimatter
counterpart--offers scientists their best opportunity to study differences between matter
and antimatter, particularly the phenomenon known as CP violation
(charge-conjugation/parity). This phenomenon is widely believed to be responsible for the
fact that during the first split seconds of the Big Bang, the process of creation favored
matter over antimatter.
Oddone first proposed the use of an asymmetric collider to produce B particles while he
was the director of the Lab's Physics Division. His idea was to create a separation in
space between the decay products of individual B particles. A collision between an
electron and a positron--the electron's antimatter counterpart--yields a particle known as
the upsilon 4S, which immediately decays into a B meson and a B-bar meson. These B
particles in turn decay into a host of other charged and neutral particles whose detection
can provide a wealth of information.
In a collider where the energies of the two beams are equal, the newly created B
particles would remain nearly stationary, making it all but impossible to study the time
evolution of their decay products. Under Oddone's asymmetric scheme, when the two beams
collide, the B particles are carried downstream in the direction of the higher energy
beam. This forward motion with respect to a laboratory frame of reference enables the
decay products to separate, allowing scientists to observe the distance between their
points of decay.
For the B-Factory, the asymmetric rings are the High Energy Ring (HER), which will
store electrons at an energy of 9 GeV (billion electron volts), and the Low Energy Ring
(LER), which will store positrons at 3.1 GeV. The rings, both of which measure nearly 2.2
kilometers in circumference (1.36 miles), are stacked together in the same tunnel with the
LER positioned immediately above the HER.
The HER is an upgrade of the old PEP ring. The LER is something brand new, among the
most challenging storage rings ever designed. Berkeley Lab had primary responsibility for
the LER's design, construction, and commissioning, which was achieved under the leadership
of Michael Zisman, a physicist in the Accelerator and Fusion Research Division.
Because the decay of a B particle is such a rare event, tens of millions of B/B-bar
pairs must be produced in order for scientists to record any significant data. This
requires unprecedented "luminosity"--a measurement of the rate of particle
collisions. The B-Factory's design calls for a luminosity of 3 x 1033 (3 followed by 33
zeros) collisions per square centimeter per second, which is at least 10 times better than
the highest luminosity achieved with the best machines in the world today.
Collisions of such luminous magnitude generate a tremendous volume of data. Sifting
through this data for interesting physics will be a challenge for BaBar, the B-Factory's
sole detector. Construction of the $80 million, 1,000 ton BaBar detector is another huge
collaboration, involving researchers from ten countries. Berkeley Lab researchers are
playing a key role in the design and construction of BaBar as well.
