Programs development and computing for the offline analysis of Multi Purposes Detector (MPD) experiment at NICA collider are considered. Detailed detectors simulation of the MPD and event generation with Monte Carlo methods are very important in the experimental analysis for the determination of the detector acceptance and resolution, and to distinguish background event with known processes from new physics. Support of the interactive graphical presentation of simulated and experimental data at all levels, from the event display are shown also.
Recently a few experiments for heavy-ion physics are being prepared to work at the NICA collider, which will come into operation soon. Three detectors MPD, BM@N and SPD with many complex components will be used in these experiments, which are performed by large international collaborations with a few hundreds of physicists. The lifetime of the experiments will be more than tens years, as usual. With typical event rates of a few KHz and size of each event about hundreds of KB, the raw data will be of the order of 10 PB per year. So the software and computing systems for experiments at NICA collider need to cover a broad range of activities including the design, evaluation, construction, and calibration of the detector before the experiment start and then, the storage, access, reconstruction, analysis of data with the support of a distributed computing infrastructure for physicists engaged in these tasks during experiment runs.
The main objectives of the HEP experiment computing frameworks are the simulation of the primary interactions with the realistic detector response and the reconstruction and analysis of the data coming from simulated and real interactions. For NICA experiments the frameworks inherited from the FAIRRoot framework [1] are used.
The frameworks for each experiment of the NICA project: MPD, BM@N and SPD, named as MPDRoot, BMNRoot and SPDRoot correspondingly. They differ only with description of different sets of detectors. These frameworks have the same structure and use the same external programs included in the FAIRsoft package. FAIRsoft package includes external packages for the software development like BOOST, GSL, GEANT4 (3), Millepede and ZeroMQ. All of these packages are free, available under the LGPL license and works at different flavors of Linux operational systems.
The above listed MPD detectors have a complicated geometry. For the geometry description of
whole detectors of MPD experiment the GEANT4 package [3] was used. This package allows one to
make a simulation of the geometry and response on particle interactions in each detector. The geometry
simulation of the detectors for the 1-st stage of the MPD experiment is shown on the Fig. 1. Also, the
table I presents geometry version and response elements of listed detectors. For more detailed simulation
of the the TPC other package, Garfield [
Monte Carlo generators, used for simulation of nuclei-nucleus collisions at NICA energies for MPD experiment are listed in table II. The simple generators were used for the developments of the reconstruction programs and for the simulation of detector responses but few of them can be also used for the investigation the feasibility of some physics signatures.
Fig.2. MPD MC events DB
To work with these relative data for the NICA experiments it plans to use the open source relational database PostgreSQL.
Event display programs are the useful tools in high energy physics experiments. Usually event display programs are solid, stand-alone programs, special for each experiment; there may be even two or more specialized event display programs in a single big experiment. For the MPD the new interactive 3D Web event display was developed with very detailed simulation of detector geometry and responses. On the Fig. 3 shown the sensitive volume of TPC with MC points, hits and reconstructed tracks. Also projections of the hits on endcap pad planes are visible.
The storage, networking and processing power needed to analyse data of NICA experiments is well in excess of LHEP and LIT computer facilities and exceed any reasonably projected capabilities of JINRs computing systems in the future.
The offline data processing of MPD experiment at NICA collider are presented. Frame-work for simulation MPD experiment and general data analysis for simulated and experimental events is available now. Many other important task also are solved for MPD experiment: TPC alignment algorithm, Web interactive event displays for other MPD detectors, calibration task for MPD TPC and others.
The authors are grateful to the members of Laboratory of Information Technologies for help in the MPD software development and for implementation of "DIRAC" interware in the JINR computing resources. The authors would like to thank Dr. Kuzmin V.A. for help in developing some algorithms.
This work was supported by grant of Russian Foundation for Basic Research № 18-02-40102. [1] FaiRoot framework, available at https://fairroot.gsi.de/ [2] MpdRoot framework, available at https://mpdroot.jinr.ru [3] Allison, J et al. Recent developments in Geant4 // NIM A vol. 835 p. 186