Schild, Niklas (2018)
Reconstruction of e+e- in peripheral Au+Au collisions at sqrt sNN=2.42 GeV with HADES.
Technische Universität Darmstadt
Bachelorarbeit, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The investigation of hadronic matter in hot and dense conditions is a key research topic in the HADES collaboration and for many nuclear physicists around the world. To gain insight in the behaviour of strongly interacting particles, heavy ions are collided with relativistic speeds. Detection of particles created during a collision brings information about the properties of particles and eventually leads to a more detailed picture of the QCD phase diagram. e+e− pairs serve as a particularly interesting probe of the fireball as they do not interact strongly, but are influenced overwhelmingly by the electromagnetic force. Once created, through one of their many sources, this means that such dileptons can reach the detector directly and unhindered, such that they bring information about the early stages of the collision. Using the experimental data from 2012 Au+Au collisions at sqrt sNN = 2.42 GeV at HADES, these dileptons are identified and their invariant mass spectrum investigated. A particular focus is set on the inspection of peripheral events which have largely been ignored in previous works due to their limited statistics. This analysis includes an event selection, a single lepton identification and a subsequent signal extraction for which the combinatorial background is calculated. Furthermore, the signal is acceptance and efficiency corrected. On top of that, a normalisation to the number of π0 is applied and the excess pairs are isolated by subtracting reference and η-spectrum. This allows to calculate the excess yield and temperature from the remaining invariant mass spectra and their behaviour as a function of the mean number of participating nucleons is investigated.

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