Speaker
Oliver Kortner
(MPI Munich)
Description
The ATLAS muon spectrometer consists of three layers of precision drift-tube
chambers in an air-core toroid magnet system with an average field of 0.4 T.
The muon momenta are determined with high accuracy from the measure-
ment of the sagitta of the muon tracks in the three chamber layers. In
order
to achieve the required momentum resolution of the muon spectrometer of
bet-
ter than 4% for transverse momenta below 400 GeV/c and of 10% at 1
TeV/c,
the relative positions of the muon chambers are measured by a system of
op-
tical sensors with an accuracy of 30 μm. In order to verify the correctness of
the optical alignment, a method has been developed to measure the relative
chamber positions with muon tracks which are recorded during the
operation
of the experiment. For muons of pT < 40 GeV/c the momenta can be deter-
mined with high-enough precision independently of the relative
misalignment
of the chambers from the comparison of the local track direction measure-
ments in the individual chamber layers. This method allows for monitoring of
the chamber positions with an accuracy of about 30 μm in time intervals of
a
few hours during LHC operation.
During the operation of the experiment the chambers will be exposed to a
high flux of neutrons and γ rays which may lead to occupancies of up to
20%.
Even higher occupancies are expected for a possible luminosity upgrade of
the
LHC. We investigated on test-beam measurements at the Gamma-
Irradiation
Facility at CERN and Monte-Carlo data how pattern recognition algorithms
can cope with the increased hit rates.
Author
Oliver Kortner
(MPI Munich)
