CERN-THESIS-2012-153 26/07/2012 - CERN Document Server

Chapter 3
The LHC and the ATLAS Detector
3.1 Introduction
The Large Hadron Collider (LHC) at CERN near Geneva is the world’s largest and most energetic particle
accelerator. It has been designed to collide proton beams with a center-of-mass energy of up to 14 TeV, and a
nominal luminosity of 10 34 cm −2 s −1 . The high energy and luminosity of the LHC allows the study of a large
range of physics, from the precise measurements of known quantities to the exploration of physics beyond
the SM. Within this motivation, the ATLAS detector (A Toroidal LHC ApparatuS) has been designed as
a general purpose detector to probe proton-proton collisions and accommodate a very large spectrum of
physics foreseen at the TeV scale.
3.2 The LHC
The LHC is a two-ring, superconducting, hadron accelerator and collider installed in the tunnel 27 km in cir-
cumference initially built for LEP. Unlike how it is done in the Tevatron, the high beam intensities required
by the high luminosity exclude the use of anti-proton beams, and hence exclude the particle-anti-particle
collider configuration of a common vacuum and magnet system for both circulating beams. Therefore the
LHC is designed as a proton-proton collider with separate magnet dipole fields and vacuum chambers in
the main arcs and with common sections only at the insertion regions where the experimental detectors are
located [60,61].
One figure of merit in colliders such as the LHC is the luminosity:
L = N2 b nbfrevγr
F (3.1)
4πεnβ ∗
where Nb is the number of particles per bunch, nb the number of bunches per beam, frev the revolution
frequency, γr the relativistic gamma factor, εn the normalized transverse beam emittance, β ∗ the beta func-
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