Muon identification
Muons
are essential in most of the physics processes and can be used either for study
of signal events, for example Higgs decaying to 4 leptons, or as tag for
certain processes, for example processes that require b-quark identification(b-tagging).
Therefore muon identification presents an important issue in all the physics
topics we will concentrate on in the present RTN. Indeed, muons in a momentum
range between 5 GeV to 1 TeV are present in most of the channels of interest presented
in WP's 2-4.
In ATLAS the
MuonSpectrometer (MS) is composed of Tracking and Trigger detectors which span
a total area of 5600 m2, located inside the volume of an air core toroid
magnet, to minimize the effect of energy losses and multiple scattering. The
designed momentum resolution varies between 2Ð10 % for a momentum range between
5 GeV to 1 TeV. To achieve this momentum resolution in the spectrometer the
1200 individual tracking chambers -composed of drift tubes- were constructed
with a mechanical precision of better than 20 microns (the position of the
drift tubes in the chamber) while the position and deformation of individual
chambers is monitored to better
than 30 microns during data taking.
To maintain the designed momentum
resolution the following ingredients are needed :
á
Alignment
constants of individual chambers extracted from alignment
data recorded during data taking
á
Calibration
constants for the precise calculation of the distance of
minimum approach (r-t relation) of the muon tracks from the individual detectors
(drift tubes)
á
Energy
corrections due to energy losses of the muon in the 'dead'
material before the muon spectrometer and energy correction using the measured
energy loss in the calorimeters
á
Evaluation of the
performance of the muon spectrometer and optimization of
the track reconstruction efficiency. This evaluation is especially important
for BR measurements of rare processes and searches for new particles
A first
evaluation of the performance of the spectrometer is already accomplished using
muon test beam data at the CERN H8 test area where an octant of the ATLAS muon
spectrometer was installed together with samples of the inner tracker and
calorimeter modules of the final detector. With the first LHC data the
calibration and validation of the muon spectrometer will be done using
dedicated event samples from W and Z boson decays. The reconstruction of
the invariant mass of the Z-boson decaying to a pair of muons, will provide the
absolute scale calibration and a validation of the alignment and calibration
constants.
Participating institutes in the proposed RTN have played a central role in the design, construction
and test of the muon tracking and alignment systems and in the development of
the muon track reconstruction algorithm.
Therefore are expected to take in hand the muon
identification issues, which are crucial for the physics goals of this network.