\section{CHARGED PARTICLE TRACKING DETECTORS}
\label{sec-trackers}

\subsection{Outer Trackers}

The outer tracker is the charged particle tracker at largest radius
within the calorimeter.  Outer trackers perform two functions.  The
first is measuring the momentum and charge of particles
produced in the collision, and the second is to provide
pattern recognition assistance for the silicon detectors.

A particle with non-zero charge $q$ and momentum $p$ in a 
solenoidal magnetic field along the $z$-direction
of strength $B$ will travel in a helix with radius $r$
given by

\[ r = \frac{p_T}{qB} \]

where $p_T = \sqrt{p_x^2 + p_y^2}$.  So, by measuring
the track's curvature in the $r-\phi$ plane, we
effectively measure $p_T$.  By measuring the
track's direction in the $r-z$ plane, we measure
$p_T/p_z$, which completes our measurement of the
3D momentum vector of the particle.

Tracks in these detectors typically have several
dozen hits, which allows for highly efficient
and pure identification of these tracks.  Silicon
trackers in these detectors have of order a 
half-dozen hits, and while they can be used
standalone, a much better way to use them is to
find the track in the outer tracker and project
this track back into the silicon.  Once the
approximate trajectory in the silicon detector
has been established, the tracking algorithm
can search the silicon detector for hits and
use these hits to improve the track measurement.
This technique uses each component to it's best
advantage: the silicon tracker measures the
tracks point of origin and initial direction,
and the outer tracker measures the track's
momentum.

\subsubsection{THE D\O \ SOLENOID  AND SCINTILLATING FIBER TRACKER}

Perhaps the most substantial improvement to the D\O \ detector for Run~II was 
the addition of a superconducting solenoidal magnet.  D\O \ has a tracking 
bore a factor of two smaller than CDF, and since the momentum resolution
of a solenoidal tracker of radius $l$ goes as $1/Bl^2$, it is 
highly desirable from a pure tracking perspective for D\O \
to maximize their field strength.  While 3~Tesla and even 4~Tesla magnets have 
been constructed, D\O \ chose to use a 2~Tesla magnet.  Higher field 
magnets need to be thicker to support both the additional coils and to 
withstand the extra $B^2$ stresses, and this has two undesirable 
effects: the cost rises as $B^{1.324}$ \cite{MagnetCost} and
that more inert material is placed in front of the electromagnetic 
calorimeter.  A field strength of 2~Tesla optimizes the overall detector
performance.

Having a magnetic field will enhance the
D\O \ detector in many ways:

$\bullet$  It gains the ability to measure the 
momentum and charge of electrons and hadrons.

$\bullet$  Muon momentum measurement is improved
because the muon momentum can be measured
in the central
magnetic field, before the muon has scattered
in the steel of the muon toroids.  Additionally,
this allows for the comparison of the muon's
momentum as measured in the solenoid to the
momentum as measured in the toroids.  For muons
from pion and kaon decays, these quantities are
less likely to match than for muons from gauge
boson or heavy flavor decays.  Thus D\O \ has
an additional handle on the identification of
these muons.

$\bullet$ The ability to measure momentum of charged particles in 
Levels~1-3 of the trigger.  

$\bullet$ The ability to reject photon 
conversions to $e^+e^-$ pairs.  In the Run~I
configuration, a photon could convert to
an electron-positron pair, and both particles
would continue on to the calorimeter on the 
same path.  The signature of these events
would be a single track pointing at an
electromagnetic cluster, and such a photon
could therefore be misidentified as an electron.
(Some of these could be rejected by measuring 
the ionization due the ``electron" - if it
was obviously too high to be from a single 
particle, the object could be identified as a
photon conversion.  Unfortunately, this 
technique is not 100\% efficient.)

$\bullet$  The ability to calibrate their detector
in situ.  The tracking scale can be determined
by fitting the mass of known resonances, such
as the $J/\psi$ and the $Z$ boson.  This can then be transfered
to the electromagnetic calorimeter by examining
a sample of electrons and insuring that the
energy as measured by the calorimeter matches
the momentum as measured by the tracker.  Then
this can be transfered to the hadronic calorimeter 
by requiring transverse momentum be balanced in
events with a photon balancing a jet.

