A major milestone was achieved last month when the ATLAS silicon pixel
detector was installed at CERN in Geneva, Switzerland for the ATLAS
experiment at the Large Hadron Collider(LHC). The ATLAS silicon pixel
detector has 80 million channels and is the most complex detector of its
type every constructed. The ATLAS group at LBNL from the Physics and
Engineering Divisions started work on this detector about 15 years ago
and has led the pixel project from conception through the recent
installation.

The endcap regions of the pixel detector, major elements of the overall
support structure and all of the internal electrical and cooling
services were designed and sub-elements fabricated at LBNL. One-by-one
these parts of the pixel detector were shipped or carried to CERN (see
<http://www.lbl.gov/Publications/Currents/Archive/May-19-2006.html#head1>
for how the endcaps were flown to CERN). All major parts were delivered
to CERN by the end of 2006.

A large team of senior physicists, postdoctoral fellows, engineers,
graduate students and technicians was formed at CERN, including frequent
commuters from Berkeley, to complete the assembly of the pixel detector
in collaboration with other teams from the Czech Republic, France,
Germany, Italy, elsewhere in the US and CERN. The delicate process of
assembling and testing the pieces of the pixel detector took place in a
large clean area in a building near the access shafts to the ATLAS
detector, which is located deep underground.

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height="2.4277777777777776in"}

Some members of the LBNL pixel team (and pixel team member from Italy
and the Czech Republic) after completion of the assembly of the ATLAS
pixel detector at CERN. The pixel detector is shown in the background on
its assembly fixture.

The assembled pixel detector was transferred in June from its assembly
fixture to a transport fixture for the journey to the underground ATLAS
detector. During a short break in the rainy weather in Geneva, the pixel
detector inside the transport fixture was rolled out of the clean room,
picked up by a portable crane and lifted into an adjacent building over
the large vertical access shafts to the ATLAS detector.

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height="4.008333333333334in"}

The ATLAS pixel detector inside its transport fixture being lowered
through the large vertical access shaft to the ATLAS detector deep
underground.

The pixel detector and fixture were then placed on large, adjustable
tables to position the detector for final insertion into the ATLAS
detector. \*\*\*\*You might want to skip this figure \*\*\*\*\*

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height="3.3027777777777776in"}

The ATLAS pixel detector inside its transport fixture being positioned
for final insertion into the ATLAS detector.

The final home of the pixel detector in the ATLAS detector is a 6.5m
long carbon-composite support tube with rails to guide the insertion of
the pixel detector. This tube (in three sections) and the precision
structures for mounting and guiding the pixel detector into place were
made at LBNL and installed before the pixel detector was lowered into
position.

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height="4.008333333333334in"}

The LBNL crew pulling in the pixel detector while monitoring electrical
signals and watching miniature webcams (on laptops). On the right is Tom
Johnson, mechanical technician from the Engineering Division, in the
middle is Neal Hartman, mechanical engineer also from the Engineering
Division and, on the left, Michael Leyton, a physics graduate student
from UC Berkeley.

The pixel detector was very slowly moved from its transport fixture into
the support tube. It took about two days to complete this process since
the clearance between the pixel detector and the supporting tube is less
than one millimeter in a number of locations.

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height="4.008333333333334in"}

Dr. Kevin Einsweiler(on the right, from the Physics Division), the
overall ATLAS Pixel Project Leader and LBNL Group Leader at CERN and
Eric Anderssen (on the left, from the Engineering Division), lead LBNL
mechanical engineer, watching the pixel detector as it is installed into
the ATLAS detector.

After a few heart stopping moments, a bit of fine adjustment and some
last minute filing of a few corners, the pixel detector move gently into
its final resting place on June 28.

In one sense, this culminates many years of the invention and
development of the silicon pixel technology that began at LBNL near the
end of the1980s. On the other hand, a new chapter is about to begin. The
electrical and cooling connections that are needed to operate the pixel
detector will be carefully made over the remainder of 2007. And then
operation of the detector will begin, first using cosmic rays, and
finally the Large Hadron Collider will turn on in the summer of 2008.