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The experimental program of the future Large Hadron Collider (LHC) at CERN, as
currently envisaged, has three components. The approved experiments,
ATLAS [1] and CMS [2], running at the
highest possible luminosity of
, will concentrate on rare,
large transverse momentum phenomena in the central rapidity region.
Two further experiments have been proposed but have not yet received final
approval. LHC-B [3] will study CP violation and B decays.
ALICE [4] will study heavy ion collisions.
It has, however, been recognized for some time that the next generation of
hadron-hadron colliders should fully exploit the intrinsic diversity of high
energy hadron collisions [5].
FELIX,
a full acceptance detector that will be capable of measuring almost completely
the energy- and particle- flow in pp collisions over the entire kinematic
range down to zero degree production angles
will thus pursue a
program of physics complementary to that of the other planned
experiments [6]. At
the most basic level, the argument for such a detector notes that interesting
physics is kinematically allowed for all pseudorapidities 
.
This is
illustrated in Fig. 1 in which the charged particle density
(photons are similar) and the energy flow, as predicted by Pythia [7],
are plotted as a function of the pseudorapidity. It is obvious that the
proposed detectors
such as ATLAS and CMS will miss most of the energy in generic pp collisions.
We thus regard the case for a full acceptance detector as compelling,
particularly since previous colliders (ISR, SPS, FNAL) were also deficient in
this respect.
Figure 1: Pseudorapidity distribution of charge particles and of the energy-flow.