Joint interdisciplinary publication of scientists from the Faculties of Physics and EiTI on effective modeling and visualization of the magnetic field in the ALICE experiment using GPU

(Top) Visualization of the traces in the Pb-Pb collision in the ALICE experiment using the Event Display program (source: CERN).

(Bottom) GPU simulated magnetic field model.

In the work entitled "Distributed simulation and visualization of the ALICE detector magnetic field" published in Computer Physics Communications (IF = 4.390, 140 points MEiN) team composed of M.Sc. Piotr Nowakowski (EiTI Faculty), Prof. Przemysław Rokita (Faculty of EiTI) and Dr. Łukasz Graczykowski (Faculty of Physics) shows how to use graphics cards to model the magnetic field in the ALICE experiment.

The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of two large magnets (solenoid and dipole), whose task is to bend the path of motion of particles, thanks to which it is possible to measure their momentum and charge. To precisely determine the parameters of the particles, the magnetic field must be measured with high precision. In 2005, the characteristics of the fields generated by both magnets were measured and a field model based on Chebyshev polynomials was created, which effectively operates on the CPU architecture without GPU support. This solution can be run on any machine. The experimental data made available to physicists for analysis are reconstructed in this way.

The 3D data visualization (Event Display) software, which is used to display the collected data live in the experiment control room (ALICE Control Room), does not use the Chebyshev polynomial model for particle propagation (which would make the software run slower). A simplified model of a homogeneous magnetic field generated by a solenoid is used (the dipole is not used at all), which translates into inaccurate visualization of the trajectory of the displayed traces.

The paper proposes the use of more advanced capabilities of graphics cards to use the Chebyshev polynomial model of the field to visualize particle trajectories. The future implementation of the proposed methods in the ALICE experiment software will allow the traces to be displayed much more accurately in the ALICE Event Display. Moreover, the proposed methods can also be implemented in other experiments, where the magnetic field is described by the Chebyshev polynomial model (e.g. the LHCb experiment).

Direct link to the publication (Open Access): 

Due to the fact that the work does not concern the analysis of physical data collected by ALICE from particle collisions provided by the LHC, the publication is not signed by all members of the ALICE collaboration, and only the members of the team that performed the research are co-authors.