NeuLAND - FAIR

8.1.2. Characterization of Neutron Interactions with the Full-Size
Detector
After the installation of the fully-equipped NeuLAND, again, a calibration experiment
will be performed. The above-mentioned technique of quasi-free scattering of deuteron
beams will be applied. Time resolution and efficiency of the full system will be determined,
the latter as a function of neutron energy. Using the full detector volume, it
allows in addition a detailed study of the event patterns for real one-neutron events.
This is an important input for the development of tracking algorithms in order to optimize
the recognition capabilities. The measured one-neutron response can be used in
order to simulate the response of NeuLAND to multiple neutron events by overlaying
several one-neutron hit-patterns, taken from experimental data. This method relies on
the superposition principle for hit patterns on the NeuLAND detector.
Moreover, NeuLAND will be exposed to real and clearly characterized two-neutron
events, using the breakup of tritons as detailed in the following. Tritons provide a clean
source of correlated two neutron events, where the intrinsic wave function is known with
high precision. Quasifree proton knockout on the tritons with coincident detection of the
two protons from the (p,2p) reaction enables us to put strict cuts on the reaction kinematics,
in particular the transferred momentum to the removed proton. By requiring a
momentum transfer considerable larger than the proton’s Fermi momentum inside the
tritons we enhance events where the two neutrons act as spectators in the reaction, and
thus keep their original correlations. Using the known n-n scattering length, also finalstate
interaction can be taken into account precisely. The n-n relative-energy spectrum
can thus be calculated reliably and compared to the observed spectrum. The response
of the detector to 2n events is particularly important for low relative energy between the
two neutrons, En−n, for which the efficiency drops rapidly. In addition, the incident CM
angle of the two neutrons can be determined by the measurement of the angles of the
two protons. This measurement will, thus, allow for a detailed check of the simulation
procedure for the two neutron response.
8.2. Cosmic Ray Tracking in NeuLAND for Adjustment and
Calibration
For the internal calibration of NeuLAND before, during and after experiments, tracks
from cosmic rays will be used. The hard component of the cosmic ray flux at sea
level, mainly muons (97%), has sufficiently high energy (mean energy is 2 GeV) to
penetrate the concrete ceiling of the Cave C or the R 3 B Cave, respectively, and to
traverse NeuLAND with approximately the speed of light. The expected rates of incident
cosmic rays amount to about 1.5 kHz. That enables a full scan of the detector within
reasonable time scales. The tracks of muons, as displayed in a GEANT4 simulation in
figure 8.4, serve as a good time reference between the traversed submodules.
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