Mathematical modeling and information support
of experimental investigations

Data processing support in particle physics. The main works were related to the development of basis resources (both the tool and target computing) of experiments in high-energy physics. The main gains were directed to the development and installation of the system for processing experimental and simulated (Monte-Carlo) data of the EXCHARM experiment on the new powerful server of the Linux-cluster RISK. It should be noted that in scales, entirety, comprehensive approach and level of the scope of the problems, this trend, connected with the creation and application of the Data Processing System, is very important.

The experience and methodical results obtained in the EXCHARM experiment are applied in other experiments, including those with JINR participation at CERN, etc. [1].

Development of new methods for data processing. One of perspective methods of the analysis of experimental data is a wavelet analysis based on a wavelet transformation.

The WASP (Wavelet Analysis of Secondary Particles angular distributions) package was developed. It is a C++ program aimed to analyze secondary particles angular distributions in high-energy nucleus-nucleus interactions. (WASP was designed for data analysis of the STAR and ALICE experiments). WASP provides a user-friendly Graphical User Interface (GUI) implemented by using ROOT GUI classes.

The first version of WASP was successfully applied to data analysis. Angular distributions of secondary particles produced in the interactions of sulphur and oxygen nuclei with photoemulsion nuclei at energies of 200 and 60 GeV/nucleon were analyzed. With the help of the wavelet analysis it was observed that the pseudorapidity distributions of the particles summed over all the events had three sub-structures. The distributions in separate events have more than one sub-structure in 40 % of the cases. The wavelet analysis allows one to separate events with different sub-structures (Fig. 4) [2]. New WASP version makes it possible to perform both one- and two-dimensional wavelet analysis. Thus it can be used for detecting ring-like structures [3-7].



Fig. 4. Shower particles pseudorapidity distribution in events
with nS < 25 (a) and its wavelet spectrum (b).
Three sub-structures arise at scale 0.4

A study of software efficiency improvements for the pattern recognition chambers (PC) of the HERA-B outer tracker (OTR) has been accomplished in framework of the planned LPP's activity in the HERA-B collaboration. A new version of the PC calibration program was developed on the basis of the consistent applying of the robust approach to both: track-finding algorithms and calibration function calculation. In addition to the improvement of the calibration accuracy, it allowed one to accelerate the calibration procedure by an order of magnitude in comparison to the conventional calibration program. The most effective was the robust fit of cubic splines directly to raw data which are the many thousands of the drift time measurements. The fit results are shown in Fig. 5.



Fig. 5. Results of the cubic spline fit to 5 mm PC drift data

In cooperation with LHE the experimental data on proton and -meson rapidity distributions in interactions at 3.36 GeV/nucleon in the events with different multiplicities of production of mesons was compared with predictions of RQMD and FRITIOF models. It was shown that the RQMD model reproduces satisfactorily the -mesons distributions, but unsatisfactorily describes the protons characteristics. The modified FRITIOF model gives good results at tuning the free parameters of the model [8].

Processing of experimental data for determination of exotic states of hadron structures has been completed. Experimental observations of the anomalous-narrow resonant hadronic structures (1630), N(3520), (3170) are discussed. These supposed exotic states are produced in the processes with large 4-momentum transfers. The special feature of the decay points out a space clusterization of colourless decay products of (1630) and N(3520), their angular separation in two parts [9].

Application of the method of volume and boundary integral equations in models of magnet systems with superconducting shields. The modeling of magnet systems with superconducting shields has been considered. Nonlinear volume and boundary integral equations are derived that govern the magnetization distribution over a nonlinear medium and the current distribution over the superconductor boundary. Methods for discretization of the continuous equations and for iterative solving of the nonlinear systems thus obtained are suggested. The results of a simulation of the magnet system employed in the ALICE experiment (CERN) are presented [10].

Application of the mathematical modeling in low- and intermediate-energy physics. Using the model of a temperature peak as well as the measured radii of tracks in a high-temperature superconductor and its thermal characteristics, an effective electron-phonon relaxation time has been calculated for this material. It was in a good agreement with experimentally measured (by methods of laser technique) values of this magnitude. Thus, for the first time, a self-consistent description of the process of track formation in the high-temperature superconductor, not containing any matching parameters, has been constructed [11].

A new approach to the local curve approximation and the smoothing has been proposed. A very simple in computing and stable to random errors cubic smoother in an adaptation mode (LOCUS) is constructed. The efficiency and the noise stability of the algorithm are confirmed by examples and by comparison with other known non-parametric smoothers [12].

Parameters of a subcritical cascade reactor driven by a proton accelerator and based on a primary lead-bismuth target, main reactor constructed analogously to the molten salt breeder reactor (MSBR) core and a booster-reactor analogous to the core of the BN-350 liquid metal cooled fast breeder reactor (LMFBR) have been estimated. It is shown by means of Monte-Carlo modeling that the reactor under study provides safe operation modes (keff = 0.94-0.98), is capable of transmuting effectively radioactive nuclear waste and reduces by an order of magnitude the requirements on the accelerator beam current. Calculations show that the maximal neutron flux in the thermal zone is 1014 cm2 s-1, in the fast booster zone is 5.12*1015 cm2 s-1 at keff = 0.98 and proton beam current I = 2.1 mA [13].

© Laboratory of Information Technologies, JINR, Dubna, 2002
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