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Scientific Report 2007-2009
Particle physics
P2. Test and commissioning of the Muon Spectrometer of the ATLAS
experiment
The detection and the precision measurement of leptons,
in particular electrons and muons, is crucial for
large part of the ATLAS physics program. The muon
spectrometer of the ATLAS experiment is the part of the
detector aiming to identify muons coming from protonproton
collisions, reconstruct their trajectory with high
precision and measure their momenta. It consists of a
barrel and two end-caps air-core toroids instrumented
with three stations of precision chambers and trigger
chambers. A schematic overview of the spectrometer is
shown in Fig.1, where the names and the positions of the
different detectors are shown. The aim of the spectrometer
is to provide a measurement of the momentum for
muons with transverse momenta between few GeV and 1
TeV. It is designed to cover all azimuthal angles and polar
angles down to about 10 ◦ with respect to the proton
beam direction. The expected momentum resolution of
the muon spectrometer is evaluated by Montecarlo simulations
and is shown in Fig.2.
Contribution to resolution (%)
Total
12
Spectrometer entrance
10
8
6
4
2
0
10
Multiple scattering
Chamber Alignment
Tube resolution and autocalibration (stochastic)
Energy loss fluctuations
2
10
3
10
Pt (GeV/c)
Figure 2: Contributions to the expected momentum resolution
for muons reconstructed in the muon spectrometer as a
function of transverse momentum.
Thin gap
chambers
Radiation shield
MDT chambers
End-cap
toroid
Cathode strip
chambers
Resistive plate chambers
Barrel toroid coil
20 18 16 14 12 10 8 6 4 2 m
Figure 1: Side view of the ATLAS muon spectrometer. The
p-p collision point is in the origin of the twp-coordinate system.
The Sapienza University group in collaboration with
the INFN Sezione di Roma, has built and tested a significant
fraction of the MDT (Monitored Drift Tubes) chambers
composed by 3 cm diameter cylindrical drift tubes
assembled in layers. These chambers that allow to measure
the muon trajectories with a single-hit resolution of
less than 100 µm have been installed and commissioned
in the ATLAS detector and are now fully operational.
The Muon Spectrometer is completely working and
taking data since 2007. Cosmic ray data allow to monitor
the performance of the detector and to test the calibration
and alignment methods.
As shown in Fig.2, the main contribution to the
spectrometer resolution at high momenta comes from
the single MDT tube resolution and calibration. For the
continuous calibration of the MDT chambers, samples
of muon tracks identified by the trigger are sent to
three calibration centers where a complete calibration
procedure is done. One of these calibration centers is
in our University. In order to convert the raw time of
12 m
10
8
6
4
2
0
each single tube to the hit position, one needs first to
determine the t 0 of each tube and then to evaluate the
space-to-time relation between the measured time and
the drift distance. The calibration procedure allows
to obtain the t 0 of all the tubes and the space-to-time
relation for calibration regions where the tubes have
the same properties. The full procedure has been
extensively tested during the cosmic rays data taking
and is ready to be used during the LHC run. At the
same time the calibration data are used to study the
quality of the data and contribute to the global quality
assessment of the data taken.
References
1. G. Aad et al., JINST 3, S08003 (2008).
2. C. Adorisio et al., Nucl. Instr. and Meth. A593 232
(2008).
3. P. Bagnaia et al., Nucl. Phys. Proc. Suppl. 177 269
(2008).
4. C. Adorisio et al., Nucl. Instr. and Meth. A598 400
(2009).
Authors
F. Anulli 1 , P. Bagnaia, C. Bini, C. Boaretto, R. Caloi,
G. Ciapetti, D. De Pedis 1 , A. De Salvo 1 , G. De Zorzi, A.
Di Domenico, A. Di Girolamo, C. Dionisi, S. Falciano 1 ,
P. Gauzzi, S. Gentile, S. Giagu, F. Lacava, C. Luci, L.
Luminari 1 , F. Marzano 1 , G. Mirabelli 1 , A. Nisati 1 , E.
Pasqualucci 1 , E. Petrolo 1 , L. Pontecorvo 1 , M. Rescigno 1 , S.
Rosati 1 , E. Solfaroli Camillocci, L. Sorrentino Zanello, P.
Valente 1 , R. Vari 1 , S. Veneziano 1
http://www.roma1.infn.it/exp/atlas
Sapienza Università di Roma 109 Dipartimento di Fisica