# Quark Matter 2018

13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

## Multi-differential pattern of low-mass e+e- excess from 2.42 GeV Au+Au collisions with HADES

14 May 2018, 17:30
20m
Sala Casinò, 1st Floor (Palazzo del Casinò)

### Sala Casinò, 1st Floor

#### Palazzo del Casinò

Parallel Talk Electromagnetic and weak probes

Szymon Harabasz

### Description

The matter formed in central heavy-ion collisions at a few GeV per nucleon is commonly understood as resonance matter, a gas of nucleons and excited baryon states with a substantial contribution from mesonic, mostly pionic excitations. Yet, in the initial phase of the reaction the system is compressed to beyond nuclear ground state density and hence substantial modifications of the hadron properties are expected to occur.
The spectral distribution of virtual photons measured in Au+Au collisions at 2.42 GeV center of mass energy indicates strong medium effects beyond pure superposition of individual NN collisions. We present multi-differential distributions of low-mass electron pairs measured in Au+Au collisions at 2.42 GeV center of mass energy. The data is analyzed in terms of excess radiation above a conventional cocktail of contributions from meson decay after thermal freeze-out. This strong excess radiation is remarkably well described assuming emission from a thermalized system. To gain deeper understanding of the microscopic origin of the excess radiation, we extracted it centrality dependent true (not blue-shifted) temperature, its azimuthal distribution and polarization, as well as mass dependent effective slope parameter. Virtual photon spectra will be confronted with results of other experiments as well as with available model calculations.

Centralised submission by Collaboration Presenter name already specified Theory HADES