ALICE (A Large Ion Collider Experiment) is the LHC (Large
Hadron Collider) experiment devoted to investigating the strongly
interacting matter created in nucleus-nucleus collisions at the LHC
energies. The ALICE ITS, Inner Tracking System, consists of six
cylindrical layers of silicon detectors with three different
technologies; in the outward direction: two layers of pixel
detectors, two layers each of drift, and strip detectors. The
number of parameters to be determined in the spatial alignment of
the 2198 sensor modules of the ITS is about 13,000. The target
alignment precision is well below 10 μm in some cases (pixels).
The sources of alignment information include survey measurements,
and the reconstructed tracks from cosmic rays and from
proton-proton collisions. The main track-based alignment method
uses the Millepede global approach. An iterative local method was
developed and used as well. We present the results obtained for the
ITS alignment using about 105 charged tracks from cosmic rays
that have been collected during summer 2008, with the ALICE
solenoidal magnet switched off.
The multiplicity of charged particles in the central rapidity region has been measured by the NA57 experiment in Pb-Pb collisions at the CERN SPS at two beam momenta: 158 A GeV/c and 40 A GeV/c. The value of dN ch /dη at the maximum has been determined and its behaviour as a function of centrality has been studied in the centrality range covered by NA57 (about 50% of the inelastic cross section). The multiplicity increases approximately logarithmically with the centre of mass energy.
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