Experiment Proposal - opera - Infn

Track segments on both the emulsion layers of the films are reconstructed from simulated data. The
two high resolution space points measured at the plastic base define the high precision (space) segments
used for tracking. A position smearing is introduced in order to simulate the measured angular resolution.
5.3 Reconstruction programs
A simple and modular framework for event processing has been developed. It includes specific unpacking
routines to handle data input in packed format and provides hooks for reconstruction submodules
in the various processing steps (run/event initialisation, data reading, processing, termination). Outside
the framework, submodules for reconstruction in the different subsystems (bricks, Target Trackers,
spectrometers) are available.
The software has been based so far on Fortran 77, with the support of CERN standard libraries
and runs on AIX and Linux platforms. The ZEBRA package is used for memory management and data
storage. A long term approach using modern OO-models under development for HEP simulation has
been tested to run on different platforms.
OPERA has joined the WIRED project for its event display. WIRED [72] (World Wide Web Interactive
Event Display) was created as an event visualisation framework inside a World-Wide Web browser.
It is written in Java using the Swing set for its graphical user interface. It is completely portable and
runs on any platform that fully supports the JDK (Java Development Kit 1.1 or better). The graphic
engine of WIRED handles both 2D and3D drawings. It supports multiple views and control widgets,
which interact with those views. It can access events and detector geometry data by using XML files. A
converter from GEANT 3.21 data into WIRED XML data is available.
5.4 Patternrecognitioninthetargetandinthespectrometer
A pattern recognition using target tracker scintillators has been developed following ideas implemented
for the NEMO experiment, called the cellularautomaton technique [73].
In each transverse detector projection one starts by building cells with two scintillator hits in two
consecutive planes. Then, one connects cells with a common extremity that do not make a large kink
between each other. Once the set of cells and their neighbours are known, one iteratively computes for
each cell its index along a possible track. All cells are initialised with an index value of 1. At each
iteration, each cell looks for neighbours in the upstream plane and increases its index by one unit if there
is a neighbour with the same index. The process stops when there are no more neighbouring cells with
the same index value.
The collection of track candidates starts from a cell with the highest index by adding its neighbours
with a lower index and so on. The selection of the best candidate is performed with simple criteria such
as the lowest mean value of the cosine between two consecutive cells or the lowest dispersion of the hits
around the straight line joining the two extremities of the track. When the best candidate is picked up,
its hits are removed and a new process of cell collection is performed.
The above algorithm considers the spectrometer as an extension of the target section. For example,
a reconstructed charm event is presented in Fig. 74.
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