Mechanically, the D\O \ outer tracker is a 
simple device.  Layers of scintillating fiber
are placed on carbon-fiber composite cylinders.
When a particle travels through one of these 
fibers, the scintillator emits light, which is
totally internally reflected down the fiber,
coupled to a clear fiber, and transported
to a solid-state light detector.  Fig.~\ref{fig-d0-tracker}
shows a side view of the tracker.

\begin{figure}
\begin{center}
\epsfxsize=4.5 in
\epsfbox{d0-tracker.eps}
\end{center}
\caption{D\O 's scintillating fiber tracker.}
\label{fig-d0-tracker}
\end{figure}

In detail, the D\O \ central fiber tracker~\cite{wayne} consists of 
scintillating fibers mounted on eight concentric cylinders made from 
a composite of layers of high modulus of elasticity carbon fiber 
sandwiching structural foam. The cylinders range in radius from 20 to 50 cm 
and  are about 2.5 m in length, except for the inner two,
which are about 1.7 m in length. The scintillating fibers are 
double clad, 835 microns in diameter, and 
are constructed in ribbons each 128 fibers wide composed of
a ``doublet" layer of fibers with the centers of one of the single layers 
in the space between the fibers of the other single 
layer. There are eight doublet axial (aligned along the beam
axis) layers of scintillating fiber, as well as eight doublet stereo
layers that make a $\pm 3$ degree angle with the beam axis.
Table~\ref{tab-scifi} provides some more detail about each 
layer of the tracker. The outer (8th) layer is at the largest possible radius. 
The 7th layer is as close to the outer layer as is possible. The 
inner layer is at the least possible radius. 
The detector is divided into 80 sectors in phi. Each pie shaped 
slice has 960 fibers and the entire detector therefore 
has 76,800 channels.

\begin{table}[ht]
\begin{tabular}{ l  r  r  r  r } \hline \hline
Layer & Radius (mm) & Number of Fibers & Orientation & Pitch ($\mu$m) \\ \hline
1A    & 200.0       & 2560             & Axial       & 980.8          \\
1U    & 201.6       & 2560             & 3$^o$       & 987.7          \\
2A    & 249.1       & 3200             & Axial       & 977.2          \\
2V    & 250.7       & 3200             & -3$^o$      & 982.5          \\
3A    & 298.2       & 3840             & Axial       & 974.9          \\
3U    & 299.8       & 3840             & 3$^o$       & 979.1          \\
4A    & 347.3       & 4480             & Axial       & 973.2          \\
4V    & 348.9       & 4480             & -3$^o$      & 976.6          \\
5A    & 396.4       & 5120             & Axial       & 971.9          \\
5U    & 398.0       & 5120             & 3$^o$       & 974.7          \\
6A    & 445.5       & 5760             & Axial       & 970.9          \\
6V    & 447.1       & 5760             & -3$^o$      & 973.3          \\
7A    & 494.6       & 6400             & Axial       & 970.2          \\
7U    & 496.2       & 6400             & 3$^o$       & 972.2          \\
8A    & 519.6       & 7040             & Axial       & 926.1          \\
8V    & 521.3       & 7040             & -3$^o$      & 927.9          \\ 
         \hline \hline
\end{tabular}
\caption{Summary of D\O \ scintillating fiber tracker layers. The fiber pitch 
is adjusted so that the cylinders are completely covered  by the ribbons. }
\label{tab-scifi}
\end{table}

The scintillation light from the fibers is totally internally 
reflected down the length of the fiber. A connection is made at the 
edge of the tracker to  a clear fiber which transports the light to a 
solid-state light detector called a Visible Light Photon Counter (VLPC).
The number of photons available at the VLPC's,
for a charged particle which traverses through the center of a fiber, 
varies from 10 to 40, depending on the charged particle's pseudorapidity
and on attenuation due to the  distance from the clear fiber connector. 
D\O 's VLPC's are small silicon devices which 
have an array of eight photo sensitive areas, each 1 mm in diameter,
on their surface. They operate at temperatures from 6 to 15 Kelvin,
have a quantum efficiency of over 80\% and have a gain of
20,000 to 50,000.  The high quantum efficiency is important 
because of the low number of photons.

