Seminarium "Teoria cząstek elementarnych i kosmologia"
sala 1.01, ul. Pasteura 5
2020-01-23 (12:15) 
Piotr Salabura (UJ)
Studying QCD matter with virtual photons
Real and virtual photons decaying into dilepton pairs are unique probes to study microscopic properties of QCD matter produced in energetic heavy ion reactions. As they do not undergo the strong interaction and thus their mean free path is much longer than the size of hot and dense fireball created in such collisions, they carry out undisturbed information about temperature of the early phase of reaction and microscopic properties of its constituents. The latter ones are strongly connected to properties of light vector mesons acting as interpolating field between hadrons and photons.
In experiment, radiation of such pairs can be identified as the excess in the invariant mass of spectrum of dilepton pairs above the “cocktail” of known hadronic decays at the freeze-out of reaction. Such excess have been observed in various experiments from low energy SIS18 (√s ∼ 2 GeV) to top RHIC energies (√s ∼ 200 GeV) and recently also at LHC. The observed distributions are consistently described by a thermal-like emission from the fireball with an average temperature higher than the one concluded from hadron spectra. The distributions indicate strong melting of rho meson in hot and dense matter, the effect which is discussed in context of chiral symmetry restoration. In the talk review of experimental results and interpretations on aforementioned aspects will be given with special focus on recent results of the HADES experiment [1].
[1] Nature Phys. 15 (2019) no.10, 1040-1045]
In experiment, radiation of such pairs can be identified as the excess in the invariant mass of spectrum of dilepton pairs above the “cocktail” of known hadronic decays at the freeze-out of reaction. Such excess have been observed in various experiments from low energy SIS18 (√s ∼ 2 GeV) to top RHIC energies (√s ∼ 200 GeV) and recently also at LHC. The observed distributions are consistently described by a thermal-like emission from the fireball with an average temperature higher than the one concluded from hadron spectra. The distributions indicate strong melting of rho meson in hot and dense matter, the effect which is discussed in context of chiral symmetry restoration. In the talk review of experimental results and interpretations on aforementioned aspects will be given with special focus on recent results of the HADES experiment [1].
[1] Nature Phys. 15 (2019) no.10, 1040-1045]