Dissertation / PhD Thesis

GSI-2021-01291

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Two-Pion Intensity-Interferometry in Collisions of Au+Au at √sNN = 2.41 GeV measured with HADES

Greifenhagen, R. A. H.

2021
Technische Universität Dresden Dresden

Please use a persistent id in citations: urn:nbn:de:bsz:14-qucosa2-737159

Abstract: In this thesis high-statistics π⁻π⁻ and π⁺π⁺ femtoscopy data are presented for Au+Au collisions at √sNN =2.4 GeV, measured with the High Acceptance Di-Electron Spectrometer HADES located at the heavy-ion synchrotron SIS18 at GSI.Due to space-momentum correlations the technique of intensity interferometry allows only to measure regions of homogeneity where pairs of particles with certain momentum origin. The determination of the space-time extent of the corresponding emission sources is then only possible via a comparison to models.The purpose of this thesis is to provide a multi-differential data set as input for such models and calculations, to draw conclusions from the total spatial and temporal extension of the pion emitting source. More than two billion events of the 45 % most central collisions are analysed. A complex data-driven pair cut is established to account for the close-track deficits in the non-trivial hexagonal geometry of the HADES setup. The correlation function is studied in the longitudinally co-moving system using the Bertsch-Pratt parametrisation. The region of homogeneity, parametrised as three-dimensional Gaussian distribution, is studied in dependence on pair transverse momentum, rapidity, azimuthal emission angle with respect to the event plane, collision centrality, and beam energy. For all centralities and transverse momenta, a geometrical distribution of ellipsoidal shape is found in the plane perpendicular to the beam direction with the larger extension perpendicular to the reaction plane. For large transverse momenta, the corresponding eccentricity approaches the initial eccentricity. The eccentricity is smallest for most central collisions, where the shape is almost circular.Furthermore, a tilt of the source w.r.t. the beam axis is found.The magnitude of the tilt angle of the emission ellipsoid in the reaction plane decreases with increasing centrality and increasing transverse momentum. All source radii increase with centrality, largely exhibiting a linear rise with the cubic root of the number of participants. A substantial charge-sign difference of the source radii is found, appearing most pronounced at low transverse momentum, which is addressed to the central Coulomb potential generated by the electrical charge of the participating nucleons in the collision. The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy.

Note: Dissertation, Technische Universität Dresden, 2021

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Contributing Institute(s):

1. HADES (HAD)

Research Program(s):

1. 612 - Cosmic Matter in the Laboratory (POF4-612) (POF4-612)

Experiment(s):

1. S407: Investigation of baryon rich dense nuclear matter by means of rare probes with HADES (POF3-612; HAD)

Appears in the scientific report 2021

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