The momentum resolution depends on both 
the pseudorapidity of the charged track and its 
momentum. Simulations indicate the resolution, including information from
the silicon detector, is $\sigma(p_T)/p_T=\sqrt{0.015^2 \oplus (0.0014p_T)^2}$.
Fig.~\ref{fig-d0-trackres} shows the momentum 
resolution expected in Run~II for the scintillating fiber 
tracker combined with the silicon tracker.

\begin{figure}
\begin{center}
\epsfxsize=4.5 in
\epsfbox{d0-trackres.eps}
\end{center}
\caption{Momentum resolution of the D\O's combined scintillating fiber tracker
and silicon tracker systems.}
\label{fig-d0-trackres}
\end{figure}


\subsubsection{THE CDF CENTRAL OUTER TRACKER}

\begin{figure}
\begin{center}
\epsfxsize=2.9 in
\epsfbox{cdf_trklay.eps}
\end{center}
\caption{An $r-z$ view of the CDF tracking system showing the COT (8 outer
layers), the ISL (3 barrels at $r\sim 25$ cm), and SVX~II systems. }
\label{fig-cdf-trklay}
\end{figure}

CDF has also completely replaced their outer tracker, although they 
have chosen to replace it with a detector employing similar technology
to the open-cell drift chamber used in Run~I.  However, the original
CTC (``Central Tracking Chamber") had a maximum drift time
of 706~ns, far longer than the 396 or 132~ns bunch spacing planned 
for Run~II.  To avoid the problem of pileup from multiple interactions, and
because the original chamber had shown signs of aging, it
is being replaced with a completely new chamber, the Central
Outer Tracker or COT.  
Fig.~\ref{fig-cdf-trklay} shows an $r-z$ view of the new CDF tracking 
system. 

To operate the chamber without pileup at 132~ns, it has to
have a maximum drift distance of no more than about a centimeter,
roughly 1/4th that of the CTC. Even with the small pitch, a fast gas 
mixture containing 15\% CF$_4$ is required.  Additionally, constructing a
new tracking chamber gave CDF the opportunity to correct deficiencies
in the stereo reconstruction of the original chamber: the 
new chamber has 12 wires per stereo layer, the same as the
axial layers, rather than the CTC's six.  Details of the
COT's parameters are given in Table~\ref{tab-cot}.
\begin{table}[ht]
\begin{tabular}{l  r } \hline \hline
Number of Layers                       & 96 \\ 
Number of Superlayers                  &  8 \\ 
Stereo Angle by Superlayer ($^\circ$)  & +2,0,-2,0,+2,0,-2,0 \\
Cells per Superlayer                   & 168,192,240,288,336,384,432,480 \\
Sense Wires per Cell                   & 12 \\
Superlayer Radius (cm)                 & 46, 58, 70, 82, 94, 106, 119, 131 \\
Sense Wire spacing (mm)                & 7.62  \\
Wire                                   & $d=1.6$~mil gold-plated Tungsten \\
Tilt angle                             & $35^\circ$ \\
Active Length (m)                      & 3.1 \\
Total number of Wires                  & 73,080 \\
Drift Field $(k{\rm V}/{\rm cm})$      & 2.5-3  \\ \hline \hline
\end{tabular}
\caption{Summary of COT parameters.}
\label{tab-cot}
\end{table}

\begin{figure}
\begin{center}
%\epsfxsize=3.1 in
%\epsfbox{cdf-cot-cell.eps}
\epsfxsize=4 in
\epsfbox{cdf-cot-cell-new.eps}
\end{center}
\caption{Cell layout for CDF's Central Outer Tracker.  The cell
shown is for SL2, although the others are similar.}
\label{cdf-cot-cell}
\end{figure}

  The large number of wires required precludes simply
building a CTC with more wires. A scaled up CTC would have 
over 150,000 wires and would provide an endplate load of
over 100 tons.  Instead, the field shaping wires are
replaced with a field panel of gold plated 0.25 mil
Mylar stretched between two stainless steel wires 
traversing the length of the chamber, and attached at each
end by a G-10 board.  Between the field panels, sense
wires and potential wires alternate in a plane
(see Fig.~\ref{cdf-cot-cell}). Gold-plated tungsten 
wires are held into position by epoxying and soldering 
to a G10 board, which is then inserted as a unit to 
the COT where it is positioned by a precision milled
slot in the endplates  (see Fig.~\ref{cdf-cot-endplate}).
Such a design has several advantages: 

$\bullet$ Construction is simplified.  The necessary
precision of the device can be attained by using 
precision CNC milling of the endplates and using
keyways on each G10 board.  Because wires are 
wound on panels first, rather than strung individually,
an order of magnitude fewer pulls are necessary.

