A schematic view of the kaon beam lines and of the detector layout is shown in
Figure 1. A 450 GeV/c primary proton beam with a nominal flux of
particles per pulse (ppp) impinges on a
Be target at a downward angle of 2.4mrad to produce the neutral 
beam.
A dipole magnet located downstream of the target station sweeps away the emitted
charged particles and deflects the remaining primary protons towards a Si
bent crystal. A small fraction ( 
) of these protons
are channelled by the crystal
and deflected back onto the beam line after passing through a
tagging detector. All other charged
particles are absorbed in a beam dump.
The resulting low-intensity
( 
ppp) proton beam is then
transported towards a second Be target for the production of the short-lived
kaons. The 
target is positioned 72mm
above the beam axis and 109m downstream of the bent crystal.
The proton beam strikes the
target at an angle of 4.2mrad. This production angle is chosen in
order to render the momentum spectrum of the detected as similar as
possible to the one over the 70-170GeV/c study range.
The
target is followed by a sweeping dipole magnet and a 6m long collimator
which defines a beam that converges towards the NA48 detector at a
downward angle of 0.6mrad. The end of the collimator coincides with
the last of a series of three defining collimators for the beam. Thus,
and decays can be produced simultaneously in almost
identical fiducial volumes.
The investigated decay region has a length of about 18m
and the corresponding ratio of to
decays into two pions is about 3. The
beginning of the kaon decay region is precisely defined by an anticounter
which detects all decays occuring upstream. The decay volume
lies inside a large, 90m long vacuum tank covered with seven rings of
scintillation counters to reject 
decays.
It is terminated by a thin kevlar window.
Figure 1: The NA48 Kaon beams.
The decay volume is followed by the NA48 detector which extends from
a distance of 216m to 255m downstream of the target. It
consists of
a magnetic spectrometer contained in a helium tank made of stainless steel
and closed by a 4mm thick aluminum endcap, a scintillator hodoscope
counter for triggering on charged decays, a photon detector
followed by a hadronic calorimeter and a muon veto detector. A vacuum
beam pipe with a 160mm diameter traverses all the detector elements to let the
neutral beam go through.
