CERN-SPS. The NA61/SHINE collaboration studies at the CERN Super Proton Synchrotron (SPS) the onset
of deconfinement in hadronic matter by the measurement of particle production in collisions of nuclei
with various sizes at a set of energies covering the SPS energy range. This paper presents results
on inclusive double-differential spectra and mean multiplicities of PI- mesons produced in the 5% most central
7Be+9Be collisions at beam momenta of 19A, 30A,
40A, 75A and 150A GeV/c obtained by the so-called h- method
which does not require any particle identification.
Be+Be collisions can be characterized by the energy detected in the region populated by projectile spectators. Low values of this forward energy are referred to
central collision and a selection of collisions based on the
forward energy is called a centrality selection.
Although for Be+Be collisions the forward energy is not tightly correlated with
the impact parameter of the collision, the terms central and centrality are adopted following the convention widely used in heavy-ion physics.