$\bullet$ Higher drift fields are possible.  This
allows for using a faster gas and having a smaller
drift time.  


\begin{figure}
\begin{center}
\epsfxsize=2.8 in
\epsfbox{cdf-cot-endplate.eps}
\end{center}
\caption{Endplate layout for CDF's Central Outer Tracker.  The locations
and sizes of the precision-milled slots are shown.}
\label{cdf-cot-endplate}
\end{figure}

  The 16,128 axial wires and 14,112 stereo wires
are read out in the following manner.  On the
chamber face, the signals are amplified, shaped and
discriminated by a custom ASD chip.  From there, the 
signals are sent in cables through the $30^\circ$ gap 
between the central and endplug calorimeters, received and
retransmitted by repeater cards mounted at the cable exit
point, and then the output of these repeaters sent 
to custom TDCs mounted in VME crates on the endwalls.  
The TDC's condense and latch hit information on a 
special mezzanine 
card, while buffering the full TDC readout in one of
42 Level 1 buffers.  The condensed data is multiplexed
and transmitted to the hardware track processor (the XFT,
or eXtremely Fast Tracker) in the counting room.  If
the event is accpeted by the trigger, the TDC's are read
out via a fast serial link.

   The absence of ADC's may make it appear that $dE/dx$
information is precluded, but in fact, the $dE/dx$ performance
is expected to be comparable or better than for Run~I.  The
charge deposited on a wire is encoded in the width of the
pulse by the ASD's.  The TDC's report both the leading edge and 
the pulse width, so this information can be used to calculate
$dE/dx$ offline, and use this information for particle 
identification.  Additionally, a barrel of 216 scintillator counters
is installed between the COT and the solenoid to provide 
time-of-flight information for found tracks.  The TOF not only
extends the particle identification to higher momenta, but
having two different and independent mechanisms to identify
particles allows for cross-calibration of the two methods.

\subsection{Silicon Inner Trackers}

The purposes of the silicon detectors are to identify tracks of charged 
particles which decay before they reach the outer tracker, to reconstruct
the decay vertices of $b$-hadrons, and to extend or improve the track-finding 
and momentum resolution. Because the proton and antiproton beams are very 
thin $(\sigma_{\rm transverse} < 50 \mu {\rm m})$ and because their transverse 
positions can be 
maintained very close to the center of the beampipe, a typical 
$b$-hadron decay vertex can be identified by the impact parameters of the 
tracks (~$300\mu {\rm m}$). This requires fine-pitched detectors oriented 
perpendicularly to the trajectories of the charged particles and mounted 
as close as practical to the decay vertices. The fine pitch and small radius 
necessary to achieve sufficient impact parameter resolution also 
improves the momentum resolution of the tracker systems.

Both D\O \ and CDF have undertaken ambitious silicon detector construction 
projects.

The accelerator parameters contribute to the design decisions. 
The interactions are spread out over a length  $\sigma_z=25$ centimeters, 
setting the length scale and motivating the detectors to have 
extended geometries.
The expected integrated luminosity implies a radiation dose of $\leq 1$ Mrad
during the life of the silicon detector. This, in turn forces the sensors and
readout chips to be radiation-hard and operated at cold temperatures, which
mitigates some of the adverse effects of radiation.

The basic detector design, common to both CDF and D\O, is the ``barrel 
geometry" comprised of layers of silicon detectors arranged in plates 
perpendicular  to the beampipe.  CDF and D\O \ have each improved on the basic
design by adding additional detectors to their systems. These design 
differences are the first of two ways that CDF's and D\O's silicon 
systems differ from each other (the second important difference is in the 
readout chip). In addition to measuring separated vertices 
and improving the momentum resolution, D\O \ chose to use silicon detectors 
to extend the tracking coverage to high pseudorapidity with disk-shaped 
assemblies comprised of wedge-shaped silicon wafers arranged in plates 
oriented perpendicular to the beamline. CDF, instead, chose to improve 
tracking resolution (especially in the forward region) by building a huge 
barrel geometry silicon detector at large radius.  In addition,
CDF chose to improve  the impact parameter resolution by installing a 
barrel layer (``Layer 00")  of silicon right onto the beampipe.  

