Charged hadron production in central Ar+Sc collisions at the CERN SPS

Research Objectives The main goal of this work was to identify and obtain spectra of charged hadrons produced in Ar+Sc interactions at six beam momenta in the range of 13A-150A GeV/c. The project is a vital part of the NA61/SHINE programme, which main research goal is to study the collisions of intermediate systems, searching for the signatures of the onset of deconfinement and the critical point. Measured properties of hadron production in Ar+Sc collisions suggest that this particular reaction is on the boundary between "heavy" and "light" sys- tems. Ar+Sc may be the smallest of studied systems, in which colliding nu- cleons create not a number of isolated N+N events, but a collectively evolving fireball, with a possible formation of quark-gluon plasma at top SPS energies. Methodology Collisions of Ar+Sc were recorded in 2015 by the NA61/SHINE Collabora- tion. The work presented in this thesis involves the selection of events in terms of quality and physics relevance, identification of the most abundant charged hadrons and calculation of their kinematic spectra. The final results of this thesis deliver key information on the properties of π + , π − , K + , K − , p, and p̄ pro- duced in strong and electromagnetic interactions in the most central collisions of Ar+Sc. The spectra in transverse momentum and rapidity were measured for each of the listed particle species and mean multiplicities of charged kaons were calculated. Impact on studies of strongly interacting matter The project presented in this dissertation delivers important information on the influence of the sizes of colliding ions on the properties of hadron pro- duction. In particular, the measurement of strangeness production (K + /π + ) in Ar+Sc establishes a puzzling system size dependence, that none of the com- monly used theoretical models can reproduce, therefore motivating further phenomenological studies. Similarly, measured longitudinal spectra of protons and anti-protons provide interesting input for studies of the equation of state in a baryon-rich medium. Broader knowledge about system size dependence of hadron production properties will surely bring important insight into the basic properties of