Investigating the microscopic properties of strongly interacting matter with HADES

Abstract

Abstract:In the energy domain of 1-2 G V kinetic energy per nucleon, HADES has measured rare and penetrating probes in elementary and heavy ion collisions. Our results demonstrate that electron pair emission in C+C collisions can essentially be explained as a superposition of independent N+N collisions. HADES results on + − production in Ar+KCl collisions, however, show a strong enhancement of the dilepton yield relative to a reference spectrum obtained from elementary nucleon-nucleon reactions, signal the onset of medium effects beyond the superposition of individual N+N collisions. Intriguing results where also obtained from the reconstruction of hadrons with open and hidden strangeness. Analyses of the experimentally obtained hadronic yields measured in Ar+KCl allows to extract the chemical freeze-out conditions in the T -µ B phase diagram of strongly interacting matter. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double strange baryon Ξ − appears about ten times more abundant than expected. This result will be discussed in the context of the exploration of the nuclear matter phase diagram in the region of finite density. Further investigations to search for significant medium effects, will be followed over the coming years with an upgraded HADES detector. PACS

Strange Baryonic Resonances and Resonances Coupling to Strange Hadrons at SIS Energies

“…Provided that A+A collisions can be seen as the superposition of multiple nucleon-nucleon collisions, interferences could play a role in the total yield of some hadrons. But assuming that hadronisation follows the creation of an intermediate state of matter [15] in A+A collisions already in the GeV energy range the picture could be completely different and the effect of interferences completely negligible. It is clear that a better understanding of these processes is needed.…”

“…This measurement speaks in favour of the formation of an intermediate form of matter beyond a trivial superposition of nucleon-nucleon collisions followed by pion-nucleon and ∆-nucleon secondary reactions. Indeed, in case of a deconfined phase of matter the production of double strange baryon could proceed easier in a sort of catalytic mechanism as discussed in [15].…”