D0 silicon microstrip tracker Page: 1 of 5
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FERMILAB-CONF-05-515-E
DO Silicon Microstrip Tracker
Sergey Burdin for DO CollaborationAbstract- The DO Run II silicon microstrip tracker (SMT) has
3 square meters of Si area. There are 792,576 channels read
out by 6192 SVXIIe chips on 912 read out modules. The SMT
provides track and vertex reconstruction capabilities over the full
pseudorapidity coverage of the DO detector. The full detector has
been running successfully since April 2002.
This presentation covers the experience in commissioning and
operating, the recent electronics upgrade which improved stability
of the SMT and estimates of the radiation damage.
Index Terms- Detector, Silicon, Tracker, Electronics, Radiation.
I. INTRODUCTION
T HE Silicon Microstrip Tracker (SMT) together with the
Central Fiber Tracker (CFT) provide tracking and ver-
texing at the DO Detector (Tevatron, Fermilab). The long
interaction region and large pseudorapidity acceptance (InI < 3)
led to a hybrid design of the SMT shown in Fig. 1, with
barrel detectors measuring primarily the r-O coordinate and
disk detectors which measure r-z as well as r->. Thus tracks
for high y particles are reconstructed by the disks, and tracks
of particles at small values of y are measured in the barrels.
The SMT information is heavily used for many DO analyses.
It is crucial for selection of the events with t- and b-quarks, as
well as for e/- separation.
Fig. 1. Isometric view of the DO silicon tracker
The SMT consists of six barrels which are 12 cm long
and have 72 ladders arranged in four layers. The two outer
barrels have single sided and double sided 2 stereo ladders.
The four inner barrels have double sided double metal (DSDM)
90 stereo and double sided (DS) 2 stereo ladders. The lad-
ders are mounted between two precision machined Beryllium
bulkheads.
Each barrel is capped with a disk of wedge detectors, called
the "F-disks". The F-disks are comprised of twelve wedges
made of double sided silicon wafers with trapezoidal shape. The
Presented at Nuclear Science Symposium & Medical Imaging Conference
S. Burdin (burdin@fnal.gov) is with Fermilab.stereo angle of the F-wedges is 30. To provide further coverage
at intermediate y, the central silicon system is completed with
a set of three F-disks on each side of the barrel. In the far
forward and backward region two large diameter "H-disks"
provide tracking at high n. The H-disks are made of 24 pairs of
single sided detectors glued back to back giving a stereo angle
of 15g.
II. SILICON MICROSTRIP TRACKER READOUT
The silicon detectors are read out using the SVXIIe chip,
which is fabricated in the UTMC radiation hard 1.2 pm CMOS
technology. Each chip consists of 128 channels, each including
a preamplifier, a 32 cell deep analog pipeline and an 8 bit ADC.
It features 53 MHz readout speed, sparsification, downloadable
ADC ramp, pedestal and bandwidth setting. The SVXIIe chips
and associated circuitry are mounted on a double-sided, 0.2
mm pitch, kapton flex circuit, the so called High Density
Interconnect, or HDI. The HDI is laminated onto a 300 pm
thick Beryllium substrate and glued to the silicon sensor. In case
of double-sided silicon ladders, the HDI is wrapped around one
silicon edge to serve both ladder surfaces. The total number of
HDIs in the SMT is 912.
Fig. 2 shows a sketch of the SMT readout setup. The HDIs
are connected through 2.5m long kapton flex cables, Adaptor
Cards (ACs) and 10m long pleated foil cables to Interface
Boards (IBs). The ACs are located on the face of the Central
Calorimeter. The IBs supply and monitor power to the SVXII
chips, distribute bias voltage to the sensors and refresh data and
control signals traveling between the HDIs and the Sequencers.
The Sequencers control the operation of the chips and convert
their data into optical signals carried over 1Gb/s optical links to
VME Readout Buffer boards. Data is read out from the chips,
transfered to the VRBs through the Sequencers whenever a
Level-1 accept is issued and held pending a Level-2 trigger
decision.
The SMT has been fully functional since April 2002. The
main operational goal is to keep high efficiency with low
detector downtime. This goal is compromised by unstable
HDIs: 46% of all HDIs were deactivated at least once due
to readout problems. In most cases these HDIs can eventually
be read out. The debugging process is complicated because
there is no access to the upstream electronics starting from the
Sequencers during Tevatron operation; only during shutdown
one can access the electronics and cables up to the Adaptor
Cards.
Before the Fall 2004 shutdown 160 HDIs were disabled and
80 of them were declared "dead" due to confirmed problems
in the unaccessible area. During the shutdown two approaches
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Burdin, Sergey. D0 silicon microstrip tracker, article, November 1, 2005; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc875056/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.