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\title{A Brief Description of the D\O\ Detector in Run II} 
\author{T. Ferbel} 
\date{\today}

\begin{abstract} The text below provides a minimal and a longer description of the main elements of the D\O\ Detector in Run II of the Tevatron. It is intended as a rough template for insertion into our papers on data analysis. Clearly, different analyses will emphasize different aspects of the hardware, and you should therefore feel free to modify the wording and any technical details. In fact, you are encouraged to modify the text somewhat to avoid issues of plagiarism.
\end{abstract}

\maketitle

\leftline{\bf{\sc Minimal Description:}}
The D\O\ detector has a central-tracking system, consisting of a 
silicon microstrip tracker (SMT) and a central fiber tracker (CFT), 
both located within a 2~T superconducting solenoidal 
magnet~\cite{run2det}, with designs optimized for tracking and 
vertexing at pseudorapidities $|\eta|<3$ and $|\eta|<2.5$, respectively.
{\em Optional: Central and forward preshower detectors are positioned just outside of 
the superconducting coil.} A liquid-argon and uranium calorimeter has a 
central section (CC) covering pseudorapidities $|\eta|$ up to 
$\approx 1.1$, and two end calorimeters (EC) that extend coverage 
to $|\eta|\approx 4.2$, with all three housed in separate 
cryostats~\cite{run1det}. An outer muon system, at $|\eta|<2$, 
consists of a layer of tracking detectors and scintillation trigger 
counters in front of 1.8~T toroids, followed by two similar layers 
after the toroids~\cite{run2muon}. 
{\em Optional: Luminosity is measured using plastic scintillator 
arrays placed in front of the EC cryostats. The trigger and data 
acquisition systems are designed to accommodate the high luminosities 
of Run II.} 

\vspace*{0.5cm}
\leftline{\bf{\sc Longer Description:}}
The D\O\ detector consists of a magnetic central-tracking system, 
comprised of a silicon microstrip tracker (SMT) and a central fiber 
tracker (CFT), both located within a 2~T superconducting solenoidal 
magnet~\cite{run2det}. The SMT has $\approx 800,000$ individual strips, 
with typical pitch of $50-80$ $\mu$m, and a design optimized for 
tracking and vertexing capability at pseudorapidities of $|\eta|<2.5$. 
The system has a six-barrel longitudinal structure, each with a set 
of four layers arranged axially around the beam pipe, and interspersed 
with 16 radial disks. The CFT has eight thin coaxial barrels, each 
supporting two doublets of overlapping scintillating fibers of 0.835~mm 
diameter, one doublet being parallel to the collision axis, and the 
other alternating by $\pm 3^{\circ}$ relative to the axis. Light signals 
are transferred via clear fibers to solid-state photon counters (VLPC) 
that have $\approx 80$\% quantum efficiency.

Central and forward preshower detectors located just outside of the
superconducting coil (in front of the calorimetry) are constructed of
several layers of extruded triangular scintillator strips that are read 
out using wavelength-shifting fibers and VLPCs. The next layer of 
detection involves three liquid-argon/uranium calorimeters: a central 
section (CC) covering $|\eta|$ up to $\approx 1.1$, and two end
calorimeters (EC) that extend coverage to $|\eta|\approx 4.2$, all 
housed in separate cryostats~\cite{run1det}. In addition to the preshower 
detectors, scintillators between the CC and EC cryostats provide 
sampling of developing showers at $1.1<|\eta|<1.4$.

A muon system~\cite{run2muon} resides beyond the calorimetry, and consists of a 
layer of tracking detectors and scintillation trigger counters 
before 1.8~T toroids, followed by two similar layers after
the toroids. Tracking at $|\eta|<1$ relies on 10~cm wide drift
tubes~\cite{run1det}, while 1~cm mini-drift tubes are used at
$1<|\eta|<2$.

Luminosity is measured using plastic scintillator arrays located in front 
of the EC cryostats, covering $2.7 < |\eta| < 4.4$. A forward-proton 
detector, situated in the Tevatron tunnel on either side of the 
interaction region, consists of a total of 18 Roman pots used for 
measuring high-momentum charged-particle trajectories close to the 
incident beam directions.

Trigger and data acquisition systems are designed to accommodate 
the high luminosities of Run II. Based on preliminary information from 
tracking, calorimetry, and muon systems, the output of the first level 
of the trigger is used to limit the rate for accepted events to 
$\approx$ 2~kHz. At the next trigger stage, with more refined 
information, the rate is reduced further to $\approx$ 1~kHz. These
first two levels of triggering rely mainly on hardware and firmware.
The third and final level of the trigger, with access to all the event 
information, uses software algorithms and a computing farm, and reduces 
the output rate to $\approx$ 50~Hz, which is written to tape.


\begin{thebibliography}{99}
  \bibitem{run2det} D\O\ Collaboration, V. Abazov {\it et al.}, ``The Upgraded D\O\ Detector", in preparation for submission to Nucl. Instrum. Methods Phys. Res. A.

  \bibitem{run1det} D\O\ Collaboration, S. Abachi {\it et al.}, Nucl. Instrum. Methods Phys. Res. A {\bf 338}, 185 (1994). 

  \bibitem{run2muon} V. Abazov {\it et al.}, ``The Muon System of the Run II D\O\ Detector", physics/0503151.

\end{thebibliography}

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