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Überblick über das DØ-Experiment
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The Accelerator
DØ (D-ZERO) is
one of the two big experiments at the proton-antiproton collider TeVatron
at the Fermi National Accelerator Laboratory
(Fermilab) near Chicago. With it's length of 6 km, and particle collisions
with a centre-of-mass energy of 2 TeV, the TeVatron Collider is presently
the world's largest and most energetic accelerator.
Since March 2001, the upgraded Accelerator TeVatron is producing proton-antiproton
collisions in the DØ Detector. During a first period (Run IIa),
in which 2 fb-1 of data will have been collected, the luminousity
is expected to reach 2 x 1032 cm-2sec-1
with an average of 5.8 interactions per one crossing of the proton-antiproton
bunches [1].
The Goals
In comparison to Run Ib, which ended in 1995 (?), TeVatron
is expected to have increased it's luminosity by a factor of ~12. Mainly,
this is accomplished by enhancing the number of bunches from 6 to 36 and
by increasing the number of particles per bunch. Shortening the length
of each bunch significantly decreases the area of collisions in direction
of the beams, which improves the detector's resolution. In a planed Run
IIb, the luminosity will be increased furthermore with the aim of collecting
~ 15 fb-1 until the start of LHC
at CERN, Geneva.
Since the shutdown of the electron-positron collider LEP at CERN in
2000, where indications for the observation of the awaited Higgs Boson
have excited the whole scientific community, the focus of particle physics
has now moved towards the TeVatron with its two experiments CDF and DØ.
There are chances that the Higgs Boson could be observed beyond doubt and
the upgraded machines provide enough data to search for other so far unobserved
phenomena beyond the limits given by the four LEP
experiments.
The Challenge
As opposed to physics at lepton colliders such as LEP, p+p-
collisions have a large hadronic background, mainly from unwanted processes
from the spectator quarks and hadronic reactions from simultaneous collisions
within the same buch crossing. This results in a huge hadronic multiplicity
lying over the interesting physics events. Thus, the detection and identification
of leptons become even more important. Furthermore, high energetic electrons
and muons often are an indication of interesting physics processes and
therefore play a major role in the trigger system [2] where the Ludwig-Maximilians-University
takes action.
The Detector
The DØ
detector [3], which has also been substantially upgraded, was given
a new muon spectrometer for the forward region, constisting of three super-layers
of drift tubes and scintillator pixels. Each of the three layers is made
of multiple planes of muon tubes (four in the first, three in the second
and third super-layer) and an additional plane of plastic scintillators.
An azimuthal magnetic fieldof about 1.9 T in the iron yoke between the
first two layers allows the measurement of the momenta of the transversing
muons deflected in the magnetic field.
Schematic view of one quadrant of a forward layer of drift tubes as
seen in beam direction.
Frontal view of one quadrant of a forward pixel layer.
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Level 2 Myon Trigger
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In 2000, the Ludwig-Maximilians
Universität München joined, together with other German
institutes, the DØ collaboration. It took responsibilities for
the muon part of the Level-2 trigger system. This includes the development
of fast and efficient reconstruction software for the forward muon system
in order allow an expected rejection of 9/10 of incoming events with a
rate of up to 10 kHz.
In the DØ level-2 trigger, muon tracks are reconstructed using
the binary hit information (i.e. without drift time information) of the
drift tubes and the scintillator pixels in order to estimate the momenta
and the directions of the muons. This information is used in the global
level-2 trigger decision together with information from the inner tracking
systems and the calorimeters.
Possible hit scenario in the two outermost layers of the forward muon
system.
[1] Run
II Handbook.
[2] The DØ Collaboration, S. Abachi et al., The DØ
Upgrade: Forward Preshower, Muon System and Level 2 Trigger, Fermilab
FN-641 DØ, 1996
[3] The DØ Collaboration, S. Abachi et al, The DØ
Upgrade: The Detector and its Physics, Fermilab Pub-96/357-E, 1996
Tim Christiansen, last modified on
October 22, 2001
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