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Scientific Report 2007-2009<br />
Particle physics<br />
P1. Commissioning of the ATLAS detector and preparation for the<br />
data analysis<br />
The Large Hadron Collider (LHC) at CERN extends<br />
the frontiers of particle physics with its unprecedented<br />
high energy and luminosity. Inside the LHC, bunches of<br />
up to 10 11 protons will collide every 25 ns with an energy<br />
of 14 TeV at a design luminosity of 10 34 cm −2 s −1 .<br />
ATLAS is a general-purpose experiment, which consists<br />
currently of 172 participating institutions with more<br />
than 2900 physicists and engineers, including 700 students.<br />
The detector, shown in Figure 1, consists of<br />
an inner tracker inside a 2 T solenoid providing an axial<br />
field, electromagnetic and hadronic calorimeters outside<br />
the solenoid and in the forward regions, and barrel<br />
and end-cap air-core-toroid muon spectrometers. The<br />
precision measurements for photons, electrons, muons<br />
and hadrons, and identification of photons, electrons,<br />
muons, τ-leptons and b-quark jets are performed over<br />
θ ≥ 10 ◦ . The complete hadronic energy measurement<br />
extends over θ ≥ 1 ◦ . The trigger is performed using a<br />
three-level system.<br />
Luminosity [fb −1 ]<br />
10<br />
9<br />
8<br />
7<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
0<br />
significance<br />
ATLAS<br />
H → γγ<br />
H → ZZ* → 4l<br />
H → ττ<br />
H → WW → eνµν<br />
120 140 160 180 200 220 240 260 280 300<br />
The detector design [1] has been optimized to cover<br />
the largest possible range of LHC physics : searches for<br />
Higgs bosons and alternative schemes for the spontaneous<br />
symmetry-breaking mechanism; searches for supersymmetric<br />
particles, new gauge bosons, leptoquarks,<br />
quark and lepton compositeness indicating extensions to<br />
the Standard Model and new physics beyond it; studies<br />
of the origin of CP violation via high-precision measurements<br />
of CP -violating B-decays; high-precision measurements<br />
of the third quark family such as the topquark<br />
mass and decay properties, and the decays of B-<br />
hadrons. The expected performances for the standard<br />
model Higgs boson search are shown in Figure 2.<br />
In addition, to cope with the massive need for computing<br />
infrastructure a world-wide computing network,<br />
the World-wide LHC Computing Grid, has been built.<br />
In the past the main contributions of our group have<br />
been in the design and construction of the precision dem<br />
H<br />
[GeV]<br />
Figure 2: Significance contours for different Standard Model<br />
Higgs masses and integrated luminosities. The thick curve<br />
represents the 5σ discovery contour. In the region below 2<br />
fb −1 , the approximations are less accurate, but conservative.<br />
13<br />
12<br />
11<br />
10<br />
9<br />
8<br />
7<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Figure 1: The ATLAS experiment.<br />
tectors of the muon spectrometer, in the design and realization<br />
of the muon trigger, in the high level triggers,<br />
in data acquisition and in physics studies.<br />
Currently, after an extensive programme of data acquisition<br />
with cosmics particles, ATLAS is exposed to<br />
the first LHC beams. Our interests now lie in the understanding<br />
and commissioning of the detector (expecially<br />
the parts built by us), in the calibration and processing of<br />
the data and, expecially, in the first physics analyses. We<br />
are engaged in Standard Model studies ([2], pag. 723),<br />
in the search for the Higgs boson in its 4-lepton decay<br />
([2], pag. 1243) and in exotic processes ([2], pag. 1695).<br />
At present our group hosts 10 students for their Thesis<br />
and 4 PhD students.<br />
References<br />
1. G. Aad et al., JINST 3, S08003 (2008).<br />
2. G. Aad et al., Expected performance of the ATLAS<br />
experiment : detector, trigger and physics (ISBN 978-92-<br />
9083-321-5) (2008).<br />
Authors<br />
F. Anulli 1 , P. Bagnaia, C. Bini, C. Boaretto, R. Caloi,<br />
G. Ciapetti, D. De Pedis 1 , A. De Salvo 1 , G. De Zorzi, A.<br />
Di Domenico, A. Di Girolamo, C. Dionisi, S. Falciano 1 ,<br />
P. Gauzzi, S. Gentile, S. Giagu, F. Lacava, C. Luci, L.<br />
Luminari 1 , F. Marzano 1 , G. Mirabelli 1 , A. Nisati 1 , E.<br />
Pasqualucci 1 , E. Petrolo 1 , L. Pontecorvo 1 , M. Rescigno 1 , S.<br />
Rosati 1 , E. Solfaroli Camillocci, L. Sorrentino Zanello, P.<br />
Valente 1 , R. Vari 1 , S. Veneziano 1 .<br />
http://www.roma1.infn.it/exp/atlas/<br />
<strong>Sapienza</strong> Università di Roma 108 Dipartimento di Fisica