The investigation of the nuclear medium under extreme conditions of energy densities in relativistic heavy ion experiments (IMEN) - The new ROOT geometry package

ALICE is a general-purpose heavy-ion detector designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC of CERN. It currently includes more than 750 physicists and 70 institutions from 27 countries. Layout of the Alice detector is given. The detector is designed to cope with the highest particle multiplicities anticipated for Pb-Pb reactions (dN/dy ∼ 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are means of varying the energy density, and protons (both pp and p-nucleus), providing reference data for the nucleus-nucleus collisions. The new ROOT geometrical package is a tool designed for building, browsing, tracking and visualizing a detector geometry. The code works standalone with respect to any tracking Monte - Carlo engine, therefore it does not contain any constraints related to physics.The structure of the ROOT geometrical package is shown. However, the package defines a number of hooks in order to ease-up tracking, allowing user-defined objects to be attached to the basic architectural structures. The modeling functionalities were designed to optimize particle transport thorough complex geometries. The package is currently under development and new features will be implemented, but the basic functionality has already been extensively tested on several detector geometries. The final goal is to be able to use the same geometry for several purposes, such as tracking, reconstruction or visualization, taking advantage of the ROOT features related to bookkeeping, I/O, histograming, browsing and graphical interfaces. (authors)