Abstract
The ATLAS (A Toroidal LHC Apparatus) detector was tested with cosmic rays prior to the start of full operation of the Large Hadron Collider (LHC) in 2008. During the commissioning phase, the development of specialized tools for efficient cosmic ray data analysis is essential. A key requirement for final analysis is the ability to visualize cosmic muon tracks and the corresponding activated cells in the detector, enabling visual verification of data coherence and identification of potential issues. This work presents a 3D visualization tool for cosmic muon track reconstruction based on activated cells in the highly segmented ATLAS calorimeter system. The tool was developed using the ROOT framework, allowing seamless integration with analysis tools used by the ATLAS community. It employs the ROOT embedded geometry package to model the calorimeter structure at the cell level and provides routines to populate cells with reconstructed data. User-defined energy thresholds can be applied to display only relevant information. The structure of the tool and application examples using reconstructed data are presented.