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Scientific Report 2007-2009
Particle physics
P1. Commissioning of the ATLAS detector and preparation for the
data analysis
The Large Hadron Collider (LHC) at CERN extends
the frontiers of particle physics with its unprecedented
high energy and luminosity. Inside the LHC, bunches of
up to 10 11 protons will collide every 25 ns with an energy
of 14 TeV at a design luminosity of 10 34 cm −2 s −1 .
ATLAS is a general-purpose experiment, which consists
currently of 172 participating institutions with more
than 2900 physicists and engineers, including 700 students.
The detector, shown in Figure 1, consists of
an inner tracker inside a 2 T solenoid providing an axial
field, electromagnetic and hadronic calorimeters outside
the solenoid and in the forward regions, and barrel
and end-cap air-core-toroid muon spectrometers. The
precision measurements for photons, electrons, muons
and hadrons, and identification of photons, electrons,
muons, τ-leptons and b-quark jets are performed over
θ ≥ 10 ◦ . The complete hadronic energy measurement
extends over θ ≥ 1 ◦ . The trigger is performed using a
three-level system.
Luminosity [fb −1 ]
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2
1
0
significance
ATLAS
H → γγ
H → ZZ* → 4l
H → ττ
H → WW → eνµν
120 140 160 180 200 220 240 260 280 300
The detector design [1] has been optimized to cover
the largest possible range of LHC physics : searches for
Higgs bosons and alternative schemes for the spontaneous
symmetry-breaking mechanism; searches for supersymmetric
particles, new gauge bosons, leptoquarks,
quark and lepton compositeness indicating extensions to
the Standard Model and new physics beyond it; studies
of the origin of CP violation via high-precision measurements
of CP -violating B-decays; high-precision measurements
of the third quark family such as the topquark
mass and decay properties, and the decays of B-
hadrons. The expected performances for the standard
model Higgs boson search are shown in Figure 2.
In addition, to cope with the massive need for computing
infrastructure a world-wide computing network,
the World-wide LHC Computing Grid, has been built.
In the past the main contributions of our group have
been in the design and construction of the precision dem
H
[GeV]
Figure 2: Significance contours for different Standard Model
Higgs masses and integrated luminosities. The thick curve
represents the 5σ discovery contour. In the region below 2
fb −1 , the approximations are less accurate, but conservative.
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1
Figure 1: The ATLAS experiment.
tectors of the muon spectrometer, in the design and realization
of the muon trigger, in the high level triggers,
in data acquisition and in physics studies.
Currently, after an extensive programme of data acquisition
with cosmics particles, ATLAS is exposed to
the first LHC beams. Our interests now lie in the understanding
and commissioning of the detector (expecially
the parts built by us), in the calibration and processing of
the data and, expecially, in the first physics analyses. We
are engaged in Standard Model studies ([2], pag. 723),
in the search for the Higgs boson in its 4-lepton decay
([2], pag. 1243) and in exotic processes ([2], pag. 1695).
At present our group hosts 10 students for their Thesis
and 4 PhD students.
References
1. G. Aad et al., JINST 3, S08003 (2008).
2. G. Aad et al., Expected performance of the ATLAS
experiment : detector, trigger and physics (ISBN 978-92-
9083-321-5) (2008).
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 108 Dipartimento di Fisica