Ricerca CERCA

Automatic recognition of particle tracks in nuclear scattering

azienda Thesis in external company    


Research Groups GR-09 - GRAphics and INtelligent Systems - GRAINS

Thesis type THESIS W/ RES. CEN.

Description Reconstruction of the complete kinematics of a collision between particles at accelerators is a fundamental step in the investigation of subtle processes hidden in the 10-15 m and 10-23 s space-time windows where the interaction takes place.

At the Joint Institute for Nuclear Research (JINR) (Dubna-Russia) a set of several thousand pion - Helium nucleus scattering events has been observed with a detector, namely a self-shunted streamer chamber (SSSC) filled with Helium, capable of revealing the complete interaction kinematics, down to the momenta of very low-energy charged secondary interaction products such as protons with an energy of merely 1 MeV. A charged particle leaves along its trajectory electron-ion pairs, that give rise to electric discharges in their initial stage (streamers), produced when a high-voltage pulse is applied to the SSSC electrodes, if a signal from scintillation counters reveals a nuclear event to have occurred inside the chamber volume. The visible light, emitted in excitation and ionization processes taking place within the streamers in the Helium gas filling the volume of the detector, indicates the particle tracks and is captured by two CCDs and saved in two photograms. The kinematics (the momenta of particles that take part in the collision) is reconstructed from the analysis of the tracks left by charged particles.

This thesis will focus on the automatic recognition of particle tracks in nuclear scattering events taken by the PAINUC experiment at the JINR phasotron (particle accelerator) of the Laboratory of nuclear problems (LNP).

A purpose of this thesis consists in the determination of distributions of various kinematic parameters (such as particle momenta, energies, effective masses etc.) of intermediate-energy pion Helium nucleus events for possible revelation of subtle processes between nucleons in the Helium nucleus. To this end the thesis work will be focused on automatic 3D reconstruction of the trajectories (tracks) of initial and secondary particles pertaining to nuclear interaction events occurring in the LNP self-shunted streamer chamber (SSSC) filled with Helium. Over 30 thousand such events have been collected during runs of the SSSC in pion beams of the LNP phasotron. Pion Helium nucleus events were photographed using CCDs that registered visible light emitted by excited helium atoms in streamers along particle tracks; the light is gathered in voxels (3D pixels). Identification of the tracks will be followed by the determination of a set of fundamental parameters characterizing the interactions: the vertex (where the pion Helium nucleus scattering occurred) and the best fitting functions for describing the identified tracks (typically a 3D helix of variable radius). The system will also provide for the identification of non-interacting particles and other noise sources. The task will be achieved by applying both standard pattern recognition algorithms (i.e. Cellular Automata) and AI-based approaches. The efficiency of the automatic identification algorithm will be essential for the subsequent analysis of the physics phenomena hidden in the scattering event kinematics as well as for providing a powerful didactic tool for introducing nuclear and particle physics to students and the general public.

The thesis will be developed in collaboration with CERN, JINR and DISAT.

See also  http://grains.polito.it/work.php

Deadline 12/08/2022      PROPONI LA TUA CANDIDATURA

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