Just prior to last week's dedication of the
B-Factory at the Stanford Linear Accelerator Center, 24 copies of the most complex digital
printed circuit board ever produced at Berkeley Lab were installed in BaBar, the
B-Factory's sole detector. These circuit boards, the product of a close collaboration
between physicists and engineers, will work together as a critical component of a trigger
system unlike the detector trigger system for any other high energy physics colliding beam
facility.
 Krista Marks of Berkeley
Lab, the chief engineer for this set of unique trigger circuit boards
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"When I first heard the specifications for this circuit board, I was skeptical it
could even be built!" says Krista Marks, the chief engineer for the 24 circuit
boards.
"We aimed the specifications extremely high and made it work because we had a
world class team," says Fred Kral, the chief physicist for the entire BaBar trigger
system.
The 24 circuit boards constitute the Track Segment Finder modules, the linchpin for the
Drift Chamber Trigger, one of the five subsystems that make up the BaBar trigger system.
Each of these boards bristles with 900,000 logic gates, a formidible array of hardware
which will enable the boards to sift through the 238 million beam crossings that will
occur every second in the B-Factory and select the estimated four events of significance
to the B-Factory's primary mission.
"Unlike trigger systems that essentially throw away a large percentage of the
physics events they produce, the BaBar trigger system will save all interesting
events," says Kral.
Adds Marks, "Also, unlike other trigger systems which merely signal that something
interesting happened, this electronics system processes data to also describe when the
event occurred."
The Drift Chamber Trigger, which was one of the many exclusive responsibilities
Berkeley Lab has for BaBar, is among the first components to be installed in the massive
detector.
"I don't know of any other high energy physics detector for which this powerful a
trigger was one of the first pieces in place," says Kral. "But we were able to
complete it within only one and a half years, thanks to our design methodology and the
quality of our team."
Marks says the team was the strongest she's ever worked with, and agrees that the
design methodology made possible the timely production of the Track Segment Finder, as
well as the other circuit boards that make up the complete Drift Chamber Trigger.
"The functional specifications were very mature after three years of simulation
studies of how the BaBar detector would respond to various physics and background
events," she says.
Rather than the usual physical testing through a series of prototypes, the trigger team
tested their board design using extensive simulation in state-of-the-art Computer Aided
Design (CAD) tools. The result was a prototype board with no layout or fabrication errors
that could serve as a production version.
"This methodology will be valuable for future projects in which we need to make an
errorless circuit board in a short amount of time," says Marks. "And it will be
essential for circuit boards with computer-like complexity."
The complete set of BaBar trigger electronics will feature a Drift Chamber Trigger, a
Calorimeter Trigger, and a Global Trigger. The first two receive and process data from the
Drift Chamber and the Calorimeter detectors, respectively, then send the results to the
third. The Global Trigger determines whether or not to transmit the event on to BaBar's
computers, which will perform subsequent background rejection.
Says Kral, "In terms of the response time for our electronics, collisions in the
B-Factory are essentially continuous. To meet this challenge, we designed a trigger that
is always live (in operation) and we therefore lose no data."
In addition, Kral says the trigger system's background rejection power will enable
physicists to use the B-Factory and BaBar to study other important phenomena besides CP
violation.
Other members of the BaBar trigger team included Antal Berenyi, Helen Chen, Khang Dao,
Scott Dow, Stefan Gehrig, Mandeep Gill, Carl Grace, Richard Jared, Jimmie Johnson, Armin
Karcher, Daniel Kasen, Frederick Kirsten, Christopher LeClerc, Michael Levi, Henrik von
der Lippe, Ted Liu, Andreas Meyer, Robert Minor, Alex Montgomery, and Alexandru Romosan.