\subsubsection{MECHANICAL CONSTRUCTION}

The D\O \ and CDF  barrel detectors are assembled from silicon wafers 
cut to rectangular shapes of the desired size and fastened, along with the 
associated readout electronics, to mechanical structures, called ``ladders", 
composed of beryllium wafers reinforced by composite-fiber + foam rails.  
The ladders are, in-turn, fastened to intricate precision-machined beryllium 
bulkheads. The disk-shaped bulkheads position and support the ladders at each 
end, and provide a cooled heat-sink for the electronics. The support structure
and cooling are made from light metals and composites to minimize multiple 
Coulomb scattering as particles pass through them.  

The D\O \ disks are assembled from wedges, similar to the ladders used in the
barrel, which support trapezoidal silicon wafers. The wedges 
are glued near their outer edge to a beryllium ring which supports them and
provides cooling for the silicon and for the readout electronics. 

Both the CDF and D\O \ barrel detector  assemblies and the smaller D\O \ disk 
assemblies are in-turn supported by a double-walled carbon-fiber/epoxy 
half cylinder which locates the silicon with respect to the outer tracker 
layers and also supports the cabling and cooling channels. 

\subsubsection{D\O \ SILICON DETECTOR} 
The D\O \ silicon detector~\cite{lipton}
consists of six barrel modules, twelve small 
disks (``F-disks"), and four large disks (``H-disks").
The mixed barrel/disk geometry provides silicon detectors arrayed at normal 
incidence, as is optimal for good tracking resolution, to charged particles 
with $|\eta |< 3$. 
Figure~\ref{fig-d0-silicon} shows the D\O \ silicon barrel modules with 
barrel detectors parallel to the beamline and disks perpendicular to the 
beamline. 

\begin{figure}
\begin{center}
\epsfxsize=4.5 in
\epsfbox{d0-silicon-new.eps}
\end{center}
\caption{D\O \ silicon. The figure shows the configuration of the six barrel 
modules, the 12 ``F-disks", and the 4 ``H-disks".}
\label{fig-d0-silicon}
\end{figure}

The six barrel modules are constructed with 4 layers of ladder assemblies 
with considerable overlap. Each barrel module is 12.4 cm in length and the
total length of the barrel is 76.2 cm.  The 4-layer coverage corresponds to 
the region $\eta=1.5$ for interactions at $z=0$.  Barrel layers one and three 
are constructed from double-sided silicon sensors with axial $(r-z)$ and 
$90^\circ$ stereo layers, except for the modules on each end of the barrel, 
modules one and six, 
which have single-sided axial strips.  Those are single-sided because 
stereo tracking is dominated by the information from the F-disks. 
Barrel layers two and four are constructed from double-sided detectors 
with axial and $2^\circ$ stereo layers in all six barrel modules. 
All of the detectors are AC-coupled to the readout electronics, described 
below. 
Table~\ref{tab-d0silbar} lists some details about the barrel layers.

\begin{table}
\begin{tabular}{ l r r r r } \hline \hline
Layer & Modules & Radius (cm) & Type \& pitch ($\mu {\rm m}$)  
                                          & Type \& pitch ($\mu {\rm m}$) 
                                                                  \\ \hline
1      & 1 and 6 & 2.7 to 3.65 & axial 50 & -                      \\
1      & 2 to 5  & 2.7 to 3.65 & axial 50 & $90^\circ$ 153          \\ 
2      & 1 to 6  & 4.59 to 5.51& axial 50 & $2^\circ$ 62.5          \\ 
3      & 1 and 6 & 6.6 to 7.53 & axial 50 & -                      \\ 
3      & 2 to 5  & 6.6 to 7.53 & axial 50 & $90^\circ$ 153          \\ 
4      & 1 to 6  & 8.6 to 9.43 & axial 50 & $2^\circ$ 62.5          \\ 
                                                                      \hline \hline
\end{tabular}
\caption{Parameters of D\O \ barrel silicon detectors. The axial detectors 
are made from p-type and the stereo layers from n-type silicon wafers. 
Modules one and six are located on the ends of the barrel.}
\label{tab-d0silbar}
\end{table}

