NeuLAND - FAIR

Neutron with respect to proton/hydrogen flow at supra-saturation densities has been
already studied in 197 Au + 197 Au collisions with a combination of LAND and the FOPI
set-up for event characterization. In a re-analysis of the existing data-set and comparison
to predictions of the UrQMD [Li-05] and other transport models [Coz-11] it was
confirmed that in particular the elliptic flow observable is a sensitive measure of the
strength of the symmetry term in the nuclear matter EOS. These findings have initiated
a dedicated measurement of collective flows in collisions of 197 Au + 197 Au as well as 96 Zr
+ 96 Zr and 96 Ru + 96 Ru which has been carried out with the LAND detector coupled
to part of the CHIMERA detector array [Lem-09].
Because of the quadratically rising importance of the symmetry energy, the continuation
of this program with systems of larger asymmetry is very promising and important. The
reduced luminosities to be expected from the use of secondary beams and isotopically
enriched targets will require highly efficient detector setups.
A pre-requisite of such studies is to measure neutrons and protons within the same
phase space region. Hence, a neutron detector is needed with excellent calorimetric
characteristics augmented by a veto detector for charged particle identification. The
limited calorimetric capabilities of LAND allowed only for the separation of protons
from heavier hydrogen isotopes but has proven to be essential for such type of analyses.
Better calorimetric properties are highly desirable.
The neutron detector, typically placed near 45 ◦ for detecting mid-rapidity emissions for
the main part of the transverse-momentum spectra, should cover a maximum range of
polar angles in order to extend the measurements at given transverse-momentum to
forward and backward rapidities to measure directed and elliptic flow simultaneously.
This can be achieved by dividing the detector into two or more parts, placed at different
polar angles and used as separate detector units [Lei-93]. The distance to the target,
and with it the solid-angle coverage, will be determined by the capability of resolving
individual neutrons in high-multiplicity events. The improved efficiency of NeuLAND for
detecting neutrons in the 100 to 400 MeV energy range will be essential for extending
the program to reactions at lower energies for which significant mean-field effects are
predicted for directed and elliptic flows [Guo-11].
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