Charged Pion Emission from 112Sn + 124Sn and 124Sn + 112Sn Reactions with the SπRIT Time Projection Chamber

Heavy ion collisions provide a probe of nuclear matter in extreme conditions. A particular area of interest is the density dependence of the symmetry energy term of the nuclear equation of state. The symmetry energy term describes the difference in binding energy between pure neutron matter and symmetric nuclear matter, which has an equal number of protons and neutrons. The density dependence of the symmetry energy affects the structure of neutron stars, which reach densities far exceeding what can be observed in the laboratory.The emission of charged pions from heavy ion collisions is expected to be sensitive to the symmetry energy at densities which are typically not otherwise observed in the laboratory. An experimental campaign to measure charged pion production was performed with the new SπRIT Time Projection Chamber, used in the SAMURAI spectrometer at RIKEN. The campaign included four secondary beams, produced from two primary beams. This work focuses on the measurement of pion emission from 124Sn + 112Sn and 112Sn + 124Sn systems, probing a single point of asymmetry at two center of mass energy points. This work serves to validate analysis methods, and to provide comparisons between the two experimentsThe development of the SπRIT Time Projection Chamber is discussed in detail, from design considerations to construction methods. Upgrades performed after the experimental campaign are also described. The entire experimental setup is described, with position measurements discussed and tabulated.The analysis of beam data from the BigRIPS fragment separator is described in detail, providing the beam PID, momentum, and angle on target. The absolute cross section is determined and a basic filter of impact parameter is implemented.We determine the pion spectra for 124Sn + 112Sn and 112Sn + 124Sn systems, comparing them to inform the range of pion kinetic energy which are consistently reconstructed for both systems. This informs the study of more asymmetric systems, where the pion ratio is expected to differ.