The 12 ``F-disks" are comprised of 12 trapezoidal wedges arranged into a plate
with a hole for the beampipe. The active area inner radius is at 2.5 cm 
from the center of the beampipe and the outer is at 9.8 cm. 
The detectors are AC-coupled, double-sided, with strips angled
at $\pm 15^\circ$ with respect to the vertical. The pitch of the p-side and 
n-side detectors is $50 \mu {\rm m}$ and  $62.5 \mu {\rm m}$, respectively,
and the silicon wafers are 300 $\mu {\rm}$ thick.  Naturally, the strips are 
of different length depending on their location 
on the wedge. The six innermost F-disks attached to the outer sides of the 
six barrel modules. The three additional F-disks are attached to each 
outer side of the barrel assembly, with the effect of extending the acceptance
of the silicon system to higher pseudorapidity, especially for interactions
which occur at larger $z$. 

The four large ``H-disks" are located at $z=\pm 94$ cm and $z=\pm 126$ cm. 
The inner radius of the active area is at 9.6 cm from the center of the 
beampipe and the outer is at 23.6 cm. The detectors are AC-coupled, 
single-sided, with 40 $\mu {\rm m}$ pitch strips 
(pairwise readout makes the effective pitch 80 $\mu {\rm m}$)
angled at $\pm 7.5^\circ$
from the vertical. Each plane has wedges glued together back-to-back to 
provide a $15^\circ$ stereo angle. These forward disks are necessary to 
provide track stubs for forward particles which would otherwise exit the 
region of full solenoidal magnetic field without hitting the outer tracker.
They cover pseudorapidity ranging approximately $2\le |\eta| \le 3$. 

All of the detector types were tested~\cite{rocobeam}
 for radiation hardness at the 
8 GeV Fermilab Booster. They are expected to withstand a radiation dose 
greater than 1 Mrad.  The dose depends on the detector location and integrated 
luminosity. The innermost layer is expected to receive 0.5 Mrad/fb$^{-1}$.
The effect of the radiation damage is to increase the leakage current,
increase the bias voltage necessary for full depletion, and decrease the 
signal-to-noise ratio.  The effects are temperature dependent and can be
reduced by operating the detectors at low temperatures. The detectors 
will be operated at temperatures between $5-10^\circ$ C using a cooling
mixture of deionized ethylene glycol and water. 

The D\O \ silicon detectors are readout using the SVX~II 
chip~\cite{FNALTM1892}. SVX~II is a 128 channel, radiation hard CMOS chip
mounted directly on the ``High Density Interconnects" (HDI's), kapton-based 
flexible circuit, wire-bonded to the sensors at the ends of the ladders 
and wedges. Each of the 128 channels in an SVX~II chip features a 
preamplifier, a 32 stage analog pipeline with 4 $\mu {\rm s}$ delay, 
an 8-bit Wilkinson type ADC, and a latch-based sparsified readout. 
The chip is programmable for any interaction time from 132 to 396 ns. 
The pipeline depth, ADC ramp rate, preamplifier bandwidth, and thresholds 
are downloadable to each SVX~II chip.  

When a trigger signal is sent to SVX~II, data acquisition stops until the 
chip is completely read out.  The data can be readout in one of three 
different forms depending on the status of two control bits. If neither bit
is set then only the channels with digitized output above prespecified 
threshold (i.e. hit) are readout. If the ``Read Neighbors" bit is set
true, then hit channels and the channels immediately adjacent on each side 
are readout. This capability is daisy-chained across chip boundaries. 
The value of this capability is that it allows hit position interpolation with 
neighboring cells even if the neighbor cell didn't exceed threshold. 
If the ``Read All" bit is set, all channels are readout. This capability
is primarily for testing and calibration.

Connections to the outside world continue from the HDI's to 8-ft
long ``low-mass" cables which join the ends of the HDI's to unpowered 
``transition cards" mounted on the ends of the central calorimeter 
cryostat. Ultimately, these signals are gathered by a sequencer board 
connected by optical link to VME readout buffer electronics in the movable
counting house. The D\O \ silicon detector has 792,576 channels. 

