to Overhaul Muon Detector
By Davide Castelvecchi
is getting ready for the most extensive overhaul in its
five years of operation. During the accelerator’s and detector’s yearly
down time, starting August 1 this year and again next summer, crews will
completely replace the barrel part of the muon system, one of BABAR’s
five main particle detectors. A team led by Charlie Young (EA) manages
the SLAC portion of the project, which is a US-Italian collaboration
involving scientists from several universities and from Italy’s INFN. It
is globally managed by Roberto Calabrese of Università di Ferrara and
Stew Smith of Princeton University.
Angelo Cotta Ramusino of INFN
Ferrara works on the the electronics for testing LST tubes.
(Photo by Davide Castelvecchi)
The current system, made of resistive
plate chambers, catches an estimated 50 percent of the muons that cross
it. The new one will bring that close to 100 percent. “With the new
system,” Young says, “we can exploit the full potential of the
The new muon system will employ a technology called limited streamer
tubes (LSTs), developed by Italian physicists and used successfully in
the SLD as well as at a number of other labs. The 12-foot-long,
one-inch-thick plastic tubes are filled with gas that is ionized by the
passage of highly energetic particles. High-voltage wires running inside
the tubes magnify and pick up the resulting ionization signals.
LSTs will replace the current muon detectors in 12 of the 18 concentric
gaps in the iron barrel, BABAR’s
massive, hexagonal outer structure. Six layers of brass will fill the
remaining gaps. The LSTs will mainly pick up muons, the only particles
that can easily zip through the iron layers. The additional layers of
brass will improve efficiency by blocking other types of particles.
An Italian company that specializes in the production of particle
detectors is manufacturing the core of the LSTs under the watchful eye
of Italian and U.S. physicists, and shipping them to Ohio State and
Meanwhile, a SLAC team has set up working space at End Station A (ESA)
to manufacture thin copper planes and strips. Glued on each layer of
LSTs, the strips will help locate the ionization signals, while the
planes will provide grounding.
The strips will also go to Princeton and Ohio State, where physicists
will assemble and test the LST modules, and ship them to SLAC for
In all, 700 finished modules will get here, including 100 for spares.
Mark Convery (EB) and his colleagues will arrange all modules in racks
in the CEH for three phases of quality control. “Our plan is to test all
of them in parallel,” Convery says. Just by sitting there, the modules
will prove themselves by detecting cosmic rays, the free high-energy
particles supplied courtesy of the Universe.
A group of engineers, led by Angelo Cotta Ramusino of Ferrara are
working on read-out electronics at the CEH.
During the ten weeks of down time this summer, crews will get a month
and a half of access to the gaps in the iron barrel. They will install
modules during the day and evening and test them at night. “We’ll be
doing at least two shifts a day, maybe three toward the end,” Convery
says. 200 modules will go in this year, and the remaining 400 in 2005.