\subsubsection{CDF SILICON DETECTOR} 

The upgrade provides the third generation of silicon detectors for CDF. 
In 1992, the sucess of the first generation, SVX, provided
CDF motivation to build a more radiation-hard version, 
 SVX$^{\prime}$ using AC-coupled silicon detectors and a 
radiation hard readout chip.  CDF calls the Run~II generation silicon 
system ``SVX~II" (not to be confused with the D\O \ silicon readout chip).  
In addition to SVX~II, CDF adds the ``Intermediate Silicon 
Layers", a large-radius barrel-geometry detector, and ``Layer 00", 
a small-radius barrel-geometry layer mounted directly on the beampipe. 

SVX~II consists of three barrel modules, each 29 cm long, but no disks. 
The barrels each have five cylindrical layers 
of ladders divided into 12 sections.  The silicon detectors are AC-coupled, 
double-sided. At a given radius, the ladders cover approximately $30\deg$ of 
azimuthal angle.  The silicon provides five $r-\phi$ 
measurements, three $r-z$, and two small-angle stereo measurements.  
Table~\ref{tab-cdfsilbar} lists some of mechanical specifications
about each barrel layer. Figure~\ref{fig-cdfbar} shows an end-view of the 
CDF SVX~II and the five cylindrical layers of ladders, and 
%Figure~\ref{fig-cdf-silicon} shows the entire silicon system.  
The two inner layers are mounted separately from the three outer layers 
so that inner layers are easily replaceable with $2 \mu {\rm m}$ 
repeatability. The readout chips, discussed below, are mounted on 
a BeO ceramic hybrid on or near the sensors and connected to flexible 
copper-kapton circuits (also called HDI's for High Density 
Interconnects). 

\begin{table}
\begin{tabular}{ l r r r r } \hline \hline
Layer & Radius (cm)     & Axial Pitch($\mu {\rm m}$) 
                                 & Stereo Angle & Stereo Pitch($\mu {\rm m}$) 
                                                                   \\ \hline
00     &  1.35 to 1.65   & 25    & NA           & NA               \\
0      &  2.54 to 3.00   & 60    & $90^\circ$   & 141              \\
1      &  4.12 to 4.57   & 62    & $90^\circ$   & 125.5            \\ 
2      &  6.52 to 7.02   & 60    & $+1.2^\circ$ & 60               \\
3      &  8.22 to 8.72   & 60    & $90^\circ$   & 141              \\ 
4      &  10.10 to 10.64 & 65    & $-1.2^\circ$ & 65               \\ 
                                                                      \hline \hline
\end{tabular}
\caption{Parameters of CDF's SVX~II and Layer 00 Silicon Detectors. }
\label{tab-cdfsilbar}
\end{table}

\begin{figure}
\begin{center}
\epsfxsize=4.2 in
\epsfbox{cdfbar.eps}
\end{center}
\caption{The CDF SVX~II silicon detector. The five radial layers 
(numbered 0-4) are 
shown supported by the bulkhead. The bulkhead outer radius (15), 
port-card (18), and cables (19) are
also indicated.  The bulkhead is supported by the carbon-fiber 
half-cylinder (21). The inset figure shows the beampipe outer radius (1), 
details of the beampipe connections (2-3), and the bulkhead inner radius (4).}
\label{fig-cdfbar}
\end{figure}

%\begin{figure}
%\begin{center}
%\epsfxsize=3 in
%\epsfbox{cdf_silicon.eps}
%\end{center}
%\caption{The CDF silicon detectors, SVX~II, ISL and Layer 00.}
%\label{fig-cdf-silicon}
%\end{figure}


The CDF ``Intermediate Silicon Layers" (ISL) detector is a large-radius 
barrel-geometry detector. With a radius of 20-28 cm, it is located between
SVX~II and the Central Outer Tracker. It is assembled from five barrel 
sections. Fig.~\ref{fig-cdf-trklay} shows the central ISL layer and two
of the four forward ISL layers. The central ISL layer, in the region
$|\eta| \le 1$, provides a tracking point important in connecting the 
tracks found in SVX~II with the tracks found in the COT. The forward
ISL layers, at radii 20 and 28 cm, enhance the 3D tracking in a fiducial
region, $1.0 \le |\eta| \le 2.0$, where the COT has incomplete layer 
coverage. This improves the track-finding efficiency and momentum resolution 
in that region. 

All of the ISL detectors are double-sided, AC-coupled, 
silicon that provides axial measurements and 
$1.2 ^\circ$ stereo measurements, both with strip 
pitch $112 \mu {\rm m}$. The detectors are mounted on ladders, which 
are are in turn mounted on Be ledges supported by a carbon fiber 
spaceframe. The spaceframe is mounted to the COT inner radius
via a piezo-electric ``inchworm" drives which allows for 
precise alignment of the silicon with respect to the beam
axis. The silicon detectors are radiation-hard but aren't 
expected to receive a large dose because of their radius. 
The resolution is expected to be $\le 32 \mu{\rm m}$ 
in $r-\phi$ and ($\le 1500 \mu{\rm m}$) in $z$. 

The Layer~00 detectors are single-sided axial silicon strips with a 
$25 \mu {\rm m}$ pitch at radius 1.35 to 1.65 cm. The overall length is 
the same as SVX~II. The purpose of Layer~00 is to improve the impact 
parameter resolution for low-$p_T$ particles (by providing a precise
measurement before substantial multiple scattering has occured)
and for other particles which 
pass through the readout electronics of SVX~II.  Layer~00 is mounted directly 
on the CDF beampipe. Because of the small radius the detectors will 
receive a radiation dose of $\sim 1 $ Mrad/fb$^{-1}$. The AC-coupled silicon 
is especially radiation resistant in that it can be operated with a bias 
voltage as high as 500 V. It must be maintained at $0^\circ$ C, which is
possible because the readout electronics is separated from the sensors, 
unlike SVX~II and the D\O \ vertex detector. The readout is ganged-by-two
with charge measurements, allowing $6 \mu {\rm m}$ hit resolution. 

The CDF silicon detectors are readout using the SVX3 integrated 
circuit~\cite{cdf-svx3}, similar to and derived from the SVX2 chip used
by D\O. SVX3 is a radiation hardened custom CMOS chip 
capable of operating at 396 ns and 132 ns bunch spacing.  
The key feature of SVX3 and a major 
difference between the CDF and D\O \ detectors is that 
SVX3 can continuously perform analog data acquisition in 
pipelined cells while bypassed cells are being readout. 
Thus it is effectively
deadtimeless for L1 trigger rates up to 50 kHz.
The Front-End (FE) section of the 
chip has 128 channels each with amplifier, charge integrator, and analog 
pipeline with a maximum depth of 42 cells. If SVX3 receives a L1 trigger, 
channels with hits during the appropriate crossing are bypassed from pipeline
operations until readout. The Back-End (BE) part of the chip contains 128 
channels each with a Wilkinson ADC, readout sparsification logic, readout 
FIFO, and output current drivers. It has the same three 
options for readout as described about D\O's SVX~II chip. 
CDF has 722,432 silicon 
channels readout by SVX3 electronics. Connections 
to the counting house are
similar to D\O's,  described above. 

% Pattern recognition and 3-d vertex reconstruction. Impact parameter 
% resolution $\sigma_{\phi}< 30 \mu{\rm m}$ and $\sigma_z<60 \mu{\rm m}$. 
% Radiation hardness. Mention single event upset. ????? 

\begin{table}[b]
 \begin{tabular}{ l  r  r } \hline \hline
                                          & CDF    & D\O \\ \hline
 Momentum resolution ($\delta p_T/p_T^2$) & 0.09\% & 0.14\%   \\
 %Momentum resolution ($\delta p_T/p_T$)   & -      & 
 %                      $\sqrt{0.015^2\oplus (0.0014p_T)^2}$ \\
 $\phi_0$ resolution (mR)                 & 0.3    &  similar  \\
 Impact parameter resolution ($\mu$m)     & 15     & 15  \\  
 $z_0$ resolution ($\mu$m)                & 30     & 150 \\ 
 $\cot(\theta)$ resolution                & $3.7 \times 10^{-4}$ 
                                                 & similar \\ \hline \hline
 \end{tabular}
 \caption{The tracking performance for the CDF and D\O \ silicon and outer 
 tracking detectors for high$p_T$ tracks.  Note that these numbers are 
 dependent on track position, angle and momentum, and so should be 
 viewed as approximate.}
\end{table}


